Formation of multiple trimethylsilyl derivatives in the derivatization of 17alpha-ethinylestradiol with BSTFA or MSTFA followed by gas chromatography-mass spectrometry determination.
ABSTRACT N,O-bis(trimethylsily)trifluoroacetamide (BSTFA) and N-methyl-N(trimethylsily) trifluoroacetamide (MSTFA) are common derivatization reagents used in the GC-MS analysis of estrogen steroids such as estrone (El) and 17alpha-ethinylestradiol (EE2). In this study, three trimethylsilyl (TMS) steroid derivatives, mono- and di-trimethylsilyl EE2 and mono-trimethylsilyl E1, were observed during the derivatization of EE2 with BSTFA or MSTFA and/or GC separation. Factors influencing the production of multiple TMS derivatives and their relative abundance were examined. It was found that both methanol and bisphenol A competed with estrogenic esteroids when reacting with silylation reagents, and thus affected the formation of TMS derivatives and their relative abundance in the derivatization products. Methanol was found to be more reactive than bisphenol A with the BSTFA reagent. None of the three solvents tested in this study could prevent the generation of multiple TMS derivatives during the derivatization of EE2 with BSTFA, followed by GC analysis. A similar result was observed using MSTFA as the derivative reagent followed by GC analysis. Thus, the suitability of BSTFA or MSTFA as the derivatization reagent for the determination of E1 and EE2 by GC-MS, under the conditions reported here, is questionable. This problem can be solved by adding trimethylsilylimidaz (TMSI) in the BSTFA reagent as recommended, and the performance of the method has been proved in this study.
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ABSTRACT: Neutral pentacyclic triterpenes with only one or two hydroxyl groups, such as betulin, are not easily ionized by electrospray ionization (ESI). However, because betulin is reactive and neutral, derivatization may improve ionization efficiency. In the present study, the potency of different derivatization reagents was evaluated and p-toluenesulfonyl isocyanate (PTSI) was proven to be the optimal. The derivative generated by the reaction of betulin with PTSI was ionizable and fragmentable in the negative mode by liquid chromatography-electrospray ionization/tandem mass spectrometry (LC-ESI/MS/MS). Based on this chemical derivatization, an LC-ESI/MS/MS method was developed and validated for the quantification of betulin in rat plasma. The sample was extracted with ethyl acetate, derivatized with PTSI, separated on an ACQ UPLC BEH phenyl column, and analyzed in negative multiple reaction monitoring (MRM) mode. The calibration curve was linear over the betulin concentration range 2.5-200ng/mL. The lower limit of quantification was 2.5ng/mL. The inter- and intra-day accuracy and precision were within ±15%. Betulin recoveries were 86.7% or higher at three quality control levels (5, 50, and 160ng/mL). This validated method was subsequently applied to a pharmacokinetic study of betulin in rat plasma after oral administration.Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 09/2013; 939C:38-44. · 2.78 Impact Factor
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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.Journal of Chromatography A 06/2013; · 4.61 Impact Factor
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ABSTRACT: Metabolomics is currently being adopted as a tool to understand numerous clinical pathologies. It is essential to choose the best combination of techniques in order to optimize the information gained from the biological sample examined. For example, separation by reverse-phase liquid chromatography may be suitable for biological fluids in which lipids, proteins and small organic compounds coexist in a relatively nonpolar environment, such as serum. However, urine is a highly polar environment and metabolites are often specifically altered to render them polar suitable for normal phase/hydrophilic interaction liquid chromatography. Similarly, detectors such as high-resolution mass spectrometry (MS) may negate the need for a pre-separation but specific detection and quantification of less abundant analytes in targeted metabolomics may require concentration of the ions by methods such an ion trap MS. In addition, the inherent variability of metabolomic profiles need to be established in appropriately large sample sets of normal controls. This review aims to explore various techniques that have been tried and tested over the past decade. Consideration is given to various key drawbacks and positive alternatives published by active research groups and an optimum combination that should be used for urinary metabolomics is suggested to generate a reliable dataset for baseline studies. Copyright © 2014 John Wiley & Sons, Ltd.Biomedical Chromatography 04/2014; · 1.95 Impact Factor