A direct SPE clean-up after protein precipitation methodology to remove endogenous steroid sulfate MRM interferences...

This paper investigated the feasibility of using direct solid phase extraction (SPE) clean-up after protein precipitation for PFAS analysis of serum samples. Four solid-phase extraction (SPE) cartridge types-EMR-lip (Agilent), ENVI-Carb (Supelco), C18 (Agilent), and ENV+ (ISOLUTE) -were evaluated for their effectiveness in removing endogenous interferences. After protein precipitation with acetonitrile (1% formic acid), ENVI-Carb could remove the multiple reaction monitoring (MRM) isobaric interferences from taurodeoxycholic acid isomers (TDCAs) to perfluorooctanesulfonic acid (PFOS), and the MRM interferences from pregnandiol sulfate and isopregnanalone sulfate to perfluorohexanesulfonic acid (PFHxS). However, perfluorohexadecanoic acid (PFHxDA) could not be analysed after ENVI-Carb cartridge clean-up due to high retention. EMR-lip could only remove TDCAs when the solvent volume is ten times more than the serum sample. The C18 and ENV + cartridges removed less than 50% of TDCAs only. Method detection limits (MDLs) from 0.1 to 0.5 ng mL^-1 were achieved for the majority of PFAS compounds. Acceptable results were achieved for NIST serum Standard Reference Material (SRM) 1957. This preparation method is simple and straightforward and has been successfully applied to PFAS analysis of (PT) serum samples from the Arctic Monitoring and Assessment Programme (AMAP Quebec) and United Nation Environment Programme (UNEP Nairobi).