A novel method for the quantitative determination of free and conjugated bisphenol A in human maternal and umbilical cord blood serum using a two-step solid phase extraction and gas chromatography/tandem mass spectrometry
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Bisphenol A is widely used as a monomer in the manufacture of polycarbonates and epoxy resins, as an antioxidant in polyvinyl chloride (PVC) plastics and as an inhibitor of end polymerisation in PVC. Several different methods have been used to quantify total BPA in biological specimens. However, quantification of both free and conjugated BPA continues to present challenges. Moreover, there is limited data concerning fetal exposure. Therefore, the objective of this study was to develop a new method for the analysis of both free and conjugated BPA in human maternal and umbilical cord blood serum. For the analysis of free BPA, the method consisted of a liquid-liquid extraction followed by a two-step solid-phase extraction sample cleanup on Florisil and Oasis HLB sorbents, derivatization of the extract using N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) and analysis by gas chromatography/tandem mass spectrometry (GC/EI-MS/MS). To determine the amount of conjugated BPA in serum samples, bisphenol A-d6 β-glucuronide (4-[1-(4-hydroxyphenyl)-1-methylethyl-d6]phenyl β-D-glucopyranosiduronic acid) was added to each sample prior to enzymatic deconjugation. The MDL and LOQ for BPA were 0.026 ng/mL and 0.087 ng/mL, respectively. The observed recoveries ranged between 65% and 88%. The new method was applied to the determination of paired human maternal and umbilical cord blood serum samples. The results demonstrated that total BPA concentrations in human maternal serum at mid-pregnancy and at delivery ranged from <0.026 ng/mL to 10.425 ng/mL (median 0.548 ng/mL, n=12) and <0.026 ng/mL to 3.048 ng/mL (median 1.461 ng/mL), respectively. Results for matching umbilical cord blood serum BPA concentrations were in the range of <0.026-2.569 ng/mL (median 1.823 ng/mL). The concentrations measured in this study agreed well with BPA levels in human serum reported internationally. Only 2 mid-pregnancy serum samples out of 12 contained quantifiable amounts of conjugated BPA, indicating that BPA-glucuronide is not abundant in either human maternal or umbilical cord blood serum.
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