How It Works: The Karl Fischer Titration

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How It Works: The Karl Fischer Titration

History of Karl Fischer Titration •Karl Fischer (March 24, 1901 – April 16, 1958) was a German chemist •Published a method in 1935 to determine trace

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How It Works: The Karl Fischer

Titration

Anthony Lucio

The University of Iowa

Shaw Group Meeting

3/7/2013

History of Karl Fischer Titration

Karl Fischer (March 24, 1901 - April 16, 1958) was a German chemist

Published a method in 1935 to determine trace amounts of water in samples. This method is now called Karl Fischer titration. Abbreviations: KF or KFT

It remains the primary method of water content determination used worldwide by:

Government - Food Science

Academia - Research

Industry - Quality Control

Karl Fischer Reaction

Bunsen Reaction:

2H2O + SO2 + I2 AE H2SO4 + 2HI

ROH + SO2 н R'N AE ΀R'NH΁SO3R + H2O + I2 н 2R'N AE 2΀R'NH΁I н ΀R'NH΁SO4R Once the intermediate alkylsulfite salt is produced, it is oxidized by iodine to the alkylsulfate salt

Oxidation reaction consumes water

pH sensitive: optimal range pH 5 - 8 otherwise buffer highly acidic/basic samples 3 alcohol base alkylsulfite salt alkylsulfate salt hydroiodic acid salt

Cartoon Karl Fischer Cell

Water and iodine are consumed

in a 1:1 mole ratio in the KF reaction

Once the reaction consumes all

of the water present, the presence of excess iodine is detected by the indicator electrode

Percent water is calculated based

on the [I2] in the Karl Fischer titrating reagent (i.e. titer) an the amount of KF reagent consumed

Two Types of Karl Fischer Titration

Volumetric

Iodine is added mechanically to a solvent containing the sample

Water is quantified from the volume of KF reagent

consumed

100 to 1x106 ppm (0.01 - 100%)

Coulometric

Iodine is generated electrochemically in situ during the titration

Water is quantified from the total charged passed

Q = 1 C = 1 A x 1 s where 1 mg H2O = 10.72 C

1 to 50,000 ppm (0.0001 - 5%)

General Sample Size Requirements

Metrohm 716 DMS Titrino

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