Microwave-accelerated derivatization for the simultaneous gas chromatographic–mass spectrometric analysis of natural and synthetic estrogenic steroids

A rapid microwave-accelerated derivatization process for the GC–MS analysis of steroid estrogens, estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethynylestradiol (EE2) and mestranol (MeEE2), was developed. Under microwave irradiation, the five estrogenic hormones studied were simultaneously derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) + trimethylchlorosilane (TMCS) in pyridine solution. Effects of irradiation time (15–120 s) and power level (240–800 W) on the yield of the derivatization were investigated. The derivatization under the irradiation of 800 W microwave for 60 s produced comparable results when compared with the conventional heating process in a sand bath for 30 min at 80 °C in terms of derivatization yield, linearity and precision for all steroid hormones tested. The calibration curves are linear between 3.00 and 3.00 × 102 μg mL−1. The square of the regression coefficients (R2) range from 0.979 to 1.000. The applicability of the method was evaluated on spiked river and distilled water samples at two concentrations, 25.0 and 2.00 × 102 ng mL−1. The recoveries obtained by using microwave heating (60 s, 800 W) were similar to those by conventional heating. When combined solid-phase extraction (SPE) with the application of the microwave-accelerated derivatization proposed here, the detection limits of 0.02–0.1 ng L−1 for the steroid hormones have been achieved. The results demonstrated that microwave-accelerated derivatization is an efficient and suitable sample preparation method for the GC–MS analysis of estrogenic steroids.