A stable and sensitive colorimetric method for the determination of ergocalciferol (vitamin D2) by using trifluoroacetic acid

Abstract

A sensitive and fairly stable colour for the spectrophotometric determination of ergocalciferol (vitamin D₂) following reaction with trifluoroacetic acid has been developed. In the method hydroquinone was used to stabilise the yellow colour, which reached maximum absorbance in not less than 80 s and remained stable for at least 20 s, thus giving the analyst convenient time to carry out the determination. Maximum absorbance was reached at a wavelength of 490 nm. The colour could be destroyed within 2 minutes by the addition of hydrogen peroxide solution, which property was used to advantage in differential spectroscopy. The absorbance is linear for ergocalciferol solutions containing from 0 to 32 µg, optimum results being obtained in the 5 to 15-µg range. The relative standard deviation of the method is ±1·76 per cent.