Water test methods

COAGULATION FLOCCULATION JAR TEST
SUMMARY OF METHOD The coagulation – flocculation jar test is carried out to determine
chemicals and their dosages, and conditions required in order to reduce
suspended, colloidal, and non-settleable matter from water by chemical
coagulation – flocculation, followed by gravity settling.
APPARATUS 1. Multiple Stirrers – with continuous speed variation from about 20 to 150
rpm. The stirring paddles should be of light gauge, corrosion resistant
material, all of the same configuration and size. An illuminated base to
observe the floc formation.
2. Beakers – glass beakers, 1000 to 1500 ml capacity.
3. Reagent Racks – for introducing each test solution to all beakers
simultaneously. There should be at least one rack for each test solution
or suspension.
REAGENTS 1. Water – conforming to specifications Type III.
2. Prime Coagulants Concentration (10g/litre) :
a. Alum [ Al2 (SO4)3. 18H2O].
b. Ferric Sulphate [Fe2 (SO4)3. XH2O].
c. Ferric Chloride [FeCl3. 6H2O].
d. Ferrous Sulphate [FeSO4. 7H2O].
e. Magnesium Carbonate [MgCO3. 3H2O].
f. Sodium Aluminate [NaAlO2].
3. Coagulant Aids – activated silica, polyelectrolytes (anionic, cationic and
neutral).
4. Oxidising Agents – Chlorine (Cl2), Chlorine dioxide (ClO2), Potassium
permaganate (KMnO4), Calcium hypochlorite [CaO(ClO). 4H2O], Sodium
hypochlorite (NaClO).
5. Alkalis – Calcium carbonate (CaCO3), Dolomitic lime (58% CaO, 40%
MgO), Lime-hydrated [Ca(OH)2] Magnesium oxide (MgO), Sodium
carbonate (Na2CO3), Sodium hydroxide (NaOH).
6. Weighting Agents – Bentonite, Kaolin, Fuller’s earth, other clays and
minerals.
PROCEDURE 1. Place equal volumes (1000 ml) of sample into each beaker (1500 ml
capacity) and record the temperature of the sample.
2. Start the multiple stirrer at flash mix speed (approximately 120 rpm) for
all beakers. Add the test solutions or suspensions at predetermined
dosage levels and sequences. Flash mix for approximately 1 minute
after the addition of chemicals. Record the flash mix time and mixer
speed (rpm).
3. Reduce the speed to the minimum required, to keep floc particles
uniformly suspended throughout the ‘slow mix’ period. Slow mix for 20
minutes. Record the mixer speed (rpm).
4. After the slow mix period, withdraw the paddles and observe settling of
floc particles. Record the time required for the bulk of the particles to
settle.
5. After 15 minutes of settling, record the sample temperature and by
means of a pipet, withdraw supernatent liquor for conducting colour,
turbidity, pH, non-reactive and/or colloidal silica and other required
analysis.
INTERFERENCES 1. Temperature changes during test – Thermal or convection currents may
occur, interfering with the settling of coagulated particles.
2. Gas release during test – Floatation of coagulated floc may occur due to
gas bubble formation, caused by mechanical agitator, temperature
increase or chemical reaction.
3. Testing period – Biological activity or other factors may alter the
coagulation characteristics of water upon prolonged standing. Therefore,
the period between sampling and testing should be kept to a minimum.
1

NOTES 1. All polyelectrolytes are classified as anionic, cationic, or neutral,
depending upon their composition. A small dosage, under 1 ppm, may
permit a reduction in the dosage or complete elimination of the
coagulant.
2. It is recognized that reproducibility of results is important. To
demonstrate reproducibility, the so-called 3 and 3 procedure is
suggested. In this procedure, duplicate sets of 3 breakers each, are
treated simultaneously with the same chemical dosages in beakers 1 &
4, 2 & 5 and 3 & 6.
3. A suggested format for recording the results is given below:
FORMAT FOR RESULTS RECORDING
STATION - DATE -
LOCATION -
SAMPLE -
pH -
TURBIDITY -
COLOUR -
TEMPERATURE -
SAMPLE SIZE (ml) -
2

S. No.
Beaker No.
1 2 3 4 5 6
1. Chemicals, * mg/litre
a.
b.
c.
.
.
.
2. Flash mix speed, rpm
3. Flash mix time, minutes
4. Slow mix speed, rpm
5. Slow mix time, minutes
6. Temperature, o
C.
7. Time first floc, minutes
8. Floc size, mm (approx.)
9. Settling rate
10. Supernatent Tests:
a. Turbidity
b. pH
c. Colour
d. Non-reactive/collidal Silica
* Indicate order of addition of Chemicals.
3

COLOUR
SUMMARY OF METHOD Sample colour is visually compared with a standard Chloroplatinate
colour solution. The unit of colour (Hazen unit) is that produced by 1mg
platinum/litre in the form of the chloroplatinate ion.
APPARATUS 1. Nessler tubes – matched, 50 ml capacity, tall form.
2. pH meter.
REAGENTS 1. Water – conforming to specifications Type II.
2. Standard Stock Solution (colour of 500 units)
Dissolve 1.246 g Potassium chloroplatinate, K2PtCl6, (equivalent to 500
mg Pt) and 1.00g Cobaltous chloride, CoCl2.6H2O, (equivalent to about
250 mg Co) in water with 100 ml Hydrochloric acid (sp gr 1.19) and
dilute to 1 litre with water.
3. Colour Standards
Prepare standards having colours of 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,
60 and 70 units by diluting suitable volumes of standard stock solution
(3.2) to 50 ml with water in nessler tubes.
PROCEDURE 1. Place 50 ml of sample in a Nessler tube.
2. Compare the colour of the sample with standard colour by looking
vertically downwards against a white surface.
3. If the colour exceeds 70 units, dilute with water until the colour is within
the range of the standards.
4. If the sample is turbid, report as ‘apparent colour’.
5. Measure the pH of the sample.
CALCULATIONS 1. Calculate colour unit (Hazen Units) by the following equation:
Colour unit = A x 50
B
Where:
A = estimated colour of the diluted sample.
B = milliliters of sample.
2. Report colour results in whole numbers and record as follows:
Colour Unit Record to Nearest
1-50 1
51-100 5
101-250 10
251-500 20
Report Sample pH.
INTERFERENCES 1. Even a slight turbidity causes the apparent colour to be noticeably
higher than the true colour, therefore turbidity should be removed before
measurement of true colour.
2. The colour value of water is extremely pH dependent and invariably
increases as the pH of the water is raised. When reporting a colour
value, specify the pH at which colour is determined.
4

CONDUCTIVITY
SUMMARY OF METHOD The conductivity cell is dipped in the sample contained in a beaker and
the conductivity is read directly from the conductivity meter.
APPARATUS 1. Conductivity meter.
2. Conductivity cells with cell constants from 0.01 to 10 cm-1
.
3. Thermometer, accurate to 0.5o
C, when the instrument is not provided
with manual or automatic temperature compensation.
REAGENTS 1. Water – conforming to specifications Type I.
2. Potassium Chloride (KCl) – Dry at 105o
C for 2 hours.
Reference Solution A (Conductivity of 97838 microsiemens/cm at 18o
C
and 111342 microsiemens/cm at 25o
C) – Dissolve 74.2460 g of
potassium chloride in water and dilute to 1 litre at 20o
± 2o
C.
Reference Solution B (Conductivity of 11167 microsiemens/cm at 18o
C
and 12856 microsiemens/cm at 25o
C) – Dissolve 7.4365g of potassium
chloride in water and dilute to 1 litre at 20 ± 2o
C.
Reference Solution C (Conductivity of 1220.5 microsiemens/cm at 18o
C
and 1408.8 microsiemens/cm at 25o
chloride in water and dilute to 1 litre at 20 ± 2o
C.
Reference Solution D (Conductivity of 146.93 microsiemens/cm at 25o
C)
– Dilute 100 ml of reference solution C to 1 litre with water at 20 ± 2o
C
shortly before using.
PROCEDURE 1. Determination of Cell Constant
1.1 Rinse the conductivity cell with at least three portions of standard
potassium chloride solution.
1.2 Thermostat the reference standard at 18 or 25o
C and measure
conductivity in accordance with the instrument manufacturer
instruments.
K1 + K2
Cell constant (A) = ----------
Kx
Where:
K1 = Conductivity of the reference standard potassium chloride
solution (microsiemens/cm) at the temperature of measurement.
K2 = Conductivity of water (microsiemens/cm), used to prepare the
reference solution, at the temperature of measurement.
Kx = Measured conductance (microsiemens/cm).
2. Measurement of Conductivity
2.1 Conductivity Below 10 microsiemens/cm.
2.1.1 Use a flow type conductivity cell. Adjust the sample stream to a proper
flow rate and bring the temperature to a steady value as near 25o
C as
possible. Read the temperature to the nearest 0.5o
C.
2.1.2 If the conductivity meter is provided with a manual temperature
compensator, adjust this to the sample temperature value.
2.1.3 If an automatic temperature compensator is provided, no adjustment is
necessary but sufficient time must be allowed to permit equalization of
temperature.
2.1.4 Read the conductivity.
2.1.5 If the instrument has no means of temperature compensation, determine
a temperature correction to convert readings to 25o
C (see notes).
2.2 Conductivity Above 10 microsiemens/cm.
2.2.1 Either a flow-type, dip-type, or piped-type cell may be used. If a flow-
type cell is used, proceed in accordance with 4.2.1.
2.2.2 If another type of cell is used, rinse the cell thoroughly several times with
water and then two or more times with the sample. Measure the
conductivity and the temperature (to the nearest 0.5o
C) on successive
portions of the sample until a constant value is obtained.
5

2.2.3 Proceed in accordance with 4.2.1.2, 4.2.1.3 and 4.2.1.5.
CALCULATIONS 1. Calculate the conductivity of the sample as follows:
Conductivity (K), microsiemens/cm = A x Kx
Where:
A = cell constant.
Kx = measured conductance of the sample, in microsiemens/cm.
PRECISION 1. Results obtained should not differ by more than 1% of the conductivity.
INTERFERENCES 1. Exposure of a sample to the atmosphere may cause changes in
conductivity due to loss or gain of dissolved gases.
2. The carbondioxide, normally present in the air, can drastically change
the conductivity of pure water. Contact with air should be avoided by
using flow through or inline cells.
NOTES 1. The unit of conductivity is siemens per centimeter. The conductance is
directly proportional to the cross-sectional area, A (cm2
) and inversely
proportional to the length of the path, L (cm)
K x A
Conductance = ---------
L
The conductance measured between opposite faces of a centimeter
cube, K, is called specific conductivity.
2. Recommended cell constants for various conductivity ranges are given
below:
Range of conductivity, Cell constant,
Microsiemens/cm Cm-1
0.05 to 20 0.01
1 to 200 0.1
10 to 2000 1
100 to 20000 10
1000 to 2000000 50
3. The conductivity of water and aqueous solutions depends strongly upon
the temperature. To avoid making a correction, it is necessary to hold
the temperature of the sample to 25 ± 0.5o
C. If this cannot be done, the
temperature coefficient is determined by conductivity and temperature
measurements on the sample over the required temperature range. The
conductivity is plotted against temperature and from this curve a table of
temperature correction factors may be prepared, or the ratio of
conductivity at temperature, T, to conductivity at 25o
C may be plotted
against temperature and this ratio taken from the curve.
4. When using an instrument provided with a manual or automatic
temperature compensator, follow the manufacturers instructions to
calibrate the compensator or check its accuracy and applicability to the
sample being tested.
6

pH
SUMMARY OF METHOD The pH meter and associated electrodes are standardized against two
reference buffer solutions, which are close to the anticipated sample pH.
The sample measurement is made under specified conditions and
prescribed techniques.
Apparatus 1. Laboratory pH meter together with its associated glass and reference
electrodes.
Reagents 1. Water – conforming to specifications Type I.
2. Reference Buffer Solution
a. Borax (pH = 9.18 at 25o
C) – Dissolve 3.80 g of sodium
tetraborate decahydrate (Na2B4O7. 10H2O) in water and dilute to
1-litre.
b. Phosphate (pH = 6.86 at 25o
dihydrogen phosphate (dried at 130o
C for 2 hours) (KH2PO4)
and 3.53g of anhydrous disodium hydrogen phosphate (dried at
130o
C for 2 hours) (Na2HPO4) in water and dilute to 1-litre.
c. Phthalate (pH = 4.00 at 25o
hydrogen phthalate (dried at 110o
C for 2 hours) (KHC8H4O4) in
water and dilute to 1-litre.
d. Tetroxalate (pH = 1.68 at 25o
tetroxalate dihydrate (KHC2H4H2C2O4. 2H2O) in water and dilute
to 1-litre.
e. Sodium Bicarbonate – Sodium Carbonate (pH = 10.01 at 25o
C)
– Dissolve 2.092g of sodium bicarbonate (NaHCO3) and 2.640g
of sodium carbonate (dried at 275o
C for 2 hours) (Na2Co3) in
water and dilute to 1-litre.
PROCEDURE 1. Switch on the pH meter, allow it to warm up thoroughly, and bring it to
electrical balance with the manufacturer’s instructions.
2. Select two reference buffer solutions, the pH values of which are close
to the anticipated sample pH and if possible bracket the sample pH.
3. Standardize the pH meter with the above two (4.2) reference buffer
solutions in accordance with the manufacturer’s instructions.
4. Wash the electrodes with water and fill the beaker (provided with a
thermometer) with water sample. Insert the electrodes into the beaker
and record the pH of the water sample when the drift is less than 0.02
units in 1-minute.
CALCULATIONS 1. Most pH meters are calibrated in pH units and the pH of the sample is
obtained directly by reading the meter scale.
2. Report the temperature of measurement to the nearest 1o
C.
3. Report the pH of the test solution to the nearest 0.01pH units when the
pH measurement lies between 1.0 and 12.0.
4. Report the pH of the test solution to the nearest 0.1 pH units when the
pH measurement is less than 1.0 and greater than 12.0.
PRECISION 1. The precision of this method is 0.05 pH units for pH measurements
between 1.0 and 12.0.
2. When the pH is less than 1.0 and greater than 12.0, the precision is 0.1
pH units.
3. In order to attain this precision the condition of the instrumentation and
the technique for standardization and operation is extremely important.
7

INTERFERENCES 1. The true pH of an aqueous solution is affected by the temperature,
which can be compensated automatically in many instruments or can be
manually compensated in most other instruments. The temperature
compensation corrects for the effect of the water temperature on the
instrument, including the electrodes, but does not correct for
temperature effects on the chemical system being monitored. It does not
adjust the measured pH to a common temperature; therefore, the
temperature should be reported for each pH measurement.
2. The glass electrode reliably measures pH is nearly all aqueous solutions
and in general, is not subject to solution interference from colour,
turbidity, colloidal matter, oxidants or reductants.
3. The pH response of most glass electrodes is imperfect at both ends of
the pH scale. The indicated pH value of highly alkaline solutions will be
too low. This is minimized by the selection of proper glass electrode.
4. The indicated pH value of strong aqueous solutions of salts and strong
acids having a pH less than 1, will often be higher than the true pH
value. This is termed the negative error and the pH indicated is
somewhat greater than the true pH.
5. The pH response of the glass electrode may be impaired by a few
coating substances such as oily materials and particulates. The
electrodes can be restored to normal by an appropriate cleaning
procedure recommended by the manufacturer.
NOTES 1. The pH is the negative logarithm to the base ten of the conventional
hydrogen ion activity.
It is derived from the electromotive force (emf) of the cell,
reference electrode solution glass electrode
(E – Er) F
pH = pHr = --------------
2.3026 RT
Where:
pHr = pH of the reference buffer.
E = emf obtained when the electrodes are immersed in the sample.
Er = emf obtained when the electrodes are immersed in a reference
buffer solution.
F = Faraday constant = 96485.3415 sA/mol or 96500 C mol-1
R = Gas constant = 8.314 (J)(K-1
)(mol-1
)
T = absolute temperature.
2. New glass electrodes and those which have been stored dry, shall be
conditioned and maintained as recommended by the manufacturer. If is
necessary to keep the immersible ends of the electrodes in water
between measurements. For prolonged storage, glass electrodes may
be allowed to become dry, but the junction and filling openings of
reference electrodes should be caped to decrease evaporation. Glass
electrodes should be stored as recommended by the manufacturer and
reference electrodes in saturated potassium chloride solution.
3. Both the saturated Calomel electrode and silver-silver chlorine electrode
are satisfactory for measurement at room temperature. The silver-silver
chloride electrode is recommended for measurement at elevated
temperatures where its potential is more stable than that of the saturated
calomel electrode.
4. Where emulsions of free oil and water are to be measured for pH, it is
necessary to clean the glass electrodes thoroughly after each
measurement. The cleaning is done by washing with soap or detergent
and water, followed by several rinse with water, after which, the lower
third of the electrode is immersed in hydrochloric acid (1+9) and finally
washed thoroughly with water.
8

5. If the sample contains sticky soaps or suspended particles, the cleaning
is done with a suitable solvent or by chemical treatment, to dissolve the
deposited coating. After cleaning with solvent the lower third is
immersed in hydrochloric acid (1+9) followed by thorough washing with
water.
6. If glass electrode has failed to respond the treatment as described in
8.4, it is immersed in chromic acid cleaning solution for several minutes.
This drastic treatment, limits the life of electrode and is used only as an
alternative to discarding it. After chromic acid treatment, the electrode is
allowed to stand in water overnight.
7. If the electrode fails to respond to chromic acid cleaning, it is immersed
in a 20% solution of ammonium bifluoride (NH4HF2) for about 1-minute.
This treatment removes a portion of the bulb glass and should be used
only as a last resort. After the fluoride treatment the electrode is
thoroughly rinsed with water and conditioned, as is recommended for a
new glass electrode.
9

TURBIDITY(Nephelometric)
SUMMARY OF METHOD The intensity of light scattered by the sample under given conditions is
compared with the intensity of light scattered by a standard reference
suspension under the same conditions.
APPARATUS 1. Nephelometer – covering the range 0 to 1000 NTU.
2. Sample tubes.
REAGENTS 1. Turbidity free water – water conforming to specifications Type I.
2. Stock Turbidity Suspension
Solution A – Dissolve 1.000 g of Hydrazine Sulphate [(NH2)2 H2SO4] in
turbidity free water and dilute to 100 ml in a volumetric flask.
Solution B – Dissolve 10.00 g of Hexamethylene Tetramine [(CH2)6 N4] in
turbidity free water and dilute to 100 ml in a volumetric flask.
2.1 In a 100 ml volumetric flask, mix 5.0 ml solution A with 5.0 ml Solution B.
Allow to stand for 24 hours at room temperature. Make up to the mark
with turbidity free water and mix well. The turbidity of this suspension is
400 NTU.
3. Standard Turbidity Suspension.
3.1 Dilute 10.0 ml of stock turbidity suspension (3.2.3) to 100 ml with
turbidity free water. The turbidity of this suspension is 40 NTU. Prepare
weekly this suspension.
4. Dilute Turbidity Standard
4.1 Dilute portions of the standard turbidity suspension (3.3.1) with turbidity
free water, as required. Prepare weekly.
PROCEDURE 1. Calibrate the Nephelometer with standard turbidity suspension for each
range, in accordance with the manufacturer’s instructions.
2. Replace the standard by the sample in the same tube after thoroughly
washing the tube with turbidity – free water or in an optically identical
tube and record the reading.
CALCULATIONS 1. Report the result as nephelos turbidity units (NTU).
10

SUSPENDED AND TOTAL DISSOLVED SOLIDS
(25 mg/litre or Less of Total Solids)
SUMMARY OF METHOD Total solids are determined by evaporation, or the suspended and
dissolved solids are separated by filtration and individually determined.
The suspended solids are dried and weighed. The solution of dissolved
solids is evaporated to dryness using a dish provided with a constant
level control. The residue is dried and weighed.
APPARATUS 1. Sample Reservoir – A covered 20-litre container of corrosion resistant
metal, TFE fluorocarbon, polyethylene, or chemical resistant glass with
necessary tubular connections.
2. Automatic Evaporation Assembly - A dust shield, constant level device,
heater and evaporation dish.
3. Sampling Device – A cooling coil with overflow pipe and solenoid valve
suitable for sampling from a water source to a continuous sample
evaporator. (The cooling coil is necessary, only when, sample is above
room temperature).
4. Membrane Filter Assembly - A borosilicate glass or stainless steel funnel
with a flat, fritted base of the same material, and membrane filters (0.45
micron pore size) to fit.
5. Glass Petri Dish, 150 mm diameter.
6. Evaporating Dish – A straight walled or round bottom platinum dish of 80
to 100 mm diameter and approximately 200 ml capacity.
REAGENTS 1. Purified, Chloroform or Benzene.
PROCEDURE 1. Select a volume of sample sufficient to yield on evaporation a residue of
approximately 25 mg.
2. Suspended Solids (W2)
2.1 Place the membrane filter in a petri dish and dry in an oven at 103o
C for
15 minutes or in a vacuum desiccator for 30 minutes. Weigh the filter to
the nearest 0.1 mg.
2.2 Filter the sample through membrane filter (4.2.1) using the filtration
assembly and the vacuum pump or water aspirator. Wash the residue
with chloroform or benzene. Place the filter in the petri dish.
2.3 Place the petri dish in the oven at 103o
C for 30 minutes. Reweigh the
filter and record the weight of the residue on the filter. (W2)
3. Total Solids and Dissolved Solids.
3.1 Weigh a platinum dish that has been dried at 103o
C for 1 hour and
cooled in a desiccator. Using evaporation assembly start the
evaporation of the selected volume of the sample for total solids (4.1)
(W1) or the filtrate from the suspended solids determination (4.2) for
dissolved solids (W3).
3.2 When the evaporation is almost complete remove the dish from the
assembly and dry at 103o
C for 1 hour in an oven. Cool in a desiccator
and weigh. Record the weight of the residue.
CALCULATIONS Calculate the result of each specific determination as follows:
W1 x 1000
Total Solids, mg/litre = ------------
V
W2 x 1000
Suspended solids, mg/litre = ------------
V
W3 x 1000
Total dissolved solids, mg/litre = ------------
V
Where:
11

W1 = grams of total solids.
W2 = grams of suspended solids.
W3 = grams of dissolved solids.
V = litres of sample used.
NOTES 1. Some evaporation residues readily absorb moisture, therefore rapid
weighing should be done.
2. Samples containing 25 mg/litre or less of total solids on which only the
total solids content is to be determined shall be immediately acidified
with 0.2 ml of hydrochloric acid (sp gr 1.19) per litre of water. If
suspended solids is to be separately determined, the sample, regardless
of total solids content, shall be filtered, as soon as possible and then
acidified.
12

SUSPENDED AND TOTAL DISSOLVED SOLIDS
(More than 25 mg/litre of Total Solids)
SUMMARY OF METHOD Total solids are determined by evaporation of an appropriate portion of
the sample and weighing the residue obtained. The suspended and
dissolved solids can be separated by filtration and then determined
individually. The suspended solids are dried and weighed and dissolved
solids are determined by weighing the residue, obtained by evaporating
the filtered sample.
APPARATUS 1. Sample Reservoir – A chemical resistant container of 1 to 4-litre
capacity, having a valve controlled outlet.
2. Membrane Filter Assembly - A borosilicate glass or stainless steel funnel
with a flat, fritted base of the same material, and membrane filters (0.45
micron pore size) to fit.
3. Glass Petri Dish, 150 mm diameter.
4. Evaporating Dish – A straight wall or round bottomed platinum dish of 80
to 100 mm diameter and approximately 200 ml capacity. A porcelain
dish may be substituted for the platinum dish.
5. Heater – Hot plate or steam bath for maintaining the temperature of the
evaporating sample near the boiling point.
REAGENTS 1. Purified, Chloroform or Benzene.
PROCEDURE 1. Measure a quantity of sample sufficient to yield, on evaporation,
approximately 25 mg of residue.
2. Suspended Solids
2.1 Place the membrane filter in a petri dish and dry in an oven at 103o
C for
15 minutes or in a vacuum desiccator for 30 minutes. Weigh the filter to
the nearest 0.1 mg.
2.2 Filter the sample through membrane filter (4.2.1) using the filtration
assembly and the vacuum pump or water aspirator. Place the filter in the
petri dish.
2.3 Place the petri dish in the oven at 103o
C for 30 minutes. Reweigh the
filter and record the weight of the residue on the filter.
3. Total Solids and Dissolved Solids.
3.1 Transfer the sample for total solids determination (4.1) or the filtrate from
suspended solid determination (4.2) to a sample reservoir.
3.2 Fill an evaporating dish (previously dried at 103o
C for 1 hour and
weighed) to within 6.3 mm of the top, with sample.
3.3 Evaporate the sample on a hot plate or steam bath. Periodically, add
sample from the reservoir to the dish until the reservoir is empty.
3.4 Dry the dist at 103o
C for 1 hour. Cool in a desiccator and weigh. Record
the weight of the residue in the dish.
CALCULATIONS 1. Calculate the result of each specific determination as follows:
W1 x 1000
Total Solids, mg/litre = --------------
V
W2 x 1000
Suspended solids, mg/litre = --------------
V
W3 x 1000
Total dissolved solids, mg/litre = --------------
V
Where:
W1 = grams of total solids.
W2 = grams of suspended solids.
W3 = grams of dissolved solids.
13

V = litres of sample used.
NOTES 1. Some evaporation residues readily absorb moisture, therefore rapid
weighing should be done.
2. Suspended solids are defined as those solids, exclusive of gases and in
non-liquid state, which are dispersed in water to give a heterogeneous
mixture. Dissolved solids (exclusive of gases) are dispersed in water to
give a homogenous liquid and total solids is the sum of suspended and
dissolved solids.
14

ALKALINITY
(Titration Method, 10 to 500 mg/litre)
SUMMARY OF METHOD The sample is titrated with acid solution to a designated pH and the end
point is determined using internal indicator.
RANGE 10 to 500 mg/litre as CaCO3.
2. Phenolphthalein Indicator Solution (5.0 g/litre) – Dissolve 0.5g of
phenolphthalein in 50 ml of ethyl alcohol (95%) and dilute to 100 ml with
water.
3. Standard Hydrochloric Acid (0.02 N) – Dilute 1.66 ml of hydrochloric acid
(sp gr 1.19) to 1 litre with water. For standardization - see notes.
4. Mixed Bromocresol Green – Methyl Red Indicator Solution – Dissolve 20
mg of methyl red and 100 mg of bromocresol green (sodium salt) in
either 100 ml of water or 100ml of ethyl alcohol (95%).
5. Methyl Orange Indicator Solution (0.5 g/litre) – Dissolve 0.05g of methyl
orange in water and dilute to 100 ml.
6. Sodium Thiosulphate Solution (0.1 N) – Dissolve 2.5g of sodium
thiosulphate (Na2S2O3. 5H2O) in 50 ml of water, add 0.011g of sodium
carbonate. Dilute to 100 ml and allow to stand for 24 hours.
PROCEDURE 1. Phenolphthalein Alkalinity (P-Alkalinity)
1.1 Place 50 ml sample in a titration flask and add 2 drops of
phenolphthalein indicator.
1.2 Titrate over a white surface 0.02 N standard hydrochloric acid from a
pink colour to a colourless end point (A).
2. Total Alkalinity by Mixed Indicator
2.1 Add 3 drops of the mixed indicator to the solution in which the
phenolphthalein alkalinity has been determined.
2.2 Titrate over a white surface with 0.02 N standard hydrochloric acid to the
required end point.
Above pH 5.2 - Greenish blue
At pH 5.0 - Light blue
pH 4.8 - Pink grey with bluish tinge
pH 4.6 - Light Pink
3. Total Alkalinity (M-Alkalinity) by Methyl Orange
3.1 Add 2 drops of methyl orange indicator to the solution in which the
phenolphthalein alkalinity has been determined.
3.2 Titrate over a white surface with 0.02 N standard hydrochloric acid to the
required end point. (At pH 4.6 the colour changes to orange and at pH
4.0 to pink) (B).
CALCULATIONS
A x N x 50,000
1. Phenolphthalein Alkalinity, mg/litre as CaCO3 = ---------------------
V
B x N x 50,000
2. M-Alkalinity (Total Alkalinity), mg/litre as CaCO3 = ----------------------
V
Where:
A = millilitres of standard hydrochloric acid to reach the
phenolphthalein end point
B = total milliliters of standard hydrochloric acid to reach the mixed
indictor or methyl orange end point.
N = normality of hydrochloric acid.
V = milliliters of sample.
3. Alkalinity Relationship.
15

The following table gives the stoichiometric classification of the three
principal forms of alkalinity present in water.
Results of
Titration
Hydroxide
Alkalinity
(as CaCO3)
Carbonate
Alkalinity
(as CaCO3)
Bicarbonate
Alkalinity
(as CaCO3)
P = 0 0 0 M
P < ½ M 0 2 P M – 2P
P = ½ M 0 2 P 0
P > ½ M 2 P – M 2 ( M – P) 0
P = M M 0 0
Where:
P = Phenolphthalein Alkalinity.
M = M-Alkalinity (or total alkalinity).
PRECISION 1. The precision of this method is ± 1 mg/litre as CaCO3.
INTERFERENCES 1. Free residual chlorine markedly affects the indicator colour response in
some water samples through its bleaching action. It can be removed by
the addition of sodium thiosulphate.
2. Natural colour or the formation of a precipitate during titration may mask
the colour change.
3. Salts of weak organic and inorganic acids also affect the titration.
NOTES 1. Reagent grade chemicals should be used for preparing the reagents.
2. Phenolphthalein indicator is used for alkalinity determination contributed
by hydroxide and half the carbonate. Indicators responding in the pH
range 4-5 are used to measure the alkalinity contributed by hydroxide,
carbonate and bicarbonate. The stoichiometric relationship between
hydroxide, carbonate and bicarbonate are valid only in the absence of
significant concentration of weak acid radicals other than hydroxide,
carbonate or bicarbonate.
3. The following pH values are suggested as the equivalence points for the
corresponding alkalinity concentration as calcium carbonate:
pH of 5.1 for total Alkalinities of about 30 mg/litre, pH of 4.8 for 150
mg/litre, and pH of 4.5 for 500 mg/litre.
3.1 Indicators effective in these ranges which give the most reliable results
are mixed indicator for higher pH values and methyl orange for pH
values below 4.6.
4. To standardize 0.2 N hydrochloric acid, Weigh accurately 0.088 ± 0.001
g of sodium carbonate (previously dried in a platinum crucible at 250o
C
for 4 hours) and transfer to a 500 ml conical flask. Add 50 ml of water to
dissolve the carbonate and add 2 drops of 0.1% solution of methyl red in
alcohol. Titrate with hydrochloric acid to the first appearance of a red
colour, and boil the solution carefully until the colour is discharged. Cool
to room temperature and continue the titration. Repeat the process of
boiling and titration until a faint red colour is obtained that is not
discharged on further heating.
5. Sulphuric acid can also be used in place of hydrochloric acid for titration.
16

ALKALINITY DUE TO HYDROXIDE
SUMMARY OF METHOD The sample is treated with a solution of strontium chloride to precipitate
dissolved carbonates and phosphates and the hydroxide ion is titrated
with a standard hydrochloric acid solution using phenolphthalein
indicator.
REAGENTS 1. Water – conforming to specifications type III.
2. Hydrochloric acid (0.02 N) – Dilute 1.66 ml of hydrochloric acid (sp gr.
1.19) to 1 litre with water. For standardization – see notes.
3. Phenolphthalein Indicator Solution (5.0 g/litre) – Dissolve 0.5 g of
phenolphthalein in 50 ml of ethyl alcohol (95%) and dilute to 100 ml with
water.
4. Strontium Chloride Solution (4.5 g/litre) – Dissolve 4.5 g of strontium
chloride (SrCl2. 6H2O) in water and dilute to 1 litre.
PROCEDURE 1. Transfer 100 ml of the sample to a 500 ml conical flask.
2. Add quickly, while swirling the flash, 1 ml of strontium chloride solution
for each milligram of carbonate or phosphate ion in the sample aliquot,
plus a 4 ml excess.
3. Stopper the flask loosely, boil the contents for a few seconds, and then
cool to room temperature.
4. Add 4 drops of phenolphthalein indicator solution and quickly titrate with
standard hydrochloric acid to a colourless end-point.
CALCULATIONS 1. Calculate the concentration of hydroxide ion, in mg/litre, as follows:
N x V1 x 17000
Hydroxide ion, mg/litre as OH =- -------------------
V
Where:
N = normality of standard hydrochloric acid.
V1 = millimetres of standard hydrochloric acid.
V = millimetres of sample.
2. Calculate the concentration of hydroxide ion, in mg/litre as CaCO3, as
follows:
Hydroxide ion, mg/litre as CaCO3 = B x 2.94
Where:
B = hydroxide ion, mg/litre as OH.
PRECISION 1. The single operator precision of the method can be expressed as
follows:
S = 0.05 mg/litre.
Where:
S = single operator precision.
INTEREFENCES 1. Aluminium, carbonates, chromates, phosphates, silicates, and some
organic matter affect the sample titration.
2. The effects of carbonates and phosphates are eliminated by the addition
of strontium chloride in excess.
2. To standardize 0.02 N hydrochloric acid, weigh accurately 0.088 ± 0.001
g of sodium carbonate (previously dried in a platinum crucible at 250o
C
for 4 hours) and transfer to a 500 ml conical flask. Add 50 ml of water to
dissolve the carbonate the add 2 drops 0.1% solution of methyl red in
alcohol. Titrate with hydrochloric acid to the first appearance of a red
colour, and boil the solution carefully until the colour is discharged. Cool
to room temperature and continue the titration. Repeat the process of
boiling and titration until a faint red colour is obtained that is not
discharged on further heating.
17

AMMONIA
(Indophenol Method, 10 to 500 micrograms/litre)
SUMMARY OF The sample is reacted with hypochlorite and phenol in the presence
METHOD of a manganous salt to produce an intense blue compound, the
intensity of which is measured spectrophotometrically at a wavelength of
630 nm.
RANGE 10 to 500 micrograms/litre as N.
APPARATUS 1. Spectrophotometer for use at 630 nm.
2. Matched pair of 10 mm and 50 mm cells.
2. Phenate Reagent Solution – Dissolve 2.5g of sodium hydroxide and 10g
of phenol in 100 ml of water. Prepare every week.
3. Hypochlorous Acid Solution – Add 10 ml of a 5% commercial bleaching
powder solution to 4ml of water. Adjust the pH to 6.5 to 7.0 with
hydrochloric acid (check with a narrow range pH paper). Prepare every
week.
4. Manganous Sulphate Solution – Dissolve 0.050g of manganous
sulphate (MnSO4.H2O) in 100 ml of water.
5. Ammonia Nitrogen Standard Solution (1ml = 0.5 microgram N) –
Dissolve 0.3819g of anhydrous ammonium chloride (NH4Cl), previously
dried at 105o
C for 1 hour, in water and dilute to 1 litre. Dilute 5.0 ml of
this solution to 1 litre.
CALIBRATION 1. Transfer 0.0, 1.0, 5.0, 10.0, 15.0 and 20.0 ml of the standard ammonia
nitrogen solution (1ml = 0.5 microgram N) to 25ml of volumetric flasks.
2. Add 0.05 ml of manganous sulphate solution and mix.
3. Add 0.5 ml of hypochlorous acid solution and add immediately but slowly
0.6 ml of the phenate solution. Dilute to 25ml with water.
4. Measure the absorbance of each standard at 630nm against the zero
standard (blank).
5. Prepare a calibration curve by plotting absorbance versus micrograms of
ammonia nitrogen.
PROCEDURE 1. Place 10 ml (or other suitable volume containing not
more than 10 micrograms ammonia nitrogen) of the sample in a 25 ml
volumetric flask.
2. Proceed in accordance with section 5.0 (5.2 to 5.4).
CALCULATIONS 1. Calculate the ammonia concentration in microgram/litre of nitrogen in
the sample, as follows:
A x 1000
Ammonia, micrograms/litre as N = -------------
V
Where:
A = micrograms of ammonia nitrogen observed from the calibration
curve.
V = millilitres of sample.
2. Calculate the ammonia concentration, in micrograms/litre of ammonia in
the sample, as follows:
Ammonia, microgram/litre as NH3 = B x 1.22
Where:
B = ammonia nitrogen, micrograms/litre.
INTERFERENCES 1. More than 500 mg/litre of alkalinity, more than 100 mg/litre of acidity,
colour and turbidity interfere.
These interferences can be removed by distillation prior to analysis.
18

AMMONIA
(Nessler’s Method 0.1 to 2 mg/litre)
SUMMARY OF METHOD The same is reacted with Nessler’s reagent (K2HgI4) to produce a
reddish brown colloidal compound, the intensity of which is measured
spectrophotometrically at a wavelength of 425 nm.
RANGE 0.1 to 2 mg/litre as N.
2. Matched pair of 10mm cells.
2. Ammonia Nitrogen, Standard solution (1ml = 0.01 mgN) – Dissolve
4.718g of ammonium sulphate [(NH4)2 SO4] (previously dried at 100o
C for
1 hour) in water and dilute to 1 litre. Dilute 10 ml of this solution to 1 litre.
3. Nessler Reagent – Dissolve 100 g of anhydrous mercuric iodide (HgI2)
and 70g of anhydrous potassium iodide (KI) in a small volume of water;
add this mixture slowly, with stirring, to a cooled solution of 160g of
sodium hydroxide in 500 ml of water. Dilute the mixture to 1 litre. Store
the solution in dark for 5 days and filter twice through a fritted glass
crucible before using. This reagent has a shelf life of 1 year, if stored in
dark.
4. Reagents for Sample Turbidity/Cloudiness Removal.
4.1 Sodium Hydroxide Solution (250g/litre) – Dissolve 250g of sodium
hydroxide in water and dilute to 1 litre.
4.2 Zinc Sulphate Solution (100 g/litre) – Dissolve 100g of zinc sulphate
(ZnSO4.7H2O) in water and dilute to 1 litre.
4.3 Sodium Potassium Tartrate Solution (300 g/litre) – Dissolve 30g of
sodium potassium tartrate tetrahydrate in 100ml of water.
4.4 Disodium Dihydrogen Ethylenediamine tetraacetate solution (500 g/litre)
– Dissolve 50g of disodium dihydrogen ethylenediamine tetraacetate
– dihydrate in water containing 10g of sodium hydroxide. Gently heat
to complete dissolution. Cool and dilute to 100 ml.
INTERFERENCES 1. Glycerine, hydrazine, and some amines will react with Nessler’s reagent
to give the characteristic yellow colour in the time required for the test.
2. Residual chlorine must be removed prior to ammonia determination with
sodium arsenite (NaAsO2) solution (lg/litre). One millilitre of this solution
will remove 1mg/litre of residual chlorine from the 500 ml sample.
3. Turbidity in the sample can be removed as follows:
Add 1 ml of Zinc sulphate solution to 100 ml sample and mix. Add
sodium hydroxide solution to raise the pH to about 10.5 (check with a pH
paper). Allow to settle and filter through whatman No. 40 filter paper. To
prevent cloudiness add 2 drops of sodium potassium tartrate solution or
disodium dihydrogen ethylenediamine tetraacetate.
2. The Nessler reagent should give the characteristic colour with ammonia
within 10 minutes after addition, and should not produce a precipitate
with small amounts of ammonia (0.04 mg in 50 ml volume). The solution
may be used without 5 day storage if it is filtered through a 0.45 –
micron membrane filter shortly before use.
19

CARBON DIOXIDE
(Bicarbonate Titration Method)
SUMMARY OF METHOD Carbon dioxide concentration is determined from measured values of pH
and bicarbonate ion.
APPARATUS 1. pH meter.
REAGENTS 1. Water – conforming to specifications Type.I.
2. Hydrochloric Acid, Standard (0.04N) – Dilute 3.42 ml of hydrochloric acid
(sp gr 1.19) to 1 litre with water and standardize with sodium carbonate
(dried at 250o
C for 4 hours) using methyl red indicator.
3. Methyl Red Indicator Solution (5g/litre) – Dissolve 0.5 g of methyl red in
100 ml of 95% ethanol.
PROCEDURE 1. Determine the pH of the sample.
2. Place 50 ml or less of sample water containing no more than 80 mg of
bicarbonate ion into a 200 ml beaker.
3. If the pH of the sample is above 8.3, titrate with 0.04N hydrochloric acid
to this pH value using the pH meter for end-point detection.
4. Continue to titrate to pH 4.5
5. Record the millilitres of hydrochloric acid required to titrate to pH 8.3 as
V1 and millilitres required to titrate from pH 8.3 to pH 4.5 as V2.
CALCULATIONS 1. Calculate the bicarbonate ion concentration using the following equation:
2440 x (V2 – V1)
Bicarbonate (HCO3), mg/litre = ----------------------
V
Where:
V = volume of sample is millilitres.
V1 = millilitres of hydrochloric acid required for titration to pH 8.3.
V2 = millilitres of hydrochloric acid required for titrating from pH 8.3 to
4.5
2. Calculate the free carbon dioxide concentration in mg/litre by using the
following equation for waters with pH values from 6 to 9:
Free CO2, mg/litre as CO2 = 1.60 x 10(6.0-pH)
x mg HCO3/litre.
3. Calculate free CO2 concentration in mg/litre as CaCO3 as follows:
Free CO2, mg/litre as CaCO3 = A x 1.14
Where:
A = concentration of CO2, mg/litre as CO2.
PRECISION 1. Precision of the bicarbonate determination is approximately 1mg/litre for
bicarbonate ion concentrations below 100mg/litre and 2 mg/litre in the
100 to 200 mg/litre bicarbonate ion range. Precision of carbon dioxide
measurement will be proportional to the fractional relationship between
bicarbonate ion and carbon dioxide values determined.
20

CARBON DIOXIDE
(Direct Titration of Free Carbon Dioxide)
SUMMARY OF METHOD Free carbon dioxide is reacted with sodium hydroxide to form sodium
bicarbonate. The end point of the reaction is detected electrometrically
or by means of a pH colour indicator.
2. Phenolphthalein Indicator Solution (5g/litre) – Dissolve 0.5g of
phenolphthalein in 100 ml of a 50% solution of ethyl alcohol in water.
3. Sodium Hydroxide solution, Standard (0.04N) – Dissolve 1.6 g of sodium
hydroxide in approximately 100 ml of water, add 0.1 g of barium
hydroxide and dilute to 1 litre with water. Allow the carbonate to settle
and standardize against the 0.04N hydrochloric acid.
4. Sodium Bicarbonate Solution (1g/litre) – Dissolve 0.1g of anhydrous
sodium bicarbonate in 50 ml of water and dilute to 1 litre. Prepare just
before use.
5. Hydrochloric Acid, standard (0.04 N) – Dilute 3.42 ml of hydrochloric
acid (sp. gr. 1.19) to 1 litre with water and standardize with sodium
carbonate (dried at 250o
C for 4 hours) using methyl red indicator.
6. Methyl Red Indicator solution (5g/litre) – Dissolve 0.5g of methyl red in
100 ml of 95% ethanol.
PROCEDURE 1. Place 100 ml of sample in a 250 ml breaker and add 5 drops of
phenolphthalein indicator solution.
2. If the sample remains colourless, titrate rapidly with standard sodium
hydroxide solution until the first faint pink colour is detectable in the
solution.
2.1 Alternatively, titrate the sample to pH 8.3 using a pH meter to detect the
end point.
CALCULATIONS 1. Calculate the free carbon dioxide content of the water in mg/litre using
the following equation:
Free CO2, mg/litre as CO2 = V x N x 440
Where:
V = millilitres of sodium hydroxide required to titrate 100 ml of
sample
N = normality of sodium hydroxide solution.
2. Calculate free CO2 concentration in mg/litre as CaCO3 as follows:
Free CO2, mg/litre as CaCO3 = A x 1.14
Where:
A = concentration of CO2, mg/litre as CO2.
PRECISION 1. Under the most favourable conditions, precision is approximately 10% of
the indicated carbon dioxide content.
INTERFERENCES 1. Cations or anions which affect the carbonate equilibrium or precipitate or
consume the reactant preferentially affect the accuracy. Aluminium, iron,
chromium and copper are examples of metal ions that may yield
erroneous results.
2. Abnormal results also may be obtained in the presence of ammonia,
amines, phosphate, borate, sulphide and nitrate.
3. Excessive dissolved solids also, will introduce error.
21

CHLORIDE
(Mercuric Thiocyanate Method, 0.05 to 1.4 mg/litre)
SUMMARY OF METHOD The sample is treated with ferric ammonium sulphate and mercuric
thiocyanate solutions. The chloride ion reacts with mercuric thiocyanate
to release the thiocyanate ion which combines with ferric ion to form red
ferric thiocyanate. The intensity of the colour is measured at a
wavelength of 463 nm.
RANGE 0.05 to 1.4 mg/litre as Cl.
2. Matched pair of 50 mm cells.
2. Ferric Alum Solution – Dissolve 5.0 g of ferrous ammonium sulphate [Fe
(NH4)2 (SO4)2. 6H2O] in 20 ml of water. Add 38 ml of nitric acid (sp gr
1.42) and boil to oxidize the iron and remove the oxides of nitrogen.
Dilute to 100 ml with water.
3. Mercuric Thiocyanate Solution – Dissolve 0.30 g of mercuric thiocyanate
[Hg(CNS)2] in 100 ml of absolute methanol in an amber bottle. Allow to
stand for 24 hours before using. This solution has a shelf life of 4 weeks.
4. Standard Sodium Chloride Solution (1 ml = 0.01 mg chloride) – Dissolve
1.649 g of sodium chloride (dried at 600o
C for 1 hour) in water and dilute
to 1 litre (solution A). Dilute 10.0 ml of solution A to 1 litre with water.
CALIBRATION 1. Prepare a series of standards by diluting 0, 0.5, 2.5, 5.0, 7.5, 10 and 14
ml of the standard sodium chloride solution (1 ml = 0.01 mg chloride) to
100 ml with water in volumetric flasks.
2. Proceed in accordance with section 6.0.
3. Prepare a calibration curve by plotting absorbance versus the
concentration of chloride in mg/litre.
PROCEDURE 1. Place 25 ml of sample in a 50 ml glass stoppered cylinder.
2. Add 5.0 ml of ferric alum solution and 2.5 ml of mercuric thiocyanate
solution. Mix thoroughly and allow to stand for 10 minutes.
3. Measure the intensity of colour at 463 m, against the reagent blank,
prepared by using 25 ml of water and following step 6.2, using 50 mm
matched absorption cells.
CALCULATIONS 1. Read the concentration of chloride ion in mg/litre directly from the
calibration curve prepared in accordance with section 5.0.
2. Calculate the chloride concentration in mg/litre as CaCO3 as follows:
Chloride, mg/litre as CaCO3 – A x 1.41
Where:
A = chloride concentration, mg/litre as Cl.
PRECISION 1. The precision of this method may be expressed as follows:
Sr = 0.054 X
So = 0.013 X
Where:
Sr = overall precision, mg/litre.
So = single operator precision, mg/litre.
X = concentration of chloride ion determined, mg/litre.
INTERFERENCES 1. Bromides, iodides, cyanides, thiosulphate, hydrazine and nitrites
interfere.
2. Morpholine concentrations greater than 6mg/litre may interfere.
3. Colour may also interfere depending upon its spectral absorbance.
4. Boric acid upto 13000 mg/litre does not interfere.
22

NOTES 1. Reagent grade chemicals should be used for preparing all the reagents.
2. Mercuric salts are very poisonous. Due precautions should be observed
when using these salts.
3. In the preparation of mercuric thiocyanate solution, a slight precipitate
may form and settle out after 24 hours. Only the clear, supernatent liquid
must be used.
4. Soak all new glassware in hot nitric acid (1+19) for several hours and in
water (halide free) between tests. Discard all glassware that appear
etched or scratched.
5. For best results, the temperatures of the standard solutions should be
within 1.0o
C of the reagent blank, and the samples.
23

CHLORIDE
(Mercuric Thiocyanate Method, Modified, 2 to 100 micrograms/litre)
SUMMARY OF METHOD A solution of lead nitrate is added to the sample followed by addition of
phosphate buffer. The resulting precipitation of lead phosphate
coprecipitates the Chloride in the sample. The sample is centrifuged and
the supernatent liquid discarded. The precipitate is dissolved in a ferric
iron-mercuric thiocyanate reaction medium and the Chloride is
determined Spectrophotometrically at 463 nm.
RANGE 2 to 100 micrograms/litre as Cl.
2. Matched pair of 50 mm Cells.
2. Ferric Nitrate Solution – Dissolve 8.0g of ferric nitrate [Fe(NO3)3. 9H2O]
in about 400 ml of water and add 58.5 ml of nitric acid (sp gr 1.42).
Dilute to 1 litre with water.
3. Lead Nitrate Solution – Dissolve 20g of lead nitrate [Pb(NO3)2] in water
and dilute to 1 litre.
4. Mercuric Thiocyanate Solution – Dissolve 0.30 g of mercuric thiocyanate
[Hg(SCN)2] in 100 ml of methanol. Store in amber bottle. Allow to stand
for 24 hours before using.
5. Standard Sodium Chloride Solution (1ml = 1 microgram of Chloride) –
Dissolve 1.649g of sodium chloride (dried at 600o
C for 1 hour) in water
and dilute to 1-litre (Solution A). Dilute 100 ml of Solution A to 1 litre
(Solution B). Finally dilute 10.0 ml of Solution B to 1 litre. This solution
should be prepared fresh before use.
6. Sodium Phosphate Solution – Dissolve 16.7 g of sodium dihydrogen
phosphate (NaH2PO4.7H2O) and 16.2 g of disodium hydrogen phosphate
(Na2HPO4.7H2O) in water and dilute to 1 litre.
CALIBRATION 1. Prepare a series of standards by diluting 0, 1.0, 5.0, 10.0, 15.0, and 25.0
ml of Standard Sodium Chloride Solution (1ml = 1 microgram of
chloride) to 250 ml in 250 ml glass stoppered bottles.
2. Proceed in accordance with Section 6.0 (6.2 to 6.7).
3. Prepare a calibration curve by plotting absorbance versus concentration
of Chloride in mg/litre.
PROCEDURE 1. Place 250 ml sample in a clean 250 ml glass stoppered bottle.
2. Add 5.0 ml of the lead nitrate solution to the bottle. Cap the bottle and
mix. Allow to stand for 2 minutes.
3. Add 5.0 ml of sodium phosphate solution and mix. Allow to stand for 5
minutes.
4. Centrifuge the capped bottle solution at 1500 rpm for 6 minutes. Decant
the supernatent liquid immediately after centrifuging.
5. Add 15.0 ml of ferric nitrate solution and mix to dissolve the precipitate.
6. Add 1.0 ml of mercuric thiocyanate solution and mix. Dilute to 25 ml with
water. Allow to stand for 10 minutes.
7. Measure the absorbance, against reagent blank prepared by taking 250
ml instead of sample and repeating the steps 6.2 to 6.6, at 463 nm using
50 mm matched cells.
CALCULATIONS 1. Read the concentration of chloride in micrograms/litre directly from the
calibration curve prepared in accordance with Section 5.0.
2. Calculate the chloride concentration in microgram/litre as CaCO3 as
follows:
Chloride, micrograms/litre as CaCO3 = A x 1.41
Where:
24

A = chloride concentration, micrograms/litre as Cl.
INTERFERENCES 1. See mercuric thiocyanate method (Section 9.0) for the determination of
Chloride.
NOTES 1. See mercuric thiocyanate method (Section 10.0) for the determination of
Chloride.
2. Lead nitrate is very toxic. Due precautions should be observed when
using this chemical.
3. 2 microgram/litre chloride represents 0.006 absorbance with respect to a
reagent blank when using 50 mm matched cells.
25

CHLORIDE
(Silver Nitrate Method, 5 mg/litre or more)
SUMMARY OF METHOD The sample is adjusted to a pH of 8.3 and titrated with silver nitrate
solution using potassium chromate indicator to a brick red colour.
RANGE 5 mg/litre or more as Cl.
2. Standard Silver Nitrate Solution (0.025N) – Dissolve 4.247g of silver
nitrate (dried to constant weight at 40o
C) in water and dilute to 1 litre.
Standardize against standard sodium chloride solution.
3. Standard Sodium Chloride Solution (0.025N) – Dissolve 1.461g of
sodium chloride (dried at 600o
C for 1 hour) in water and dilute to 1 litre.
4. Hydrogen Peroxide (30%).
5. Phenolphthalein Indicator Solution (10g/litre) – Dissolve 1g of
phenolphthalein in 100 ml of ethanol (95%), methanol or isopropyl
alcohol.
6. Potassium Chromate Indicator Solution (5%) – Dissolve 50g of
potassium chromate (K2CrO4) in 100 ml of water, and add silver nitrate
until a slight red precipitate is produced. Allow to stand for 24 hours in
dark. Filter and dilute to 1 litre.
7. Sodium Hydroxide Solution (10g/litre) – Dissolve 10g of sodium
8. Sulphuric Acid Solution (1+19) – Mix 1 volume of Sulphuric acid (sp gr
1.84) with 19 volumes of water.
PROCEDURE 1. Place 50 ml of sample into a 125 ml conical flask.
2. If Sulphite is present, add 0.5 ml of hydrogen peroxide solution and mix
for 1 minute.
3. Adjust the pH to the phenolphthalein endpoint (pH 8.3), using Sulphuric
acid solution, or sodium hydroxide solution.
4. Add 1 ml of potassium chromate indicator and mix.
5. Titrate with standard silver nitrate solution to a brick red colour.
6. Repeat 4.1 to 4.5 using 25 ml of sample diluted to 50 ml with water.
CALCULATIONS 1. Calculate the chloride ion concentration in the sample, in milligrams per
litre, as follows:
(V1 – V2) x N x 71000
Chloride, mg/litre as Cl = ------------------------------
V
Where:
V1 = millilitres of standard silver nitrate solution for the sample (4.1).
V2 = millilitres of standard silver nitrate solution for the sample (4.6).
N = normality of standard silver nitrate solution.
V = millilitres of sample (4.1).
2. Calculate the chloride concentration in mg/litre as CaCO3 as follows:
Chloride, mg/litre as CaCO3 = A x 1.41
Where:
A = Chloride concentration, mg/litre as Cl.
PRECISION The precision of this method may be expressed as follows:
ST = 0.013X + 0.70
So = 0.007X + 0.53
Where:
ST = overall precision, mg/litre
So = Single operator precision, mg/litre.
X = Concentration of Chloride ion determined, mg/litre.
INTERFERENCES 1. Bromide, iodide, and sulphide are titrated along-with the chloride.
2. Orthophosphate and polyphosphate interfere, if present, in
concentrations greater than 250 and 25 mg/litre, respectively.
26

3. Sulphite and objectionable colour or turbidity must be eliminated.
4. Compounds which precipitate at pH 8.3 may interfere.
NOTES 1. Reagent grade chemicals should be used for preparing all the reagents.
2. If the titration required more than 25ml of silver nitrate in 4.5, use a
smaller sample size.
27

CHLORINE DEMAND
SUMMARY OF METHOD A chlorinating solution of known concentration is applied in increasing
increments of chlorine concentration to a series of portions of the
individual sample of water to be tested. The residual chlorine is
determined at succeeding intervals of time.
REAGENTS 1. Water – conforming to specifications Type III.
2. Calcium Hydroxide Solution (10.7g/litre) – Weigh 10.7g of 100%
hydrated lime [Ca(OH)2] and suspend in water. Dilute to 1 litre.
3. Calcium Hypochlorite Solution (1ml = 0.5 to 100mg available Chlorine) –
Dissolve 145g of calcium hypochlorite (70% available chlorine, by
weight) in water and make up to 1 litre. Allow to settle and decant the
supernatent solution containing approximately 100 mg available chlorine
per ml. Dilute with water to give 0.5 to 100 mg of available chlorine per
ml. Standardize prior to use in accordance with 3.4.
4. Chlorine Water (1ml = 0.5 to 3mg available chlorine) – Pass gaseous
chlorine through water until the solution contains 0.5 to 3.0 mg available
chlorine per ml. For standardization add 10 ml of chlorine water to a
flask containing 10 ml of acetic acid (1+1) and 10 ml of potassium iodide
solution (5%). Titrate with 0.10N sodium thiosulphate solution using
starch indicator.
V1 x 3.546
Available Chlorine, mg/litre = ---------------
V
(V1 is millilitres of 0.10 N sodium thiosulphate solution used in the
titration and V is millilitres chlorine water taken for titration.)
5. Hydrochloric Acid (1+1) – Mix equal volumes hydrochloric acid (sp gr
1.19) and water.
PROCEDURE 1. Establishing Test Conditions
1.1 Ascertain the range of pH, time of chlorine contact, and the chlorine
application concentration to achieve the objective of Chlorination from
past experience, from literature survey, by experimentation, or from plant
conditions.
1.2 Determine the pH of each test and additions of chlorinating solutions
such that there is not less than five equal increments of the chlorine
application concentrations.
1.3 In each of a series of clean 1 litre glass containers, place a 500 ml
portions of the sample.
2. Trial Chlorination
2.1 To the first of the series of 500 ml portions of the samples, add the
maximum anticipated amount of chlorinating solution. Determine the pH
of the solution.
2.2 Adjust the pH (see notes).
2.3 Allow the chlorinated sample to stand for a minimum predetermined
time. Determine total and free available residual chlorine. Withdraw
successive samples at selected time intervals to cover the estimated
range of minimum to maximum contact times.
3. Chlorination
3.1 On the basis of information obtained by the trial chlorination, add desired
increments of chlorinating solution to separate 500 ml portions of the
sample. Determine the pH of each portion.
3.2 Adjust the pH (see notes)
3.3 Allow each portion of chlorinated sample to stand for a predetermined
time. Withdraw a portion of the sample and determine the total residual
chlorine.
28

CALCULATIONS Calculate the chlorine dosage, in mg/litre, for each increment of
chlorinating solution as follows:
Chlorine dosage, mg/litre = 2AB
Where:
A = millilitres of chlorinating solution added to 500 ml of sample.
B = milligrams of available chlorine per millilitre of the chlorinating
solution.
Determine the chlorine consumed, mg/litre, for each increment of
chlorine application as follows:
On log-log graph paper, plot, for a given chlorine application,
temperature, and pH, the chlorine consumed versus the contact time in
hours. Determine the value of the chlorine consumed at the intercept of
the line with the co-ordinate corresponding to a contact time of 1 hour.
Designate the value of this intercept as K. Determine the slop of the line
and designate as n. The straight lines for each chlorine application at
each temperature and pH are of the general form:
DT = K T t n
Where:
DT = Chlorine consumed at a given temperature .
t = contact time in hours.
KT = Chlorine consumed after 1 hour, mg/litre at a given temperature.
n = Slope of curve.
The chlorine consumed can be interpolated between test values by use
of the above expression.
NOTES 1. Chlorine requirement is the amount of chlorine required to achieve under
specified conditions the objectives of chlorination. Chlorine consumed is
the amount of chlorine expressed in mg/litre, determined as the
difference between the calculated concentration of chlorine applied at
zero time and the residual concentration measured at any selected
interval of time thereafter.
2. When the anticipated chlorine requirement is less than 600 mg/litre, use
the chlorinating solution which is to be used in ultimate plant treatment.
When the anticipated chlorine requirement is 600 mg/litre or more, use
the appropriate hypochlorite solution.
3. pH Adjustment
3.1 If the pH of the chlorinated sample is higher than the desired range, add
hydrochloric acid (1+1) to the chlorinated sample until the pH of sample
reaches the upper limit of the desired range.
3.2 If the pH of the chlorinated sample is lower than the desired range,
discard the sample and proceed with another series of sample portions,
as follows: add sufficient calcium hydroxide solution to bring the pH of
the unchlorinated sample portion to the midpoint of the desired pH
range.
3.3 If the chlorinating solution is chlorine water, add an additional 0.1 ml of
calcium hydroxide solution for each milligram of available chlorine to be
applied to the sample.
29

CHLORINE, RESIDUAL
(DPD Method, 0.02 to 4.0 mg/litre)
SUMMARY OF METHOD In the absence of iodide ion, free chlorine reacts with para-amino
diethylaniline (NN-Diethyl-p-Phenylene Diamine abbreviated as DPD) to
produce a red colour. Stepwise colour change is carried out to identify
monochloramine, dichloramine, and nitrogen trichloride. The individual
fractions are determined by titration with ferrous ammonium sulphate.
RANGE Upto 4mg/litre with minimum detection limit of 18 micrograms/litre.
REAGENTS 1. Water – conforming to specifications Type III, further treated to be free of
chlorine demand (see notes).
2. DPD Reagent – Dissolve 0.115g DPD sulphate, [NH2C6H4 N(C2H5)2].
H2SO4. 5H2O], in 50 ml of water containing 8 ml of sulphuric acid (1+3)
and 0.2g of EDTA disodium salt. Dilute to 100 ml and store in a brown
coloured glass bottle. Prepare fresh after every two weeks or discard it
when discoloured.
3. Phosphate Buffer Solution – Dissolve 2.4 g disodium-hydrogen
phosphate (Na2HPO4) and 4.6g of potassium-dihydrogen phosphate
(KH2PO4) in 50 ml of water. Add 10 ml of EDTA disodium salt (8g/litre)
and make up to 100 ml. Add 1 drop of mercuric chloride (20 mg/litre).
4. Sodium Arsenite Solution – Dissolve 0.5g sodium, arsenite (NaAsO2) in
100 ml of water.
5. Potassium Iodide, crystalline.
6. Potassium Iodide solution (5g/litre) – Dissolve 0.5g of potassium iodide
in water and dilute to 100 ml. Store in a brown coloured glass bottle.
Discard when yellow colour developes.
7. Ferrous Ammonium Sulphate Solution (1ml = 1mg chlorine) – Dissolve
1.106 g of ferrous ammonium sulphate [FeSO4(NH4)2SO4. 6H2O] in water
containing 1 ml of Sulphuric acid (1+3) and make up to 1 litre.
Standardize against potassium dichromate (for standardization see
notes).
8. Potassium Dichromate Standard Solution (0.003N) – Dissolve 0.147 g of
potassium dichromate (K2Cr2O7), previously dried at 103o
C for 2 hours,
in water and dilute to 1 litre.
9. Phenanthroline – Ferrous Sulphate Indicator Solution – Dissolve 1.48 g
of 1, 10 – phenanthroline monohydrate, and 0.70 g of ferrous sulphate
(FeSO4. 7H2O) in 100 ml of water.
PROCEDURE 1. Free Chlorine
1.1 Place 5.0 ml of DPD solution and 5.0 ml of phosphate buffer in a 250 ml
titration flask.
1.2 Add 100 ml of sample and mix.
1.3 Titrate with ferrous ammonium sulphate solution until the red colour is
discharged.
1.4 Record the volume of ferrous ammonium sulphate in ml used in the
titration as A.
2. Monochloramine (NH2Cl)
2.1 To the solution after titration for free chlorine (4.1) add 2 drops of
potassium iodide solution (5g/litre) and continue the titration.
2.2 Record the total volume of ferrous ammonium sulphate in ml as B. For
free chlorine + monochloramine)
3. Dichloramine (NHCl2)
3.1 To the solution after titration for monochloramine (4.2) add about 1 g of
potassium iodide and mix rapidly to dissolve, and allow to stand for 2
minutes.
3.2 Continue titration with ferrous ammonium sulphate.
3.3 Record the total volume of ferrous ammonium sulphate in ml as C (for
free chlorine + monochloramine + dichloramine).
4. Nitrogen Trichloride (NCl3)
30

4.1 Place a small crystal of potassium iodide in a 250 ml titration flask, add
100 ml of sample and mix.
4.2 Transfer the contents (4.4.1) to another flask containing 5 ml each of
buffer solution and DPD solution.
4.3 Titrate rapidly with ferrous ammonium sulphate solution.
4.4 Record the volume of ferrous ammonium sulphate in ml as D.
5. Total Available Chlorine
5.1 Place 1 g of potassium iodide in a 250 ml titration flask, add 100ml of
sample and mix.
5.2 Transfer the contents (4.5.1) to another flask containing 5 ml each of
buffer solution and DPD solution and allow to stand for 2 minutes.
5.3 Titrate with ferrous ammonium sulphate solution and record the volume
in ml as V1.
CALCULATIONS
V1 x 100
1. Total available chlorine, mg/litre as Cl = -------------
V
Where:
V1 = millilitres of ferrous ammonium sulphate used for total available
chlorine.
2. The following table may be used to determine various constituents:
TITRATE VALUE NCl3 – ABSENT NCl3 – PRESENT
A Free Chlorine Free Chlorine
B – A NH2Cl NH2Cl
C – B NHCl2 NHCl2 + ½ NCl3
D - Free chlorine + ½ NCl3
2 (D – A) - NCl3
C – D - NHCl2
INTERFERENCES 1. Copper and dissolved oxygen interfere in measurement, however, this is
suppressed by using ETDA in phosphate buffer.
2. Nitrite nitrogen up to 5 mg/litre does not interfere.
3. For accurate results, careful pH control is essential. At the proper pH of
6.2 of 6.5, the red colour produced may be titrated to sharp colourless
endpoints.
3.1 The titration should be carried out as soon as the red colour is formed in
each step.
3.2 Too low a pH in the first step will tend to make the monochloramine
show in the free-chlorine step and the dichloramine in the
monochloramine step.
3.3 Too high a pH may cause dissolved oxygen to give colour.
4. Oxidising manganese gives a colour leading erroneous measurement.
To correct for this, 5.0 ml buffer solution, one small crystal of potassium
iodide and 0.5 ml sodium arsenite solution in titration flask. Add 100 ml
of sample and mix. 5.0 ml of DPD solution, mix and titrate with standard
ferrous ammonium sulphate until red colour discharged. Subtract the
reading ‘A’ as given the procedure or from 4.5 as the case may be.
2. For preparing chlorine demand free water, approximately 20 mg/litre of
available chlorine to III reagent grade water. Allow the chlorinated to
stand about 1 week in the absence of sunlight no residual chlorine
remains.
3. For standardizing ferrous ammonium sulphate (1 litre), place 25 ml of
0.003 N potassium dichromate 500 ml titration flask and dilute to about
250 ml and 20 ml of sulphuric acid (sp gr 1.84) and allow solution to
31

cool. Titrate with ferrous ammonia sulphate, using phenanthroline-
ferrous sulphate indicator.
Calculate the strength of ferrous ammonium sulphate solution as
follows:
Strength of ferrous ammonium sulphate solution g/litre
V1 x N1 x 392
= -------------------
V
Where:
V1 = millilitres of potassium dichromate solution
N1 = normality of potassium dichromate solution
V = millilitres of ferrous ammonium sulphate soluion.
32

COPPER
(Neocuproine Method, 2 to 1000 micrograms/litre Cu)
SUMMARY OF METHOD The copper is reduced with hydroxylamine-hydrochloride. The pH of the
aqueous phase is adjusted to 4.0-6.0 with sodium acetate buffer. The
cuprous ion is then reacted with neocuproine (2,9 – dimethyl –1, 10 –
phenanthroline) and the yellow complex extracted either with chloroform
or isoamyl alcohol. The intensity of colour, when extracted with
chloroform, is measured at 457 nm and at 454 nm when extracted with
isoamyl alcohol.
RANGE 20 to 1,000 micrograms/litre Cu (10 mm cell).
2 to 150 micrograms/litre Cu (50 mm cell).
2 to 100 micrograms/litre Cu (100 mm cell).
APPARATUS 1. Spectrophotometer for use at 454 and 457 nm.
2. Matched pairs of 10 mm, 50 mm & 100 mm cells.
REAGENTS 1. Water – conforming to specifications Type-I.
2. Copper Stock Solution (200 mg/litre) – Place 0.200 g electrolytic grade
copper in a 250 ml beaker, add 3 ml of water and 3 ml of nitric acid (sp
gr 1.42). After the metal has completely dissolved, add 1 ml sulphuric
acid (sp gr 1.84) and evaporate on a hot plate to nearly dryness.
Dissolve the residue in water and dilute to 1 litre.
3. Copper Standard Solution (2mg/litre) – Dilute 100 ml of copper stock
solution (4.2) to 1 – litre. Again dilute 100 ml of this diluted solution to 1
litre.
4. Hydrochloric Acid (sp gr 1.19).
5. Hydroxylamine Hydrochloride Solution (20%) – Dissolve 40g of
hydroxylamine hydrochloride (NH2OH.HCl) in water and dilute to 200 ml.
Remove traces of copper from this solution by treating with neocuproine
solution and extracting with chloroform or isoamyl alcohol.
6. Neocuproine Solution (1g/litre) – Dissolve 0.1 g of neocuproine in 50 ml
of isopropyl alcohol. Dilute to 100 ml with water.
7. Sodium Acetate Solution (275 g/litre) – Dissolve 55g of sodium acetate
trihydrate (NaC2H3O2.3H2O) in water and dilute to 200 ml. Remove
traces of copper from this solution by treating with hydroxylamine
hydrochloride, neocuproine and extracting with chloroform or isoamyl
alcohol.
8. Chloroform Solvent – Mix 9 volumes of chloroform (CHCl3) with one
volume of isopropyl alcohol.
9. Isoamyl Alcohol, copper free.
10. Isopropyl Alcohol, copper free.
CALIBRATION 1. Prepare a series of standards (at least five concentrations) to cover the
expected range of copper concentrations by diluting appropriate
volumes of copper standard solution (4.3, 1 ml = 2 micrograms Cu) as
follows:
1.1 Place the required volumes of copper standard solution (4.3) in 250 ml
separatory funnels.
1.2 Add 0.4 ml hydrochloric acid (sp gr 1.19) to each funnel and add water
to make 200 ml.
1.3 Prepare a blank (zero standard) by diluting 0.4 ml hydrochloric acid (sp
gr 1.19) to 200 ml with water.
1.4 Proceed in accordance with section 6.0 (6.2 to 6.7) and measure the
absorbance of each individual standard.
1.5 Use the organic liquid from the bland as a reference solution for the
initial spectrophotometer setting.
1.6 Prepare a calibration curve by plotting the absorbance of the standards
against the copper content in micrograms.
33

PROCEDURE 1. Transfer 200 ml of acidified (with 0.4 ml hydrochloric acid, sp gr 1.19)
and unfiltered sample (for total copper) or 200 ml of filtered (through
0.45 micron filter) and acidified sample (for dissolved copper) into a 250
ml separatory funnel.
2. Add 1 ml of hydroxylamine hydrochloride solution and mix.
3. Add 10 ml of sodium acetate solution and mix.
4. Add 2 to 4 ml of neocuproine solution and shake the funnel and contents
for 1 minute.
5. Add 25 ml of chloroform solvent or isoamyl alcohol, shake vigorously for
at least 1 minute and allow to stand for 5 minutes.
6. Transfer the organic layer into a dry 50 ml Erlenmeyer flask and add 10
ml of isopropyl alcohol to clear the solution. Make upto 35 ml with
chloroform solvent or isoamyl alcohol depending on the extractant used.
7. Measure the absorbance of the organic solution (6.6) at 457 nm (when
chloroform solvent is the extractant) using a mixture of 25 ml of
chloroform solvent and 10 ml of isopropyl alcohol as a reference solution
for initial spectrophotometer setting or at 454 nm (when isoamyl alcohol
is the extractant) using a mixture of 25 ml of isoamyl alcohol and 10 ml
of isopropyl alcohol as a reference solution.
8. Carry out a blank determination on 200 ml of water with all reagents and
extracting in the same manner as for the sample.
CALCULATIONS 1. Calculate the concentration of copper in micrograms per litre in the
sample, as follows:
W x 1000
Copper, micrograms/litre, as Cu = --------------
V
Where:
W = micrograms of copper determined in accordance with sections
5.0 and 6.0.
V = millilitres of sample used.
PRECISION 1. The overall precision of this method may be expressed as follows:
ST = 0.008 X + 0.9
Where:
ST = overall precision.
X = determined concentration of copper, micrograms/litre.
INTERFERENCES 1. None of the ions commonly found in low solids water interfere with the
test.
2. A polythene bottle must be used for sample collection. Hydrochloric acid
(sp gr 1.19) should be added to the filtered sample for total recoverable
copper immediately at the time of collection. The volume of acid should
be sufficient to neutralize the sample to pH 4 (using narrow range pH
paper) and then add 2.0 ml for each litre of sample.
3. Soak all new glassware in hot nitric acid (1+9) for several hours. To
ensure the conditioning of glassware, rinse it with water and run a
copper determination (blank) on copper free water. Repeat until the
copper value is less than 4 micrograms per litre. After carrying out the
test, always rinse the glassware with organic solvent, followed by water.
Always keep the glassware soaked in nitric acid (1+9) until used again.
Discard any glassware that appears etched or scratched.
4. If the sample contains more than maximum concentration of copper
specified in the range, a smaller size sample should be diluted to 200 ml
with copper free water containing 0.4 ml of hydrochloric acid (sp gr 1.19)
per 200 ml of solution.
34

5. Normally, 2 ml of neocuproine solution is sufficient in a test. 4 ml of the
reagent should be used when the sample contains more than 100
micrograms of copper or when it is high in heavy metal ions.
6. The blank determination made for calibration in section 5.0
compensates for copper in both the reagents and 200 ml of water. When
the test water contains less than 10 micrograms/litre of copper, it is
important (in 6.7) to compensate only for the copper in the reagents and
not to include the few micrograms per litre of copper found in copper
free water.
The reagent blank is found, by extracting the copper from two 200 ml
aliquots of copper free water. In aliquot the normal values of reagents in
hydrochloric acid, hydroxylamine hydrochloride, sodium acetate and
neocuproine solution are used and in the other aliquot twice the normal
values of reagents are used. The organic extract from the normal blank
used as reference solution for initial spectrophotometer setting and the
blank obtained from double reagents is measured against the normal
blank. The correct value for copper is found in the unknown sample (6.7)
by subtracting from it the value for the reagent blank.
35

HARDNESS – TOTAL, CALCIUM AND MAGNESIUM
SUMMARY OF METHOD For the determination of total hardness the sample pH is adjusted to 10
with ammonium chloride – ammonium hydroxide buffer solution and
then titrated with EDTA (ethylene diamine tetraacetic acid or its sodium
salt) using Erichrome Black-T as indicator. For calcium hardness
determination the sample pH is adjusted to 12 to 13 with Sodium
Hydroxide and then titrated with EDTA using ammonium purpurate as
indicator. Magnesium is determined by difference.
RANGE 1 to 1000 mg/litre of Ca plus Mg expressed as Ca.
2. Buffer Solution – Dissolve 67.6 g of ammonium chloride in 200 ml of
water. Add 570 ml of ammonium hydroxide (sp gr 0.90) and mix. Add
5.0 g of magnesium salt of EDTA and dilute to 1 litre with water.
3. Sodium Hydroxide Solution (8% w/v).
4. Ammonium Purpurate – Mix thoroughly 1.0g of ammonium purpurate
with 200 g of sucrose.
5. Eriochrome Black-T – Dissolve 0.4 g of Eriochrome Black-T in 100 ml of
water. This solution has a self life of 1 week.
Alternatively a dry powder mixture of 0.5g of Eriochrome Black-T and
100 g of sodium chloride can be used. This mixture has a shelf life of
1 year.
6. Calcium Standard Solution (1ml = 0.4 mg Ca) – Suspend 1.000g of
calcium carbonate (dried at 180o
C for 1 hour) in 600 ml of water and
dissolve with a minimum of dilute hydrochloric acid. Dilute to 1 litre with
water.
7. EDTA standard Solution (0.01M, 1ml = 0.4mg Ca or 0.243mg Mg) –
Dissolve 3.72 g of Na2EDTA dihydrate [dried overnight over Sulphuric
acid (sp gr 1.84) in a desiccator] in water and dilute to 1 litre.
Standardize against standard calcium solution (3.6).
PROCEDURE 1. Total Hardness (Ca plus Mg)
1.1 Pipet 50.0 ml of sample into a titration flask and adjust the pH to 7-10 by
the dropwise addition of ammonium hydroxide (sp gr 0.90).
1.2 Add 1 ml of buffer solution.
1.3 Add 4 to 5 drops of Eriochrome Black T indicator or approximately 0.2g
of powdered indicator.
1.4 Titrate with EDTA standard solution. The end point will be indicted by
colour change from pink to clear blue.
1.5 Record the volume of EDTA solution required in the titration.
1.6 Determine a reagent blank correction by similarly titrating 50.0 ml of
water including all added reagents.
2. Calcium Hardness
2.1 Pipet 50.0 ml of sample into a titration flask and add 1 ml of sodium
hydroxide solution.
2.2 Add 0.2 g ammonium purpurate indicator and mix.
2.3 Titrate with EDTA standard solution. The endpoint will be indicated by
colour change from pink to purple.
2.4 Record the volume of EDTA solution required to titrate the calcium.
2.5 Determine a reagent blank correction by similarly titrating 50.0 ml of
water including all added reagents.
CALCULATIONS
V1 x M x 10,000
1. Total hardness, mg/litre as CaCO3 = -----------------------
V
V2 x M x 10,000
36

2. Calcium hardness, mg.litre as CaCO3 = -----------------------
V
3. Magnesium hardness, mg/litre as CaCO3 = Total hardness, mg/litre as
CaCO3 minus calcium hardness, mg/litre as CaCO3.
Where:
V1 = millilitres of standard EDTA solution required for magnesium
plus calcium (4.1.5) minus the blank determination (4.1.6).
V2 = millilitres of standard EDTA solution required for calcium (4.2.4)
minus the blank determination (4.2.5).
V = millilitres of sample taken.
M = molarity of standard EDTA solution.
PRECISION 1. The precision of this method for calcium (13 to 88 mg/ litre as Ca) may
be expressed as follows:
Sr = 0.006 X + 0.62
So = 0.006 X + 0.51
Where:
Sr = overall precision.
So = single operator precision.
X = determined concentration of calcium, mg/litre as Ca.
2. The precision of this method for magnesium (2.5 to 36 mg/litre, as Mg)
may be expressed as follows:
ST = 0.017 X + 0.85
SO = 0.002 X + 0.70
Where:
ST = overall precision.
SO = single operator precision.
X = determined concentration of magnesium, mg/litre as Mg.
INTERFERENCES 1. EDTA reacts with several metallic ions. The interference due to these
ions can be minimized by addition of hydroxylamine and cyanide. Metal
concentrations as high as 5 mg/litre Fe, 10 mg/litre Mn, 10 mg/litre Cu,
10 mg/litre Zn and 10 mg/litre Pb can be tolerated when hydroxylamine
and cyanide are added.
2. In the titration of total hardness the higher oxidation states of
manganese above 2 reacts rapidly with the indicator to form discoloured
oxidation products. Hydroxylamine hydrochloride reagent is used to
reduce manganese to divalent state. The divalent manganese
interference can be eliminated by addition of one or two small crystals of
potassium ferrocyanide.
3. In the presence of aluminium concentrations in excess of 10 mg/litre, the
blue colour which indicates that the end point has been reached will
appear and then on short standing will revert to red.
4. In the titration of calcium, ammonium purpurate reacts with strontium but
not with magnesium or barium. In the presence of strontium, the
endpoint is slow and the titration is not strictly stoichiometric. Barium
does not titrate as calcium, but affects the indicator in some unknown
way so that no endpoint or a poor endpoint is obtained. Barium can be
removed by precipitation with Sulphuric acid.
2. If total recoverable calcium and magnesium concentration are being
determined, acidify the sample with nitric acid (sp gr 1.42) to a pH of 2 or
less (check with the help of narrow range pH paper) immediately at the
time of collection; normally about 2 ml/litre is required.
3. If dissolved calcium and magnesium concentrations are being
determined, filter the samples through a 0.45 micron membrane filter
and acidify the filtrate with nitric acid (sp gr 1.42), 2 ml/litre.
4. The upper and lower limits of concentration given in range (3.0) may be
extended either by dilution or use of micro apparatus.
37

5. The titration of the sample with EDTA should be completed within 5
minutes of the buffer addition. If more than 15 ml titrant is required, take
a smaller sample aliquot and repeat the test.
6. Fluorescein methylene iminodiacetic acid indicator can be used in place
of ammonium purpurate used in the titration of calcium. The end point
will be indicated by a colour change from deep green to purple.
This indicator is prepared by grinding 0.2g of fluorescein methylene
iminodiacetic acid and 0.12g of thymol-phthalein with 20 g of potassium
chloride to 300 to 425 micron size.
38

HYDRAZINE
(p-Dimethylamino Benaldehyde Method, 4 to 100 micrograms/litre).
SUMMARY OF METHOD The sample is reacted with a solution of para-dimethyl
aminobenzaldehyde to produce a yellow colour. The intensity of the
colour is measured colorimetrically at a wavelength of 458 nm.
RANGE 4 to 100 micrograms/litre N2H4.
APPARATUS 1. Spectrophotometer suitable for measurement at 458 nm.
2. Matched pairs of 10 mm and 50 mm cells.
2. Hydrazine standard solution (1 ml = 100 microgram N2H4) – Dissolve
0.328 g of hydrazine dihydro chloride (N2H4.2HCl) in 100 ml of water and
10 ml of hydrochloric acid (sp gr 1.19). Dilute to 1 litre with water.
3. Hydrochloric Acid (sp gr 1.19).
4. Hydrochloric Acid (1+9) – Mix 1 volume of hydrochloric acid (sp gr 1.19)
with 9 volumes of water.
5. Hydrochloric Acid (1+99) – Mix 1 volume of hydrochloric acid (sp gr
1.19) with 99 volumes of water.
6. Para Dimethylaminobenzaldehyde Solution – Dissolve 4.0 g of p-
dimethylaminobenzaldehyde in 200 ml of methyl alcohol and 20 ml of
hydrochloric acid (sp gr 1.19). Store in a dark bottle, out of direct
sunlight.
CALIBRATION 1. Prepare a series of hydrazine standards by making appropriate dilutions
of the hydrazine solution (1ml = 100 micrograms N2H4) with hydrochloric
acid (1+99), so that a 50 ml aliquot of each dilution will contain the
desired quantity of hydrazine (0.2 to 5.0 micrograms).
2. Pipet 50 ml portions of the hydrazine standard solutions as prepared in
section 5.1 into 100 ml cylinders and proceed in accordance with section
6.0 (6.3 – 6.4).
3. Prepare a calibration curve by plotting transmittance against micrograms
of hydrazine.
PROCEDURE 1. Place 5.0 ml of hydrochloric acid (1+9) into a 100 ml measuring flask.
Collect that sample upto the mark.
2. Transfer the sample, to the cylinder that will contain approximately 0.20
to 5.0 micrograms of hydrazine and make the final volume to 50 ml with
water.
3. Add 10.0 ml of p-dimethylaminobenzaldehyde solution, mix and allow to
stand for 10 minutes.
4. Measure the transmittance of the solution of 458 nm by adjusting the
spectrophotometer at 100% transmittance with the blank, prepared by
adding 10.0 ml of p-dimethylaminobenzaldehyde to 50 ml of water.
CALCULATIONS 1. Calculate the hydrazine concentration in micrograms per litre as follows:
W x 1000
2. Hydrazine, micrograms/litre = --------------
V
Where:
W = micrograms of hydrazine found in accordance with section 6.0.
PRECISION The precision of this method may be expressed as follows:
SO = (0.99 X + 0.041) / V
St = (1.08 X + 0.081) / V
Where:
SO = single operator precision expressed in mg/litre of hydrazine.
St = overall precision expressed in mg/litre. of hydrazine.
X = concentration of hydrazine determined in mg/litre.
39

V = millilitres of sample taken for test.
INTERFERENCES 1. The hydrazine content may be diminished by oxidizing agents collected
with the sample or absorbed by it prior to testing.
2. Colours, that absorb in the prescribed wavelength, also, interfere.
2. The purity of hydrazine dihydrochloride may be checked by iodimetric
methods.
3. Para-dimethylaminobenzaldehyde reagent obtained from different
manufacturers produce different intensities of colour in solution. It is
necessary that each new supply of reagent be tested on standard
solutions before using with previously determined calibration curves.
4. The sample should be analyzed as quickly as possible after collection
since hydrazine undergoes auto-oxidation, as well as, oxidation by
oxidizing agents. Such agents may be in the sample or may enter the
sample from the atmosphere. If it is suspected that oxidation of the
hydrazine in the sample is occurring in the interval between collection
and analysis or if the sample is not to be analyzed immediately then the
sample is to be collected under acid by placing 5.0 ml of hydrochloric
acid (1+9) in a 50 ml volumetric flask, and collecting sufficient sample to
make total volume to 50 ml.
When the sample is collected under acid, the step 6.1 of section 6.0
should be deleted and in step 6.2 hydrochloric acid (1+99) to be used,
instead of water for dilution.
40

IRON
(Bathophenanthroline Method, 200 micrograms/litre and less)
SUMMARY OF METHOD Iron is reduced with hydroxylamine hydrochloride and then reacted with
bathophenanthroline (4, 7-diphenyl – 1, 10 phenanthroline). The red
ferrous complex is extracted with n-hexyl or isoamyl alcohol and the
intensity of the colour is measured at 533 nm.
RANGE 4 to 80 micrograms/litre Fe with 100 mm cell.
10 to 160 micrograms/litre Fe with 50 mm cell.
2. Matched pair of 50 mm and 100 mm cells.
2. Alcohol, n-Hexyl or Isoamyl.
3. Alcohol, Methyl, ethyl or Isopropyl.
4. Bathophenanthroline Solution (0.835 g/litre) – Dissolve 0.0835 g of
bathophenanthroline in 100 ml of ethyl alcohol.
5. Hydrochloric Acid (1+1) – Mix equal volumes of hydrochloric acid (sp gr
1.19) and water.
6. Hydroxylamine Hydrochloride Solution (10%).
7. Iron Standard Solution (1ml = 1 microgram Fe) – Dissolve 0.1000 g of
pure iron in 10 ml of hydrochloric acid (1+1) and 1 ml of bromine water.
Boil to remove excess bromine. Add 200 ml of hydrochloric acid (1+1),
cool, and dilute to 1 litre with water (solution A). To 10 ml of solution A
add 12 ml of hydrochloric acid (1+1) and dilute to 1 litre with water.
8. Hydrochloric Acid (1+9) – Mix 1 volume of hydrochloric acid (sp gr 1.19)
9. Ammonium hydroxide (1+1) – Mix equal volumes of ammonium
hydroxide (sp gr 0.90) and water.
CALIBRATION 1. Prepare a series of standards (at least five concentrations) to cover the
expected range of iron concentrations by diluting appropriate volumes of
Iron standard solution (4.7, 1 ml = 1 microgram Fe) as follows:
1.1 Place the required volumes of Iron standard solution (4.7) in 125 ml
separatory funnels.
1.2 Add water to make 50 ml.
1.3 Add 2.0 ml of hydroxylamine hydrochloride solution and mix.
1.4 Add 3.0 ml of bathophenanthroline solution and shake for 30 seconds.
1.5 Add ammonium hydroxide (1+1) dropwise with mixing until a distinct
turbidity forms. Add hydrochloric acid (1+9) dropwise with mixing until 1
drop clears the solution. Allow to stand for 1 minute.
1.6 Proceed in accordance with section 6.0 (6.5 to 6.8).
1.7 Simultaneously carry out a blank determination containing no added iron
using 50 ml of water and all reagents.
PROCEDURE 1. Transfer a volume of sample (filtered through 0.45 micron membrane
filter) containing not more than 8 micrograms of iron, to a 125 ml
separatory funnel.
2. Add 1.0 ml of hydroxylamine hydrochloride solution and mix.
3. Add 3.0 ml of bathophenanthroline solution and shake for 30 seconds.
4. Add ammonium hydroxide (1+1) dropwise with mixing until a distinct
turbidity forms. Add hydrochloric acid (1+9) dropwise with mixing until 1
drop clears the solution. Allow to stand for 1 minute.
5. Add 15.0 ml of n-hexyl or isoamyl alcohol and shake vigorously for 1
minute. Allow to stand for 15 minutes.
6. Discard the aqueous layer and transfer the alcohol layer into a 25 ml
volumetric flask.
7. Add 10 ml of methyl, ethyl or isopropyl/alcohol to the funnel and wash
the internal surfaces by rolling and tumbling the funnel. Transfer this
41

alcohol into the previous alcohol extract (6.6). Dilute to the 25 ml mark
with the alcohol used for extraction (6.6).
8. Measure the colour of the alcohol solution at 533 nm, adjusting the
spectrophotometer to zero absorbance reading with a reference solution
of 15 ml of alcohol used in step 6.5 and 10 ml of alcohol used in step
6.7.
9. Carry out a blank determination on 50 ml of water, with all reagents and
extracting in the same manner as for the sample.
CALCULATIONS 1. Calculate the concentration of iron in micrograms per litre in the sample
as follows:
W x 1000
Iron, micrograms/litre = -------------
V
Where:
W = micrograms of iron, read from the calibration curve.
V = millilitres of original sample used.
PRECISION 1. The single operator and overall precision varies with the determined
concentration and may be expressed as follows:
SO = 0.008 X + 0.92
St = 0.039 X + 1.47
Where:
SO = single operator precision, micrograms/litre.
St = overall precision, micrograms/litre.
X = determined concentration micrograms/litre.
INTERFERENCES 1. If pH is between 3.3 and 3.7 a 1 mg/litre concentration of the following
ions does not interfere with the test : copper, manganese, aluminium,
zinc, magnesium, sodium, silica, nitrate and orthophosphate.
2. If either dissolved or ferrous iron is to be determined, the sample must
be analyzed as soon as possible after collection. If only total iron is to be
determined, the sample should be immediately acidified with 2 ml of
hydrochloric acid (sp gr 1.19) per 50 ml.
3. Soak all new glassware is hot hydrochloric acid (1+1) for 2 hours. Drain
and rinse at least 3 times with iron free water. Before and after use,
clean all glassware by making an iron extraction of each piece (without
separating the alcohol – water layers). Drain and flush with iron free
methyl alcohol, ethyl alcohol, or isopropyl alcohol.
4. If iron content is high in hydrochloric acid (4.5) causing a high blank,
distil in an all glass apparatus, rejecting the first 50 ml and the last
100 ml of distillate.
5. Hydroxylamine hydrochloride solution (4.6) can be purified as follows:
Adjust pH to 3.5 using a pH meter by dropwise addition of ammonium
hydroxide (1+1) and hydrochloric acid (1+9). Transfer to a separatory
funnel, add 6.0 ml of bathophenanthroline solution and shake. Allow to
stand for 1 minute. Add 20 ml of n-hexyl or isoamyl alcohol and shake
for 1 minute. Allow to stand for 15 minutes. Remove the aqueous layer
and discard alcoholic layer. Repeat extraction by again adding 3 ml of
bathophenanthroline solution and 20 ml of alcohol. Discard the alcohol.
If no further extractions are indicated make an extraction with alcohol
alone and allow to stand for a long time to remove all of the alcohol
layer. Discard the alcohol layer.
6. For total iron determination, heat the sample for 1 hour at 60o
C with
4 ml of hydrochloric acid (1+1) and 2 ml of hydroxylamine hydrochloride
solution. Thioglycolic acid can also be used for solubilising unreactive
iron.
42

ORGANIC MATTER
(Potassium Permanganate Consumption Method)
SUMMARY OF METHOD The sample is reached with a standard solution of potassium
permanganate at 27o
C for 4 hours and the residual permanganate is
determined iodometrically.
RECORDS 1. Water – conforming to specifications Type III.
2. Potassium Permanganate Stock Solution – Dissolve 3.951g of
potassium permanganate (previously dried at 105o
C) in water and dilute
to 1 – litre. Standardize with sodium oxalate. (see notes).
3. Potassium Permanganate Standard Solution (N/80) (1ml = 0.1 mg
oxygen) – Dilute 100 ml of potassium permanganate stock solution (2.2)
to 1 litre.
4. Sulphuric Acid (1+3) – Mix 1 volume of Sulphuric acid (sp gr 1.84) with 3
volumes of water. Add standard permanganate solution until a very faint
pink colour persists after 4 hours.
5. Potassium Iodide.
6. Sodium Thiosulphate Stock Solution – Dissolve 31.2 g of sodium
thiosulphate and 6g of sodium bicarbonate in water and dilute to 1-litre.
7. Sodium Thiosulphate Standard Solution (N/80) – Dilute 100 ml of
sodium thiosulphate stock solution (2.6) to 1-litre. Standardize with N/80
potassium permanganate solution.
8. Starch Indicator Solution – Make a paste of 1g of soluble starch and mix
into 1 litre of boiling water. Add 20g of potassium hydroxide, mix, and
allow to stand for 2 hours. Add 6ml of glacial acetic acid, mix, and add
sufficient hydrochloric acid to adjust the pH to 4.0 (Check with a narrow
range pH paper). This has a shelf life of 1 year.
PROCEDURE 1. Place 100 ml of the sample into a clean, glass stoppered bottle of 250
ml capacity and place in a thermostat at 27o
C.
2. When the temperature of the sample becomes 27o
C, add 4ml of
Sulphuric acid (1+3) and 10ml of potassium permanganate solution
(N/80). Mix well and allow to stand for 4 hours at 27o
C protected from
sunlight.
3. Add few crystals of potassium iodide (0.2-0.3g) and titrate the librated
iodine with standard sodium thiosulphate solution (N/80) using starch
indicator.
4. Run a blank of 100ml of water under the same conditions.
CALCULATIONS 1. Calculate the milligrams of oxygen consumed per litre of sample as
follows:
Oxygen consumed, mg/litre = V2 – V1
Where:
V2 = millilitres of standard sodium thiosulphate used for blank
titration.
V1 = millilitres of standard sodium thiosulphate used for sample
titration.
43

OXYGEN, DISSOLVED
(Indigo Carmine Method, less than 60 micrograms/litre)
SUMMARY OF METHOD Dissolved oxygen reacts, under alkaline conditions, with the indigo
carmine solution to produce a progressive colour change from yellow-
green through red to blue and blue-green. The colour developed in the
sample is compared with colour standards representing different
concentrations of dissolved oxygen.
RANGE Less than 60 micrograms/litre.
APPARATUS 1. Burette, 25 or 50 ml.
2. Sampling Bucket, with an overflow at least 20 mm above the top of the
sampling vessel.
3. Sampling Vessels – Nessler type 60 ml tubes or 300 ml BOD bottles
having a raised lip around the neck and glass stoppers ground to a
conical lower tip.
2. Colour standards, stock solutions.
2.1 Red Colour Standard-Dissolve 59.29g of cobaltous chloride
(CoCl2.6H2O) in hydrochloric acid (1+99) and dilute to 1 litre.
2.2 Yellow Colour Standard-Dissolve 45.05g of ferric chloride (FeCl3.6H2O)
in hydrochloric acid (1+99) and dilute to 1 litre.
2.3 Blue Colour Standard – Dissolve 62.45g of cupric sulphate (CuSO4.
5H2O) in hydrochloric acid (1+99) and dilute to 1-litre.
2.4 Hydrochloric Acid (sp gr 1.19)
2.5 Hydrochloric Acid (1+99)-Mix 1 volume of hydrochloric acid (sp gr 1.19)
2.6 Indigo Carmine Solution-Dissolve 0.18g of indigo carmine and 2.0g of
dextrose (or glucose) in 50ml of water. Add 750 ml of glycerin and mix
thoroughly.
2.7 Indigo Carmine-Potassium Hydroxide Reagent-In a small bottle mix 4
parts by volume of indigo carmine solution (4.2.6) with 1 part of
potassium hydroxide solution (4.2.8). Allow to stand until the initial red
colour changes to lemon yellow. Prepare fresh solution daily.
2.8 Potassium Hydroxide Solution (530g/litre)- Dissolve 530g of potassium
CALIBRATION 1. Prepare a series of colour standards as listed below:
EQUIVALENT DISSOLVED
OXYGEN (micrograms/litre)
MILLILITRES OF COLOUR STANDARDS
RED YELLOW BLUE
0 0.75 35.0 -
5 5.0 20.0 -
10 6.25 12.5 -
15 9.4 10.0 -
20 13.0 6.4 -
25 14.4 3.8 -
30 14.6 3.3 0.2
35 15.1 2.9 1.1
40 15.5 2.4 2.2
45 16.1 2.0 2.8
50 18.3 1.7 8.1
55 21.7 1.4 13.1
60 25.0 1.0 15.0
44

2. Place the amounts of stock solutions listed above in 300 ml borosilicate
glass stoppered reagent bottles. Add 3.0 ml of hydrochloric acid (sp gr
1.19) to each. Dilute to neck of the bottle with water. Stopper and mix by
inversion. Store in a dark place.
PROCEDURE 1. Place a clean sampling vessel in the sampling bucket and collect the
sample under water. Allow the sample to overflow for several minutes.
2. Fix a burette such that its tip dips into the overflowing sample to a depth
of 10 to 15 mm.
3. Fill the burrette with indigo carmine-potassium hydroxide reagent. Drain
about 1ml of reagent into the overflowing sample, and allow the sample
to flush for 1 minute.
4. Remove the sample tubing from the sampling vessel.
5. Quickly introduce 0.8ml of the reagent if 60 ml tube is used or 4ml of
reagent if a BOD bottle is used, stopper the vessel and mix by inversion.
6. Place the vessel on a white surface and match its colour with the
standard by viewing at a 45o
angle using a ‘Cool’ white fluorescent lamp
for illumination.
PRECISION 1. The single operator precision of this method may be expressed as
follows:
SO = 0.052 X + 0.7
Where:
SO = single operator precision
X = concentration of dissolved oxygen determined, micrograms/litre.
INTERFERENCES 1. Tannin, hydrazine, and sulphate do not interfere up to 1 mg/litre.
2. Ferric iron, cyclohexylamine, and morpholine up to 4 mg/litre can be
tolerated.
3. Ferrous iron will produce low results and copper will cause high results.
4. In samples, where ferrous iron and copper are present, their combined
effect is frequently zero.
5. Nitrate is a possible interference.
2. All colour stock solutions should be stock in coloured bottles to prevent
fading.
3. Indigo carmine solution (4.2.6) is stable for 30 days if stored in a
refrigerator.
4. In the procedure (6.1), the sample flow should be between 500 to 1000
ml/minute when using 300 ml bottle, or 100 to 200 ml/minute when using
60 ml sample tubes.
5. In the procedure (6.6), the colours should be matched as soon as
possible after mixing the reagents and sample, since the colours are not
stable for more than 30 minutes and air leakage may cause a change in
colour.
6. The sample should be analysed as soon as possible after the collection.
45

OXYGEN DEMAND, BIOCHEMICAL
(Dissolved Oxygen Loss Method)
SUMMARY OF METHOD The sample is incubated at 20o
C for 5 days. Dissolved oxygen is
measured initially and after incubation. The BOD is computed from the
difference between initial and final dissolved oxygen (DO).
APPARATUS 1. Incubation Bottles - 250 to 300 ml capacity with ground glass stoppers.
2. Air Incubator – thermostatically controlled at 20+10
C. All light should be
excluded to prevent possibility of photosynthetic production of DO.
REAGENTS 1. Dilution Water – Add 0.3 g of sodium bicarbonate per litre of Type II
water.
PROCEDURE 1. Adjust the temperature of a suitable portion of the well mixed sample to
20o
C. Remove the oxygen or excess air by maintaining the sample
under vacuum for 10 minutes using laboratory vacuum pump.
2. Fill completely two incubation bottles (250 or 300 ml capacity) with the
sample as treated above (4.1). Allow to stand for 15 minutes.
3. Determine the dissolved oxygen in one bottle by the Iodometric method
and in the other after 5 days incubation in darkness in the stoppered
bottle at 20o
C.
CALCULATIONS 1. Calculate the BOD of the sample as follows:
Bichemical oxygen demand (BOD), mg/litre = D1 – D2
(5 days at 20o
C).
Where:
D1 = initial dissolved oxygen content, mg/litre.
D2 = dissolved oxygen content after 5 days incubation, mg/litre.
INTERFERENCES 1. Samples for BOD analysis may degrade significantly during storage,
resulting in low BOD values. This can be minimized by analyzing the
sample promptly or cooling it to 4o
C or below.
Analysis should be done before 24 hours after grab sample collection.
NOTES 1. The dissolved oxygen content of the sample before incubation shall be
approximately 9 mg/litre or preferably less.
2. For samples of doubtful purity, the sample should be mixed with dilution
water in the ratio 1:1 at 20o
C. Further dilutions shall be used if necessary
to ensure that not more than half the oxygen is consumed during the
incubation. Determine the dissolved oxygen before and after incubation
and calculate the result using the appropriate dilution factor.
46

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