Stir-bar-sorptive extraction, with in-situ deconjugation, and thermal desorption with in-tube silylation, followed by gas chromatography-mass spectrometry for measurement of urinary 4-nonylphenol and 4-tert-octylphenol glucuronides

Abstract

A novel method, stir-bar-sorptive extraction (SBSE), with in-situ deconjugation and thermal desorption (TD) with in-tube silylation, followed by gas chromatography-mass spectrometry (GC-MS), for determination of trace amounts of 4-nonylphenol glucuronide (NP-G) and 4-tert-octylphenol glucuronide (OP-G) in human urine, is described. The method involved correction by use of stable isotopically labeled internal standards 4-(1-methyl)octylphenol-d5 (NP-d) and deuterium 4-tert-octylphenol (OP-d). A human urine sample to which beta-glucuronidase had been added was extracted for 90 min at 37 degrees C using a stir bar coated with a 500-microm-thick layer of polydimethylsiloxane (PDMS). NP-G and OP-G were deconjugated, becoming free 4-nonylphenol (NP) and 4-tert-octylphenol (OP). The analytes were then extracted with the PDMS stir bar and the stir bar was subjected to TD with in-tube silylation; this was followed by GC-MS in selected-ion-monitoring (SIM) mode. To optimize the conditions for SBSE with in-situ deconjugation and to test recovery, NP-G and OP-G were synthesized by a biochemical technique in our laboratory. Average recoveries from human urine samples spiked with NP-G and OP-G were between 91.9 and 95.6% with correction using the added surrogate standards. Limits of detection were 0.11 ng mL-1 for NP and 0.01 ng mL-1 for OP. We also measured background levels of NP-G and OP-G in six urine samples from healthy volunteers. NP and OP were detected in the samples at concentrations of 0.62-1.95 ng mL-1 and <0.04-0.18 ng mL-1, respectively.