karl fischer titration

[swapna]

can anybody explain how is the factor calculated and how is percentage of water content present in the sample(specifically in drug powder) calculated when we do the standardisation with purified water.

[chromatographer1]

the reagent in the titrator must be calibrated to determine how much water per volume of titrant will be reacted.

Usually a standard with a known amount of water is weighed out for titration. This std is titrated with the reagent and the 'strength' or volume of titrant needed to react with water is calculated. The titrant is then used to titrate an exact weight of an unknown. The volume of titrant needed to react is then measured and the amount of water that reacted with the titrant is calculated. This water is then determined as a weight percent of the weight of the unknown.

[mass]

Hi swapna,

It is simple volumatric titration u can calculate the factor using either by water or by disodiumtartrate. If you chosed water then you will take the weight of water and volume of kf reagent consumed. KF reagent consumed equal to the 100% water of weight u have taken, from that u will get for one millilter of KF reagent equals to some amount of water it is the factor.

Factor = 100(% of water) X weight taken (water g )/ Volume consumed(KF) X 100

Then it will help you to find out the unkown compounds moisture content.
Hope u will understood this concept.

Unknown water content = factor X Volume consumed(KF)/weight in g X 100

Feel free to ask me if you have any further doubts regarding this.

Bye
massnmass@yahoo.com

[swapna]

hello mass,
100%water means what value will to substitute there. i think u got the wrong equation. the correct equation is
factor=weight in of water in mg/volume of kf reagent in ml


and the unknown water content u dont multiply with 100 but multiplied with 0.1
unknown water=factor X volume consumed(kf) X0.1/weight in gm


i would like to know how the electrode in kf tirator works?
please help

[mass]

swapna,

If you hav taken water the equation u have given is correct, ok (mine is also correct), But if you have taken disodium tartrate then?

think of it ,just you have made Both Hundreds gets cancelled. I have given generalised equation.

[mass]

swapna,

Regarding platinum electrode in KF titrator. The electrode system consists of an anode and cathode platinum electrodes which conducts current through the cell, generates iodine at the anode, which then subsequently reacts with the water in the sample.
The platinum indicating electrode determines when and if iodine generation is necessary to react with any moisture in the sample.
It does this by voltametrically sensing the presence of water and then continues to generate iodine until all the water in the sample has been reacted with - the KF end-point.
From this titration the on board microprocessor in the instrument calculates the total amount of current consumed in completing the titration and the time to completion in seconds.
Based on the relationship between coulombs and iodine the exact amount of iodine generated is determined.
Since water reacts in the 1:1 ratio with iodine, the amount of water can be calculated.