Flame photometric analysis, Instrumentation, Detectors, Applications

1. Presented BY-:
-Prajkta Jambhale
-Sanika Varde
[B.Pharmacy]

2. • During 1980s Bowling Barnes, David Richardson,
John Berry and Robert Hood developed an
instrument to measure the low concentrations of
sodium and potassium in a solution.
• The principle of flame photometer is based on
the measurement of the intensity of emitted
light when a metal is introduced into the flame.
• The wavelength of the colour tells what the
element is (qualitative).
• and the colour’s intensity tells us how much the
element is present (quantitative).
Introduction

3. Principle
• When a solution of metallic salt is sprayed as
fine droplets into a flame.
• Due to the heat of the flame, solvent in
droplets vapourised leaving a fine residue of
salt.
• The salt is converted into the gaseous state.
• This gaseous molecules converts into neutral
atoms i.e atomization .
Conti..

4. • Due to the thermal energy of the flame, the
atoms get excited. The excited atom are
unstable, therefore quickly return to ground
state.
• In this process of return to ground state, excited
atoms emit radiation of specific wavelength. This
wavelength of radiation emitted is specific for
every element.
• This specificity of the wavelength of light
emitted makes it a qualitative aspect. While the
intensity of radiation depends on the
concentration of element. This makes it a
quantitative aspect.

5. VAPOURISATION
EXCITATION
ATOMIZATION
TRANSFORMATION

6. When solution of Calcium Chloride is sprayed into the flame
following steps occurs
CaCl2
( Solid )
CaCl2
(Gas)
Ca
(g)
Cl2
(g)
Ca
ionization excitation
‘O’ from
gases
‘OH’ from
gases
flame
Ca+
(Ion)
Ca0
(neutral atom)
CaOH
(g)
CaO
Example :-

7. Basic Concept
The emitted radiation is calculated by the following equation:
Where,
E2 is the higher level energy;
E1 is the lower level energy;
h is Planck's constant;
v is the frequency of emitted radiation which is defined as-
By substituting the ‘ν’ value in the above equation
Therefore, From the above equation, we can calculate the
wavelength of the emitted radiation.
E2 – E1 = hv
E2 – E1 = hc / λ
Conti..

8. In the case of the atoms, the population of any excited state
relative to that of the ground state is given by the following
equation which is known as Boltzmann equation.
Where
• N* = the number of atoms in excited state
• N0 = the number of atoms in ground state
• −ΔE = energy difference between ground and excited state
(in J);
• k = Boltzmann constant (=1.28 × 10−23 J k−);
• T = absolute temperature.
• g* and g0 are the statistical factors that depend on the
degeneracies of the levels involved.
Conti..

9. The intensity of the light emitted could be
described by the Scheibe–Lomakin equation:
where
• c is the concentration of the element;
• k is the constant of proportionality;
• n ~1 (at the linear part of the calibration curve),
therefore,
the intensity of emitted light is directly
proportional to the concentration of the sample.
I = k×cn

10. Characteristic Wavelength & Its Color

11. Flame Emission Spectrophotometry Atomic Absorption Spectrophotometry
Amount of light emitted by the
excited atom is measured
Amount of light absorbed by ground
state atom is measured
Intensity of emitted radiation is
directly proportional to the number of
atoms in excited state.
Intensity of absorbed radiation is directly
proportional to the number of atoms in
ground state
Here excitation process and signal
response is influenced by flame
temperature.
Here absorption intensity and signal
response is independent to temperature.
Beer’s law is not obeyed. Beers law is obeyed over wide range of
concentration
Relationship between emission
intensity Vs concentration in not that
much linear.
Absorption intensity Vs concentration is
very much linear.
Absence of the light source Presence of a light source ( HCL )
Differences Between Atomic Absorption Spectrophotometry
And Flame Emission Spectrophotometry:

12. Structure Of Flame
The flame may be divided into the
following regions or zones-:
A. Preheating zones
B. Primary reaction zone/inner zone
C. Internal zone
D. Secondary reaction zone
D
A
C
B

13. A. Preheating Zone-
In this, combustion mixture is heated to the ignition
temperature by thermal conduction from the primary
reaction zone.
B. Primary Reaction Zone-
-This zone is about 0.1 mm thick at atmospheric
pressure.
-There is no thermodynamic equilibrium in this zone.
- The Concentration of ions and free radicals is very high.
-This zone is not used for flame photometry.
Zones Of Flame
Conti..

14. C. Interconal Zone –
-It can extend up to considerable height.
-The maximum temperature is achieved just above the
tip of the inner zone.
-This zone is used for flame photometry.
D. Secondary Reaction Zone –
In this zone, the products of the combustion processes
are burnt to stable molecular species by the
surrounding air.

15. Burners
Several kinds of burners are used to convert the fine droplets of
sample solution into neutral atom, which further due to the high
heat or temperature of flame are excited hence emit radiation of
characteristic wavelength and colour.
Types Of Burner :
1. Mecker burner
2. Total consumption burner
3. Premix burner
4. Lundergarph’s burner
5. Shielded burner
6. Nitrous oxide – Acetylene burner 20

16. Requirement Of Flame
• It should have proper temperature
• Temperature should remain constant throughout the
operation
• There should not be any fluctuation during burning
Function Of Flame
• To convert the analyte of the liquid sample into vapour
state
• To decompose the analyte into atoms and simple
molecules
• To excite the formed atoms/free atoms/simple molecules
to emit radiant energy

17. FUEL OXIDANT THEPERATURE
TOWN GAS AIR 1700 o C
PROPANE AIR 1900 o C
BUTANE AIR 1925 o C
ACETYLENE AIR 2200 o C
TOWN GAS OXYGEN 2700 o C
PROPANE OXYGEN 2800 o C
BUTANE OXTGEN 2900 o C
ACETYLINE NITROUS OXIDE 2955 o C
List of Fuel and Oxidant Used

18. 1. Mecker Burner
• This was the primitive type of burner used in
flame photometry and was used earlier.
• It generally works with aid of natural gas and
oxygen as fuel and oxidant.
• The temperature so produced in the flame
was relatively low, resulting in low excitation
energy.
• Now a days it is not used but it was best
suited for alkali metal.

19. 2. Total Consumption Burner
• Due to the high pressure of fuel and oxidant the
sample solution is aspirated through capillary .
• As soon as liquid sample drawn into the base of
flame oxygen aspirates sample solution leaving
solid residue. Atomization and excitation then
occurs.
• Hydrogen and oxygen are generally employed as
fuel and oxidant.
Conti..

20. Advantage
-Entire consumption of sample
Disadvantage
-production of non uniform flame and turbulent.
-noisy

21. 3.Premix Of Laminar Flow Burner
• In this burner the sample , fuel oxidant are thoroughly
mixed before aspiration and reaching to flame.
• Gases move in non turbulent fashion i.e. Laminar flow.
• Only small portion (about 5%) of the sample in the form
of small droplet reaches the flame and is easily
decompose.
Conti..

22. Advantage
-Uniform flame produced
-efficient atomization takes place
-noiseless
-non turbulent
-stable
Disadvantage
1. heavy loss of mix up to 95%.
2. Smaller number of atom reaches the flame -> reduces the
emission intensity -> Give incorrect result .
3. If the sample contain two solvent. More volatile will
evaporates -> leaving the sample in the form of
undissociated atoms in the less volatile solvent.

23. 4. Lundengarph’s Burner
• The sample must be in liquid form.
• A small sample liquid droplets vaporized and move to base of
flame in the form of cloud .
• Large droplets condensed at side and then drained off.
Advantage
-Physically quiet to
operate
Disadvantage
-small portion (about 5%) of the sample reaches the flame.
-The rest of the droplets condense and are drained away.
This leads to significant loss in atomization efficiency and
therefore sensitivity.

24. Mirrors
• The radiation emitted by the flame is generally
towards all the direction.
• Hence, a mirror is place behind the flame
• It focus the radiation towards the entrance
slit of the monochromator.
• A concave mirror is used as it is front faced
reflecting type

25. Monochromators
The main of the monochromator is to convert
polychromatic light into the monochromatic light.
Two types of monochromator can be used:
1. Prism : Quartz material is used for making prism,
as quartz is transparent over entire region.
2. Grating : it employs a grating which is essentially
a series of parallel straight lines cut into a plane
surface.

26. Detectors
• Detector is device which converts light energy
into electrical signals that are displayed on read
out device.
• The emitted radiation falls on the detector which
determines the intensity of radiation emitted by
sample.
• Types -:
• Photomultiplier tube
• Photo emissive cell
• Photo voltaic cell

27. 1. Photomultiplier Tube
• Photomultiplier tube is generally used as
detector in flame photometry.
Conti..

28. Construction
• It consist of an evacuated tube which contains one
photo-cathode and 9 to 16 electrodes knows as
dynodes.
• The surface of dynode is Be-Cu, Cs-Sb or similar
material.
• The photo cathode surface is of alkali or alkali metal
oxide.
• Dynode D1 is maintained at a voltage approximately
90V more positive than Cathode and electrons are
accelerated towards it as a result. Dynode D2 is 90V
more positive than dynode D1.
Conti..

29. Working
• Radiation striking the photosensitive cathode give rise to
photoelectrons by photoelectric effect.
• Dynode D1 is held at positive voltage with respect to the
photocathode. The electrons emitted by the cathode are
attracted to the first dynode D1 and accelerated in the field.
• Each electron striking dynode D1 thus give rise to two to
four secondary electrons. These are attracted to dynode D2
which is again positive with respect to dynode D1.
• By the time this process has been repeated 9 times, 10*6 to
10*7 electrons have been formed for each incident photon.
• This cascade electrons is finally collected at anode and
resulting current is then converted to voltage and measured.

30. 2.Photo Emissive Cell
Construction
• It consist of an evacuated tube which contains
1.semi cylindrical photocathode of metal
2.wire anode.
• The concave surface of cathode supports a layer of photo
emissive material which emits electrons when irradiates with
light of suitable energy.
Conti..

31. Working
• Radiation striking the semi-cylindrical
photosensitive cathode give rise to
photoelectrons by photoelectric effect
• These are attracted and collected by an anode i.e.
electrons flow to wire anode and photocurrent
result.
• The current which is created between the
cathode and anode is regarded as measure of
radiation falling on the detector.

32. 3. Photovoltaic Cell
• It has a thin metallic layer coated with silver or gold act as
electrode , also has metal base plate which act as another
electrode.
• Two layers are separated by semiconductor layer of selenium,
when light radiation falls on selenium layer.
• This creates potential difference between the two electrode
and cause flow of current

33. Instruments
(First Type & Second Type)
Working-:
1. Total consumption burner and premix burner can be used.
2. A collimating mirror to increases the emission intensity.
3. The sample solution is sucked by atomizer
4. Then flame solution is aspirated into flame in the form of a fine
spray.
First Type
Conti..

34. 5. Spectral emission comes from the excited
atom formed during the process of
combustion in flame.
6. The emitted radiation is collected by a
collimating concave mirror from the flame
and is then permit through a prism and slit.
7.The radiation strikes a photo detector and the
magnitude of the electrical signal developed
is read out on a meter.

35. Second Type Or Internal Standard Flame
Photometer
1. Lithium is used as an internal standard and an equal
concentration is added to the standard and sample
solution.
Conti..

36. 2. The sample solution containing lithium is sucked by an
atomizer and fine particle are fed into flame.
3. The emitted radiation is collected by a mirror through a
filter.
4. The emitted radiation from the mirror is divided into two
parts.
5. First part due to lithium and second part due to
presence of element to be observed.
6. Both parts are received by separate amplifier and
intensity of element detect by common detector.
This photometer has advantage over first type photometer.
Its remove the effect of momentary fluctuations caused by
fluctuations in fuel and oxidant pressure in flame
characteristics.

37. Interferences
• In determining the amount of a particular element present,
other elements can also affect the result.
INTERFERENCES
Spectral
interferences
Ionic
interferences
Chemical
interferences
Cation-anaion
interference
Cation-cation
interference
Conti..

38. 1.Spectral Interferences:
• occurs when the emission lines of two elements cannot
be resolved or arises from the background of flame itself.
• They are either too close, or overlap, or occur due to high
concentration of salts in the sample
2. Ionic Interferences:
• high temperature flame may cause ionisation of some of
the metal atoms.
• e.g. sodium.
• The Na+ ion possesses an emission spectrum of its own
with frequencies, which are different from those of
atomic spectrum of the Na atom.
Conti..

39. 3.Chemical Interferences:
The chemical interferences arise out of the reaction between
different interferents and the analyte.
Includes:
• Cation-Anaion Interference:
• The presence of certain anions, such as oxalate, phosphate,
sulfate, in a solution may affect the intensity of radiation
emitted by an element.
• E.g., calcium + phosphate ion forms a stable substance, as
Ca3(PO4)2 which does not decompose easily, resulting in the
production of lesser atoms
• Cation-Cation Interference:
• These interferences are neither spectral nor ionic in nature .
• Eg. aluminum interferes with calcium and magnesium
Conti..

40. Applications Of Flame Photometry
• Qualitative applications:
–Used for the determination of alkali and the
alkaline earth metals in samples which are
easily prepared as aqueous solutions.
–Example: Sodium produces yellow flame.
–Non-radiating element such as carbon,
hydrogen and halides cannot be detected.
Conti..

41. • Quantitative applications:
1. The concentration of various alkali and alkaline
earth metals is important in determining the
suitability of the soil for cultivation.
2. Used for the determination of the concentration of
sodium and potassium ions in body fluids since their
ratio controls the action of muscles including the
heart.
3. Analysis of water from various sources is carried out
to determine its suitability for drinking, washing,
agricultural and industrial purposes.
4. Used for determination of lead in petrol.
Conti..

42. 5. Analysis of soft drinks, fruit juices and alcoholic
beverages can also be analyzed by using flame
photometry.
6. The calibration curve is prepared by measuring the
intensity of emission for a series of solutions of different
concentrations prepared by using a standard solution.
Plotting a graph between emission intensity and
concentration of the ionic species of the element of
interest.
The concentration of the element in the unknown
sample can then be found out from the standard plot as
is done in visible spectrophotometry.
Conti..

43. a
• very low concentration range.
• In this emission falls below expected value due to ionisation as
some atoms are converted to ions.
• For example, the ionisation of potassium is as given below:
• K K++ + e-
• Such ionisation is, however, insignificant at higher concentration.
b
• linear region
• Used for quantitative
measurements.
c
• high concentration
• Negative deviation is observed due to self-absorption.
• Photons emitted by the excited atoms are partly
absorbed by ground state atoms in the flame.
Standard plot

44. • If the samples contain high and variable
concentrations of matrix materials, or when the
samples contain solids, then effect on absorption is
hard to duplicate.
• In such cases, the following two methods are
employed:
1.Standard addition method.
2.Internal standard method.
Conti..

45. 1. Standard Addition
Method:
1. In this method, known amount of a standard
solution is added to identical aliquots of the
sample and the absorbance is measured.
2. The first reading is the absorbance of sample
alone and the second reading is absorbance of
sample containing analyte plus, a known amount
of analyte and so on. Conti..

46. 3. Similarly, in flame photometric determinations,
increasing amounts of a standard solution of
the salt of the element to be determined are
added to a series of solutions of the sample.
4. The intensity of emission for all these solutions
is then measured.
5. A curve of intensity versus concentration of
the added element is obtained and
extrapolated to zero value of intensity to give
concentration of the element in the sample

47. 2. Internal Standard Method:
1.In this method, a constant amount of another
metal which is not present in the sample is
added to both the unknown sample and a series
of standard solutions of the element be
determined. This is called internal standard.
2.for example, lithium is added in the
determination of sodium metal.
Conti..

48. 3.Since both the element and the internal standard
are in the same solution, the emission readings at
the wavelengths of both the internal standard
and the element to be enclosed are
simultaneously determined.
4. The intensity ratio for the two elements is then
plotted against concentration of the standard
solution.
5. From the observed ratio for the sample, the
concentration of the element in it can be
determined.

49. Merits And Advantages
MERITS
• The sensitivities of the flame photometry for most
alkali and alkaline earth metals lie in the ppm and
sub-ppm range
• Flame photometry is also successful in determining
certain transition elements such as copper, iron and
manganese.
ADVANTAGES
• It is a simple, relatively inexpensive, high sample
throughput method used for clinical, biological, and
environmental analysis.

50. Limitations
• As natural gas and air flame are employed for the
excitation, the temperature is not high enough to excite
transition metals, therefore the method is selective
towards detection of alkali and alkaline earth metals.
• The low temperature renders this method susceptible to
certain disadvantages, most of them related to
interference and the stability of the flame and aspiration
conditions.
• Fuel and oxidant flow rates and purity, aspiration rates,
solution viscosity, affect these.
• It is therefore very important to measure the emission
of the standard and unknown solutions under identical
conditions.
Conti..

51. • Only liquid samples can be used. In some cases,
lengthy steps are necessary to prepare liquid
samples.
• Though this technique measures the total metal
content present in the sample, it does not
provide the information about the molecular
structure of the metal present in the sample.
• It is difficult to obtain the accurate results of ions
with higher concentration.

52. Reference
• Gurudeep R.Chatwal, Sham K. Andand, Instrumental
Methods of Chemical Analysis, Fifth revised & enlarged
edition, Reprint 2017, Pg No: 2.367- 2.388, Himalaya
Publishing House.
• BK Sharma,Instrumental Methods of Chemical Analysis,
Thirtieth Edition, 2015, Pg No: 421-454, Goel Publishing
House
• Keith Wilson & John Walker, Practical Biochemistry,
Principles & Techniques, Cambridge low-price editions, 5th
Edition, Chapter: Spectroscopic Techniques, Pages : 486-
490. Published by Cambridge University Press.
• https://www.hindawi.com/journals/jchem/2013/465825/
• http://rxpharmaworld.blogspot.com/2016/12/flame-
photometry.html