An isotope dilution gas chromatographic-mass spectrometric method for the simultaneous assay of estrogens and phytoestrogens in urine

The metabolism of endogenous estrogens is complicated and certain metabolic patterns may reflect an individual risk of estrogen-dependent diseases such as breast cancer. Since the 1960s we have been constantly involved in developing estrogen profiling methods, in the beginning using gas chromatography and later gas chromatography–mass spectrometry (GC–MS) in the selected ion monitoring mode (SIM) and finally utilizing isotope dilution (ID–GC–MS–SIM). The addition of the dietary phytoestrogens to the profile rendered the method even more complicated. The present work presents the final estrogen profile method for 15 endogenous estrogens, four lignans, seven isoflavonoids and coumestrol in one small urine sample (1/150th of a 24 h human urine sample, minimum 2.5–5 ml) with complete validation including investigations as to the precision, sensitivity, accuracy and specificity. The method does not include the minimal amounts of unconjugated estrogens in urine. It may also be used for animal (e.g. rat and mouse) urine using a minimum of 2 ml of usually pooled sample. Despite its complexity it was found to fulfill the reliability criteria, resulting in highly specific and accurate results.