[michaelcar]

Hi All


We are busy testing Glutathione as per BP monograph. I would like to confirm the calculation for the assay as there is no calculation in the monograph.

BP Assay method: 
In a ground-glass-stoppered flask, dissolve 0.500 g of the substance to be examined and 2 g of potassium iodide R in 50 mL of water R. Cool the solution in iced water and add 10 mL of hydrochloric acid R1 and 20.0 mL of 0.05 M iodine. Stopper the flask and allow to stand in the dark for 15 min. Titrate with 0.1 M sodium thiosulfate using 1 mL of starch solution R, added towards the end of the titration, as indicator. Carry out a blank titration.

1 mL of 0.05 M iodine is equivalent to 30.73 mg of C10H17N3O6S

Is the calculation for the Assay as follows:

% = (Blank - Titre) x F x 30.73 X 100 x 100
        mass of sample (mg) x (100 - % LOD)

Where,

Blank = Volume of titrant of the blank (mL)
Titre = Volume of titrant of the sample (mL)
F = factor of the 0.05 M Iodine
30.73 = equivalence factor
mass of sample = mass of sample weighed off (mg)
%LOD = % Loss on drying

Thanks so much for the assistance.

Mike

[AWK]

Your formula looks OK. For pure GSH The Blank will be 20 and the Titre about 5.
I'm worried about the GSH drying method, which is easily oxidized with air oxygen at elevated temperatures.