Multiresponse optimization and parallel factor analysis, useful tools in the determination of estrogens by gas chromatography-mass spectrometry

This paper reports an experimental design optimization of a recently proposed silylation procedure that avoids the introduction of false positives and false negatives in the simultaneous determination of steroid hormone estrone (E1) and 17-alpha-ethinylestradiol (EE2) by gas chromatography-mass spectrometry (GC/MS). The figures of merit for several calibration procedures were evaluated under optimum conditions in the silylation step. Internal standardization strategies were applied and global models were constructed by gathering signals recorded on three non-consecutive days. Three calibration models were examined: a univariate model with a sum of six monitorized ions and a three-way PARAFAC-based model (the analyte scores were standardized on the basis of the scores of the internal standard). The global PARAFAC-based calibration model showed the best performance with detection capabilities of 4.3 microg l(-1) and 7.0 microg l(-1) for E1 and EE2, respectively, when the probability of false positives was fixed at 1% and that of false negatives at 5%. Mean relative error in absolute terms for E1 and for EE2 was 11.1% and 8.5%, respectively, and trueness was likewise confirmed. The proposed optimized derivatization procedure using a three-way calibration function was also applied in the determination of E1, 17-beta-estradiol (E2) and EE2 in bovine urine samples: recovery values were 68.5%, 40.4% and 43.4%, respectively, and the detection capability was 18.4, 19.3 and 18.6 microg l(-1) when the probability of false positives was fixed at 1% and that of false negatives at 5%. Mean relative error in absolute terms for E1, E2 and EE2 was 7.4%, 9.4% and 8.6%, respectively, and trueness was likewise confirmed.