A high-throughput small volume matrix based calibration using isotope dilution liquid chromatography tandem mass spectrometry analysis for 42 per and polyfluoroalkyl substances in groundwater.

A novel method for the determination of per- and polyfluoroalkyl substances (PFAS) in groundwater is presented using a subsample, matrix-matched calibrators, 96-well plate solid phase extraction (SPE), and ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). Accuracy, precision, measurement of uncertainty (MOU), method detection limit (MDL), method quantitation limit (MQL), analytical measurement range, interferences/ion suppression, and analyte stability were determined as part of the in-house method validation. The method quantitates 42 PFAS compounds from nine different compound classes. Accuracy for the reference material (RM) and matrix spike (MS) ranged from 52.3 to 117.8 %, and precision for the MS and matrix spike duplicate (MSD) had a coefficient of variation (CV) from 2.0 % to 23.3 %. MDLs spanned from 0.07 to 1.97 ng L-1, with MQLs ranging from 0.20 to 5.90 ng L-1. Suppression studies determined that iron and manganese have effects on analytes that do not have paired isotopically labeled standards. The results from the in-house validation indicated that this Michigan Department of Health and Human Services laboratory developed test meets the necessary accuracy, precision, MDL, MQL and reporting limits requirement established by the laboratory's quality system essentials (QSEs) and select criteria from the Department of Defense (DoD) Quality Systems Manual for Environmental Laboratories and American Industrial Hygiene Association Laboratory Accreditation Program, LLC (AIHA LAP, LLC) accrediting International Standard Organization (ISO/IEC 17025:2017) check list.

Bioassay-directed fractionation for discovery of bioactive neutral lipids guided by relative mass defect filtering and multiplexed collision-induced dissociation.

We report a synergistic method using bioassay-directed liquid chromatography fractionation and time-of-flight mass spectrometry to guide and accelerate bioactive compound discovery. To steer purification and assays toward anticipated neutral lipid activators of a constitutive androstane receptor splice variant, a relative mass defect filter was calculated, based on the ratio of the mass defect to the measured ion mass, and used to reduce the number of candidate ion masses. Mass measurements often lack sufficient accuracy to provide unambiguous assignments of elemental compositions, and since the relative mass defect reflects fractional hydrogen content of ions, this value is largely determined by the hydrogen content of a compound's biosynthetic precursors. A relative mass defect window ranging from 600-1000 ppm, consistent with an assortment of lipids, was chosen to assess the number of candidate ions in fractions of fetal bovine serum. This filter reduced the number of candidate ion m/z values from 1345 to 892, which was further reduced to 21 by intensity and isotope filtering. Accurate mass measurements from time-of-flight mass spectrometry and fragment ion masses generated using nonselective collision-induced dissociation suggested dioctyl phthalate as one of few neutral lipid constituents in the active fraction. The identity of this compound was determined to be di(2-ethylhexyl) phthalate using GC/MS, and it was ranked as a promising candidate for reporter assay screening.

Di(2-ethylhexyl) phthalate is a highly potent agonist for the human constitutive androstane receptor splice variant CAR2.

The human constitutive androstane receptor (CAR, CAR1) regulates the expression of genes involved in xenobiotic metabolism in the liver. The CAR gene uses multiple alternative splicing events during pre-mRNA processing, thereby enhancing the CAR transcriptome. Previous reports have identified two prominent human CAR variants, CAR2 and CAR3, that possess four- and five-amino acid insertions in their ligand binding domains, respectively. Unlike the constitutively active reference form of the receptor, we now demonstrate that CAR2 is a ligand-activated receptor and comprises approximately 30% of the reference transcript level in human liver tissues in human hepatocytes. Furthermore, we identify the common plasticizer, di(2-ethylhexyl) phthalate (DEHP), as a highly potent and uniquely selective agonist of CAR2. Results from reporter transactivation and mammalian two-hybrid assays reveal that DEHP activates CAR2 at low nanomolar concentrations, results further supported by analysis of CAR target gene expression in primary human hepatocytes. In addition, comparative genomic analyses show that the typical mouse, rat, and marmoset models of DEHP toxicity cannot accurately profile potential human toxicity because of these species' inability to generate a CAR2-like transcript. The discovery that CAR2 is an ultimate human DEHP receptor identifies a novel pathway modulating human DEHP toxicity with potential clinical implications for a subset of patients undergoing critical care medical interventions.