Karl fischer.

Water Determination by Karl Fischer Titration

Peter Bruttel Regina Schlink

Water Determination by Karl Fischer Titration

Peter Bruttel Regina Schlink

All rights reserved, including translation rights. Printed in Switzerland by Metrohm Ltd., CH-9101 Herisau, Switzerland 8.026.5003 – 2003-09

Water Determination by Karl Fischer Titration

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Metrohm Monograph 8.026.50031. Introduction 2. Reagents 3. Chemical reactions 4. Volumetry and coulometry 5. Detection methods (EP) 6. Instruments 7. Side reactions 8. Sample preparation techniques 9. Water determination in raw materials / basic chemicals 10. Water determination in cosmetics and drugs 11. Water determination in foodstuffs and semi-luxuries 12. Water determination in biological samples 13. Waterdetermination in petrochemical products 14. Water determination in plastics 15. Water determination in paints, lacquers, solvents 16. Water determination in gaseous samples 17. Water determination in special samples Appendix
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Literature Index

Water Determination by Karl Fischer Titration

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1. Introduction
In addition to the determination of the pH, weighing and acid-base titration, thedetermination of the water content is one of the most frequently used methods in laboratories around the world. In addition to methods requiring complex apparatus, such as infrared reflection spectrometry, gas chromatography or microwave spectroscopy, two methods in particular have been able to establish themselves: A – Drying methods (drying ovens, infrared lamps and infrared balances). This method iscommonly found in various standards, but suffers from the following disadvantages: – In principle the loss on drying is determined, and not necessarily the water content. Apart from water, other volatile components of the sample and/or decomposition products are also determined. In order to obtain comparable results work must be carried out under strictly maintained predefined conditions(temperature and duration of the drying process). – It takes a long time to obtain the analytical results (several hours in a drying oven). This can lead to bottlenecks, e.g. in the monitoring of manufacturing processes. B –Titration methods In contrast to drying, this is a specific method. If no side reactions occur only water will be determined. The method is rapid (normally a few minutes), can bevalidated and therefore fully documented. Since its introduction more than sixty years ago* its progress has been all-conquering and in many laboratories it is impossible to imagine life without it. The name Karl Fischer (1901–1958), KF for short, is as well known in most laboratories as that of Robert Wilhelm Bunsen (1811 – 1899) and Justus von Liebig (1803 – 1873). With the KF titration both free andbound water can be determined, e.g. surface water on crystals or the water contained inside them. The method works over a wide concentration range from ppm up to 100% and supplies reproducible and correct results.
* Karl Fischer Neues Verfahren zur massanalytischen Bestimmung des Wassergehaltes von Flüssigkeiten und festen Körpern [A new method for the volumetric determination of the watercontent of liquids and solids]

Angew. Chem. 48, (1935) 394 – 396

2. Reagents
When developing his new analytical method Karl Fischer took into account the wellknown Bunsen reaction, which is used for the determination of sulfur dioxide in aqueous solutions: SO2 + I2 + 2 H2O → H2SO4 + 2 HI This reaction can also be used for the determination of water if sulfur dioxide is present in excess and theacids so produced are neutralized by a base. The selection of pyridine, the base used by Karl Fischer, was completely at random: «pyridine was just standing in the rack». This led to the establishment of the classical KF reagent, a solution of iodine and sulfur dioxide in a mixture of pyridine and methanol.
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Original formulation according to Karl Fischer 254 g...