Suspect screening of maternal serum to identify new environmental chemical biomonitoring targets using liquid chromatography-quadrupole time-of-flight mass spectrometry

Abstract

The use and advantages of high-resolution mass spectrometry (MS) as a discovery tool for environmental chemical monitoring has been demonstrated for environmental samples but not for biological samples. We developed a method using liquid chromatography-quadrupole time-of-flight MS (LC-QTOF/MS) for discovery of previously unmeasured environmental chemicals in human serum. Using non-targeted data acquisition (full scan MS analysis) we were able to screen for environmental organic acids (EOAs) in 20 serum samples from second trimester pregnant women. We define EOAs as environmental organic compounds with at least one dissociable proton which are utilized in commerce. EOAs include environmental phenols, phthalate metabolites, perfluorinated compounds, phenolic metabolites of polybrominated diphenyl ethers and polychlorinated biphenyls, and acidic pesticides and/or predicted acidic pesticide metabolites. Our validated method used solid phase extraction, reversed-phase chromatography in a C18 column with gradient elution, electrospray ionization in negative polarity and automated tandem MS (MS/MS) data acquisition to maximize true positive rates. We identified "suspect EOAs" using Agilent MassHunter Qualitative Analysis software, to match chemical formulas generated from each sample run with molecular formulas in our unique database of 693 EOAs assembled from multiple environmental literature sources. We found potential matches for 282 (41%) of the EOAs in our database. Sixty-five of these suspect EOAs were detected in at least 75% of the samples; only 19 of these compounds are currently biomonitored in National Health and Nutrition Examination Survey. We confirmed two of three suspect EOAs by LC-QTOF/MS using a targeted method developed through LC-MS/MS, reporting the first confirmation of benzophenone-1 and bisphenol S in pregnant women's sera. Our suspect screening workflow provides an approach to comprehensively scan environmental chemical exposures in humans. This can provide a better source of exposure information to help improve exposure and risk evaluation of industrial chemicals.

Figure 1.

Overview of General Suspect Screening Data Inputs and Workflow to identify suspect Environmental Organic Acids in pregnant women serum. ¹ Total Ion Chromatogram contains accurate mass, retention time, and peak areas of all precursor and product ions detected in each serum sample ² Criteria for accurate mass match: 1) Formula mass match ±10 ppm error; 2) Peak area >500 arbitrary units; 3) Signal-to-noise ratio ≥ 3; 4) Target score (accurate mass and isotopic pattern) ≥ 70. ³ Criteria for Retention Time Plausibility: 1) ± 0.5 min, accounting for RT drift; 2) consistent with chemical structure and predicted polarity.

Figure 2.

Number of non-isomer and isomer EOAs and number of isomers per molecular formula for the 176 isomers in the EOA Database (n= 693 EOAs).

Figure 3.

Number of suspect EOAs, by compound class, in 20 maternal serum samples

Figure 4.

Typical chromatogram obtained for the targeted analysis of bisphenol S, benzophenone-1 and monopentyl phthalate using liquid chromatography-tandem mass spectrometry (LC-MS/MS)