This document provides an overview of Karl-Fischer titration, a method for determining water content in substances. It discusses why water determination is important, how the titration works based on a reaction between iodine and sulfur dioxide, and some key details of the process including the reagents used, sample preparation and collection, and how results are calculated based on the amount of reagent consumed. The document also notes some common applications and advantages/disadvantages of the Karl-Fischer titration technique.
2. CONTENT
1. Why water Determination ?
2. What is Karl Fischer ?
3. Why Karl Fischer Titration ?
4. Working of Karl Fischer Titration.
5. Solvents used for Karl Fischer Titration.
6. Sampling for Karl Fischer Titration.
7. How do we get the result of the sample ?
8. Advantages and disadvantages
3. 1. WHY WATER DETERMINATION ?
• Water content defines the quality and shelf life of the product.
• In pharmaceutical or food products the presence of water helps the
microorganism to grow and due to that the quality of the product may
be compromise.
• To maintain the better quality and shelf life of the substance it is
important to determine the water contain in the substance and make it
possible that the water content must be minimum available or not
available in the substance.
• E.g. We might have seen some medicinal products prescribed by the
Doctor and told us to take by mixing water and the powder (medicine)
at the moment when we are taking it, it is because such products are
unstable in water for the longer time because of that water is added at
the last moment only.
• To prevent the microorganism growth Alcohol is added in most of the
syrup.
4. 2. WHAT IS KARL FISCHER TITRATION ?
• The Karl Fischer Titration is a titration method for measuring the water
content basically in the all types of substances.
• It was Invented in 1935 by the German Chemist Karl Fischer.
• The Karl Fisher titration in based on an Iodine/Iodide reaction; the water
reacts the iodine.
Principle of Karl Fischer Titration
• The principle of Karl Fischer titration is based on the oxidation reaction
between iodine and Sulphur dioxide. Water reacts with iodine and
Sulphur dioxide to form Sulphur trioxide and hydrogen iodide. An
endpoint is reached when all the water is consumed
5. KARL FISCHER TITRATION USED IN..
• Chemical industry
• Pharmaceutical industry
• Petrochemical Industry
• Power stations
• Plastic industry
• Food and beverages
• Paints, Adhesives
• Cosmetic industry and many more…
6. 3. WHY KARL FISCHER TITRATION?
• Selective Determination of water content.
• Drying techniques cannot differentiate between water and moisture.
• Chemically combined water may not be detected completely by loss on
drying method.
• Accurate very small standard deviations are achievable.
• Wide measuring range ppm to %
• Fast 1-3 minutes average per determination.
8. • There is a chamber where we need to add the sample, now we have the dry substance so
we need to dissolve it in methanol.
• We will add the methanol and start initial titration and will ask machine to add iodine
because the methanol has also some water so firstly it will neutralize. So now the
methanol is free from the water.
• So finally methanol is free from water so now we can add the sample in the methanol
• The moment we will add the sample it will get dissolve.
• The moment, the instrument starts it will determine the water content and the H+ ion of
the water or moisture will be attracted with the Karl Fischer reagent, H+ ion will travel
from one electrode to other until this travelling of the H+ ion is continue the instrument
will give signal to add the Karl Fischer reagent and it will be automatically added using
the piston the moment the H+ ion will be finished the bridge will break and we will get
the end point, the addition of the Karl Fischer reagent will be stop.
• The amount of the iodine which is consumed by the sample that is equivalent to water
content.
9. Composition of Karl Fischer Reagent
• I2 (Iodine 45gm) + So2 (Sulphur dioxide 25gm) + C5H5N (pyridine 80gm) + CH3OH (methanol 400ml)
• As the Pyridine is cryogenic in nature, Imidazole C3H4N2 is used instead of it.
Reaction of Karl Fischer titration.
• Step 1 - H2O + SO2 + I2 → SO3 + HI
• Step 2 - SO3 + C5H5N → C5H5N+S02O-
• Step 3 - C5H5N+S02O- + CH3OH → C5H5NHCH3OSO2O-
10. BASIC FORMS OF KARL FISCHER
TITRATION
• Karl Fischer Titration Procedure
• The Karl Fischer titration experiment can be performed in two different
methods. They are:
• Volumetric determination – This technique is suitable to determine
water content down to 1% of water. The sample is dissolved in
KF methanol and the iodine is added to KF Reagent. The endpoint is
detected potentiometrically.
• Coulometric determination – The endpoint is detected in this
experiment electrochemically. Iodine required for KF reaction is obtained
by anodic oxidation of iodide from solution.
11. 5. SOLVENTS USED FOR KF TITRATION
• To determine the water content in a sample, the sample must release
water completely, only freely available water undergoes with the Karl
Fischer reagent
• We can use mixture of the solvents to achieve complete dissolution
• However, the largest part of the solvent mixture must always be an
alcohol i.e. methanol to ensure that the Karl Fischer reaction is strictly
stoichiometric.
• In 99% cases methanol is used as a solvent, in certain case 3 methoxy
ethanol or Dimethylformamide is used if the product contains ketone
group. (As in presence of methanol it forms keto-enol group and it is
needed to be prevented)
• Other Solvents like chloroform, Octanol, Hexanol, Toluene etc. are used
in various fields such as petrochemical, oil, wax products, fatty creams,
sugar products etc..
12. 6. SAMPLING FOR KARL FISCHER
TITRATION
• When taking the samples for water determination, we must be extremely
careful to exclude atmospheric moisture- the most common source of
error.
• If the water content of a sample changes during sampling due to
moisture being absorbed or desorbed, we will no longer be able to
determine its true water content.
• “An analyst cannot be better than the actual sample !!”
13. 1. The sample must be representative, I.e. it must contain the same average amount of
water as the material as a whole.
2. The sample should be taken quickly to exclude, or at least minimize , the absorption or
release of the moisture
3. Heterogeneous water distribution in samples; in non-polar liquids, e.g. oils, the water is
not uniformly dispersed. It floats on the surface or sinks to the bottom. Liquids of this
type must be thoroughly mixed (by shaking) before a sample is taken. In the case of non
polar solids, such as butter, which cannot be mixed thoroughly as liquids, the sample
should be larger the more heterogenous the distribution of the water.
4. Hygroscopic solids may exhibit higher water content on the surface than inside if there
have absorbed atmospheric moisture during storage
5. Substances with very low water content are frequently extremely hygroscopic. The
sample must therefore be taken very quickly and with a syringe or a spatula that is
absolutely dry.
14. 7. HOW DO WE GET THE RESULT ?
• How we start ? We started with the methanol then we neutralize it and
we added sample, now the amount of sample which we have added will
be noted in the system (computer), now it started the procedure so now
the iodine and Sulphur dioxide started reacting with the water at the
moment of end point instrument knows that how much sample was
there for the testing and against it how much reagent get used to
remove the water.
• Instrument knows only the chemistry it doesn’t know the calculation !!
Calculation will be done by the computer.
• Karl Fischer factor. - Approx. 5mg water /1ml Karl fisher reagent
• This factor value varies from 5mg to 6mg, to get this value, reagent
calculation is done before starting the test, for that we will add 5 mg
water we will get the result against KF reagent it may be from 5mg to
6mg
• Based upon such calculation we will get the final result of water content
available in the product.
15. ADVANTAGES DISADVANTAGES
• High accuracy and precision
• Selectively for water
• Short analysis duration
• Easy sample preparation
• Suitability for the analysis of solid,
liquid and gaseous samples
• High cost of apparatus
• Inference of compound reaction with
iodine
• Highly acidic or basic compounds
cannot be determined
• Large amount of sample is needed.
