COLORIMETRIC ESTIMATION OF DIGITALIS GLYCOSIDES WITH 2:4-DINITRODIPHENYLSULPHONE

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Abstract
The reaction is carried out as follows. The glycoside or aglycone, dissolved in 4ml. of ethanol, is mixed with 5 ml. of a 0ṁ075 per cent solution of 2:4-dinitrodiphenylsulphone in ethanol followed by 1 ml. of 0ṁ15N sodium hydroxide. Colour density is measured in a 0ṁ5 cm. cell at 20° at a wavelength of 6,000 Å against a blank prepared as the reaction mixture but omitting the glycoside or aglycone. Maximum extinction values of digitoxigenin and of gitoxigenin, boiled with 0ṁ4N acid, are obtained 3 minutes after adding the sodium hydroxide to the reaction mixture. When digitoxin or digitoxigenin are examined without any pre-treatment with boiling acid, maximum colour is obtained 5ṁ5 and 4ṁ5 minutes respectively after addition of the alkali. Molar extinctions of digitoxin and of digitoxigenin are 23,200 and 24,400 respectively: after boiling with 0ṁ4N acid the molar extinctions of digitoxigenin and gitoxigenin are 29,100 and 18,100 respectively. The values are much higher than those obtained with other reagents. A reduction in the ethanol concentration of the reaction mixture only exerts a slight influence on the maximum extinction.