Measurement of ethynylestradiol and levonorgestrel incorporated into sustained release contraceptive formulations.

ABSTRACT

PIP: High performance liquid chromatography was used to measure the concentrations of ethinyl estradiol (EE) and levonorgestrel (LNG) released from contraceptive devices into aqueous medium containing the cationic detergent, benzalkonium chloride. Most of the detergent was removed after solvent extraction of the steroid, although small amounts of it remained in the steroid phase. Over the course of many injections into octasilyl (CB) or octadecylsilyl (C18) reversed-phase columns, the chromatographic profile of EE was gradually altered with multiple peaks emerging. The profile of LNG was not changed. EE chromatographed as a double peak on a fully end-capped C18 column. Rechromatography of each peak yielded a mixture of the 2. Mass spectral analysis showed that the peaks differed only in the gain or loss of an equivalent of water. Introduction of a cation exchange column before the analytical column removed residual benzalkonium ions, and by thus preventing deterioration of the column, permitted EE to consistently emerge as a single, symmetrical peak. The author asserts in this paper that it is important to remove trace amounts of cationic surfactant such as benzalkonum chloride before injecting anionic compounds like EE repeatedly into reverse phase columns. It is likely that other ionic detergents may also have an adverse effect on column life and distort the emerging chromatographic patterns of charged molecules. The procedure described in this paper provides a way to overcome these problems in laboratory procedural analyses.