Serum samples from both cohorts are centrifuged and aliquoted prior to storage at −80 °C at cohort sites and later stored at −20 °C at the Environmental Chemical Laboratory at the California Department of Toxic Substances Control (DTSC), which quantified 12 PFAS in both cohorts (perfluoro butane sulfonate (PFBS), perfluorohexanesulphonic acid (PFHxS), perflucorooctane sulfonic acid (PFOS), perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDeA), perfluoroundecanoic acid (PFUdA), perfluorododecanoic acid (PFDoA), perfluorooctane sulfonamide (PFOSA), methyl-perfluorooctane sulfonamide acetic acid (Me-PFOSA-AcOH), ethyl-perfluorooctane sulfonamide acetic acid (Et-PFOSA-AcOH)). The samples are extracted and analyzed using a Symbiosis Pharma automated online solid-phase extraction system (Spark Holland) coupled with liquid chromatography and tandem mass spectrometry to quantify PFAS. The method detection limit (MDL) is calculated as 3 times the standard deviation of the blank concentrations for all PFAS [33 (link)]. Values below the MDL are assigned the machine read value if a signal is detected. Those below the MDL where no signal is obtained are coded as missing. Additional information regarding PFAS measurement is provided elsewhere [33 (link),34 (link)].
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