11 kf-theory jntu pharmacy
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KF TITRATION
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11 kf-theory jntu pharmacy
- 1. 1 BY Dr. Suman Pattanayak Associate Professor Department of Pharma Analysis & QA. Vijaya Institute of Pharmaceutical Sciences for Women M. Pharm/ I Sem Advance Pharmaceutical Analysis
- 2. 2 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF Titration • Coulometric KF Titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF Instruments
- 3. 3 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF titration • Coulometric KF titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF instruments
- 4. 4 KF TitrationKF Titration Method for water determinationMethod for water determination • in technical products (oil, plastics and gases) • in cosmetic products • in pharmaceutical products • in food industry
- 5. 5 KF TitrationKF Titration The KF reactionThe KF reaction I. CH3OH + SO2 + RN [RNH]SO3CH3 II. H2O + I2 + [RNH]SO3CH3 + 2RN [RNH]SO4CH3 + 2[RNH]I (RN = Base)
- 6. 6 KF TitrationKF Titration Basic ingredients of KF reagentsBasic ingredients of KF reagents I2 SO2 Imidazole Methanol Iodine Sulphur dioxide Buffer Solvent
- 7. 7 KF TitrationKF Titration pH dependencypH dependency 0 2 4 6 0 2 4 6 8 10 12 log K pH Optimum: pH range between 5 and 7
- 8. 8 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF titration • Coulometric KF titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF instruments
- 9. 9 KF TitrationKF Titration KF titration methodsKF titration methods Volumetric KF titration Coulometric KF titration Working medium & titrant Iodine is generated in titration cell (anodic oxidation)
- 10. 10 KF TitrationKF Titration Volumetric KF titration step by stepVolumetric KF titration step by step • Fill titration vessel with solvent • Pretitration with KF reagent • Add the sample • Titrate with KF reagent
- 11. 11 KF TitrationKF Titration Volumetric KF reagentsVolumetric KF reagents One component reagents – Titrant contains iodine, sulphur dioxide, buffer and methanol/ethanol – Working medium contains only the methanol/ethanol – Disadvantage: the titre decreases 5% per year in the closed bottle! Two component reagents – Titrant contains iodine – Solvent contains buffer and sulphur dioxide – Advantages: pH optimum in the solvent / fast reaction / titre is very stable
- 12. 12 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF titration • Coulometric KF titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF instruments
- 13. 13 KF TitrationKF Titration Coulometric KF titration step by stepCoulometric KF titration step by step • current is our burette • iodine is produced from a iodide containing solvent by anodic oxidation • generating current is switched off as soon as a slight excess of free iodine is present • free iodine is indicated by a double platinum electrode H+ H II- - - +-
- 14. 14 KF TitrationKF Titration Coulometric KF titrationCoulometric KF titration Cell with diaphragm Cell without diaphragm
- 15. 15 KF TitrationKF Titration How to fill coulometric cell with diaphragm?How to fill coulometric cell with diaphragm? • CatholyteCatholyte 5 mL5 mL Reduction: 2 HReduction: 2 H++ +2 e+2 e-- = H= H22 change catholyte weekly!change catholyte weekly! • Anolyte:Anolyte: about 100 mLabout 100 mL 2 I2 I-- = I= I22 + 2 e+ 2 e--
- 16. 16 KF TitrationKF Titration Comparison with and without diaphragmComparison with and without diaphragm Without diaphragm With diaphragm Recommendable for most applications, sample should have a good solubility in alcohol Reagents with low conductivity (the addition of chloroform or xylene > 10%), with ketone reagents absolute water content < 50 ppm Generator I: 400 mA Generator I: auto
- 17. 17 KF TitrationKF Titration Coulometric KF reagentsCoulometric KF reagents • Capacity of more than 1000 mg of water (100 mL KF reagent) • Anodic and cathodic reagents • Combined reagents • Special reagents for ketones
- 18. 18 KF TitrationKF Titration • Volumetric titration range of application 0.1 % - 100 % depends on sample size • Coulometric range of application 0.001 % - 1 % (10 µg - 200 mg absolute water content), mainly liquids and gases Which is the right method for myWhich is the right method for my application?application?
- 19. 19 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF titration • Coulometric KF titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF instruments
- 20. 20 KF TitrationKF Titration Endpoint indicationEndpoint indication Bivoltametry Ipol = 50 uA Constant current applied to double Pt electrode During titration: Excess H2O High voltage between Pt wires At end of titration: Small excess of free iodine Voltage decreases sharply
- 21. 21 KF TitrationKF Titration Endpoint indicationEndpoint indication
- 22. 22 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF titration • Coulometric KF titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF instruments
- 23. 23 KF TitrationKF Titration permanent consumption of KF reagentpermanent consumption of KF reagent DriftDrift Aim: constant and low drift Optimal: Volumetry <10 µL/min Coulometry 2...10 µg/min • Influence on the results drift correction
- 24. 24 KF TitrationKF Titration DriftDrift • Start drift – acceptable drift value for start of determination (cond. OK) • Stop criteria drift – absolute or relative drift value - Absolute drift– the entered value is the stop drift - Relative drift – the stop drift is calculated from the measured drift value (start) and the entered value
- 25. 25 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF titration • Coulometric KF titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF instruments
- 26. 26 KF TitrationKF Titration Titration parameterTitration parameter VolumetryVolumetry EP at U 250 mV Dynamics 100 mV Stop criteria drift/time Stop drift 20 uL/min Delay time 10 s I(pol): 50 uA CoulometryCoulometry EP at U 50 mV Dynamics 70 mV Stop criteria drift/rel drift Stop drift 5 ug/min Rel. Drift 5 ug/min Start drift 20 ug/min I(pol) : 10 uA
- 27. 27 KF TitrationKF Titration TopicsTopics • KF reaction • Volumetric KF titration • Coulometric KF titration • Endpoint indication • Drift as second endpoint indication • Parameters • KF instruments
- 28. 28 KF TitrationKF Titration Volumetric KF Titration Titrinos: 787 KF Titrino 795 KFP Titrino Titrandos: 841 Titrando PC Control / tiamo Touch Control
- 29. 29 KF TitrationKF Titration Volumetric KF TitrationVolumetric KF Titration Modi 841 Titrando KFT X SET X Meas X
- 30. 30 KF TitrationKF Titration Only a version with dosing units ? • Advantages: The dosing unit can be totally emptied that means: – No crystallisation in cock and tubings – Rinsing the buret several times after changing the titrant is no longer necessary
- 31. 31 KF TitrationKF Titration Coulometric KF titrationCoulometric KF titration 756 Coulometer – with internal printer 831 Coulometer
- 32. 32 KF TitrationKF Titration Coulometric cell Vial placed in the oven Principle of the oven techniquePrinciple of the oven technique
- 33. 33 KF TitrationKF Titration 832 Thermoprep832 Thermoprep 774 Oven Sample774 Oven Sample ProcessorProcessor
Hinweis der Redaktion
- In addition to determination of pH, weighing, acid-base titration, determination of water-content is one of the most frequently used methods in laboratories world wide. In 1935 KF published his “New Method for the Determination of water…”. Many chemists have since been occupied with this reagent. It is used in various industries, from quality control of raw materials to water determination in pharmaceutical products.
- SO2 + ROH -&gt; ester, which is neutralized by the base. Anion of alkyl sulphurous acid = reacting compound, already present in the KF reagent. Titration: Oxidation SO32- -&gt; SO42- by I2, consumes water. Stoichiometric reaction suitable ROH to esterify SO2 completely Suitable base for complete neutralization pH 5-7 preferred (optimized by imidazole) pH adjustment of prime importance =&gt; reaction rate is constant Reaction only takes place as long as sample releases water
- Reagents needed to carry out KFT Water comes from the sample, other components of reaction from reagent
- &lt; pH 5: log K increases linearly with pH reaction rate to low (low results) 5.5-7: optimum, reaction rate constant &gt;8:reaction rate increases slightly (side reactions probably occur)
- Volumetric -&gt; classical titration, I2-containing titrant is added via buret Coulometric -&gt; titrant is produced from I- in solution by anodic oxidation H20 calculated out of applied current Both methods: -titration cell as impervious as possible (atmospheric water!) -water adhered to wall of cell -&gt; removed by swirling conditioned solvent
- Volumetric Higher (absolute) water contents Solid or pasty samples can be directly introduced Variety of suitable solvents, specifically adapted Lower detection limit (50-100 ppm) No stable titre -&gt; determination of titre regularly Why pretitration? O-ring and molecular sieve -&gt; change regularly (in general 6 weeks, depends on air-humidity)
- Two possibilities for working medium and titrant 1-Component: flexibility regarding solvent additives for improving solubility of sample Titrant 5 mg/mL:5 mg H2O can react with 1 mL Titre determination:Water Std 10 recommended, Na-tartrat not as reproducible (bad solubility in methanol) dest water possible, but very tiny amount, good practice needed
- Not a classical titration -&gt; “electronic buret” Same chem. process as volumetric KFT: 1 H2O consumes 1 I2 I2 generated electronically -&gt; absolute method -&gt; no titre Instrument measures time + current flow to EP -&gt; prop. I2 -&gt; prop. H2O Primarily for small amounts of water Metrohm: 10 g – 200 mg H2O, resolution 0.1 g
- I2 produced by generator electrode, 2 different types: Cell without diaphragm - easy to handle and clean - only 1 reagent (!!!Use only reagents intended for these electrodes!!!) - electrode rapidly ready for use (no water on diaphragm) - no cathode compartment -&gt; reduction on Pt plate b) Cell with diaphragm - ketones/aldehydes in sample (special reagents available only for this type) - reagents with low conductivity - lower trace range
- Reagents anolyte -&gt; titration vessel catholyte -&gt; cathode compartment same level of both (prevents pressure compensation) EP: double Pt electrode Absolute -&gt; no titre determination Check from time to time with certified standard
- With diaphragm low water content, conductivity Anode + cathode compartment separated to avoid interferences Allows application of lower current densities of 100-200 A
- 2 reagent solutions necessary for cell with diaphragm: anolyte: modified KF reagent, containing I- instead of I2 KF reaction occurs in anolyte catholyte: enables counterpart cathode reaction which must proceed so that the by-products of the KF-reaction produced at the cathode are not disturbed Combined reagents: Merck reagents and Coulomat E, in both compartments same solution Keton reagents &lt;- side reactions
- Ipol: Small current is applied to between the electrodes (AC much more sensitive than DC) and resulting voltage is measured. As long as there is H2O-&gt; high voltage is applied (I2 -&gt; I-) End of titration: reaction turnover is decreasing (small excess of free I2) -&gt; strong decrease of voltage EP is determined by entering switch-off voltage. Reagent addition stops when reached
- Voltage: High as long as H2O in sample + I2 added Once reaction turnover decreases, potential decreases End point is not sufficient as criteria (titration would stop at signal at 88 sec) -&gt; Additionally drift as EP criteria Drift &lt;- water entering system
- Drift correction: 20 ug/min drift and 1 min measurement, Sample 10 ug =&gt; 30 ug =&gt; correction necessary Drift higher than sample -&gt; lower drift recommended for trace analysis Optimal drift is for europe, depends on humidity, air condition might be good in some countries for trace analysis
- Standard parameters Dynamics:near to EP -&gt; add smaller amount Dynamics 100: from 350 smaller steps (volumetry), 120 (coulometry) Special parameters: Coulometer:Ketone reagents Volumeter:Ethanol reagents
- High-end titrator for up to four 800 Dosino dosing systems. Karl Fischer titration (KFT) and endpoint titration (SET), pH measurement (MEAS), liquid handling. With four MSB connections, one measuring interface; USB connection.
- Direction downwards -&gt; no air-bubbles dosed Possibility to empty totally -&gt; saves reagents
- Work relatively precisely Both available with generator electrodes with or without diaphragm Differences: Printer included 756 Optional: Automatic reagent changer (after a defined time)
- Many substances release water slowly or at elevated temps -&gt; not suitable for direct KFT Further problem: low solubility of sample in alcohol, side reactions of other substances =&gt; Substance heated in oven, locate upstream from cell Released water is transferred by flow of dry carrier gas to titration cell, where KFT takes place =&gt; Only water enters cell =&gt; No unwanted side reactions + matrix effects and contaminations
- Oven for volumetric and coulometric KFT 832 -&gt; stand alone 774 -&gt; automated