SOME OBSERVATIONS ON THE SULPHURIC ACID COLOUR REACTION FOR THE ESTIMATION OF PREGNANEDIOL

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Abstract
SUMMARY When a solution of pregnanediol in concentrated sulphuric acid is heated at 25° C for 17 hr, the spectrum of the colour complex formed is different from the spectrum of pregnanediol diacetate similarly treated. The intensity of colour of such solutions increases rapidly for 8 hr. Thereafter the rate of increase slows down; maximum colour development is reached in 17–20 hr. At temperatures above 25° C the characteristic light absorption pattern of the steroid-acid solution becomes progressively obliterated. The intensity of colour is decreased by hydrogen peroxide and by barium nitrate; it is increased by sodium sulphite and hydroquinone. The same weight of pregnanediol may give different spectrophotometric readings if different stock samples of sulphuric acid are used. These differences may be greatly reduced by pretreating the sulphuric acid with sodium sulphite.

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