Analysis of steroids. Part XXVII. Difference spectrophotometric determination of oestrogens in oily injections in the presence of 4-ene-3-ketosteroids

Abstract

A difference spectrophotometric method is described for the determination of 2.5–5 mg ml^–1 amounts of oestrogens (esters of oestrone and oestradiol) in oily injections in the presence of a large excess of 4-ene-3-ketosteroids. The method is based on a bathochromic shift of the ultraviolet spectrum of the extracts of the samples in methanol in alkaline media. Any interference caused by co-extracted oil or by unsaturated ketosteroids is eliminated by careful choice of pH settings (9.2 for the reference solution by using borate buffer and the test solution 0.2 N in sodium hydroxide) and reduction with sodium borohydride, respectively. The difference between the results found and the label claims for four formulations was less than 2% and the relative standard deviations ranged between 1.1 and 1.7%.