A new silylation reagent dimethyl(3,3,3-trifluoropropyl)silyldiethylamine for the analysis of estrogenic compounds by gas chromatography-mass spectrometry

Abstract

In this study we applied DIMETRIS (dimethyl(3,3,3-trifluoropropyl)silyldiethylamine), a new silylating reagent, to derivative natural estrogens such as estrone (E1), 17β-estradiol (E2) and estriol (E3), as well as the synthetic 17α-ethinylestradiol (EE2) and the non-steroid diethylstilbestrol (DES). Its derivatizing properties were compared with those of the commonly used mixture of BSTFA (N,O-bis(trimethylsilyl)trifluoroacetamide)+1% trimethylchlorosilane (TMCS) and with MTBSTFA (N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide). The use of DIMETRIS for the silylation all of them is reported for the first time. The nucleophilic properties of DIMETRIS were found to be superior to those of MTBSTFA, but slightly inferior to those of BSTFA. It was used to derivatize steroid (E1, E2, E3 and EE2) and non-steroid (DES) estrogens at 30°C prior to GC/MS analysis. These DMTFPS-derivatives exhibited good separation (low retention times despite the high molecular masses) and ionization properties in GC/MS analyses (the highest relative response factors for DMTFPS-derivatives among those tested). However, DIMETRIS and MTBSTFA (which produce mono-O-silyl derivatives of EE2) should not be used for the simultaneous analysis of EE2 and E1. Only a mixture of BSTFA+1% TMCS in pyridine, which generates the fully derivatized EE2 product (stable in GC injector), permits the determination of these two estrogenic compounds during one GC-MS run. On the other hand, because DIMETRIS requires a lower derivatization temperature than BSTFA, it could be very useful for the derivatization of thermally unstable estrogenic compounds. In the next step of this study, the SPE-GC-MS method based on DIMETRIS derivatization for the analysis of DES, E2 and E3 in aqueous samples was evaluated and validated. The MQL values: 1.4, 1.6 and 1.5ngL(-1) for DES, E2 and E3, respectively, proved its suitability to determine target compounds in environmental samples. Finally, the proposed method was successfully applied to the analysis of selected estrogenic compounds in real seawater and wastewater samples in Poland.

Keywords: Comparative study; DIMETRIS; Estrogenic compounds; Fragmentation pattern; Mass spectra analysis; Silylation.