Method EPA 537 is testing used for the analysis of perfluorinated alkyl acids (PFAS). Six analytes are detected and quantified by this method:
- perfluorooctanesulfonic acid (PFOS)
- perfluorooctanoic acid (PFOA)
- perfluorononanoic acid (PFNA)
- perfluorohexanesulfonic acid (PFHxS)
- perfluoroheptanoic acid (PFHpA)
- perfluorobutanesulfonic acid (PFBS)
The first step in the process is to fortify the sample with surrogates and pass it through a solid phase extraction (SPE) cartridge containing polystyrenedivinylbenzene (SDVB). This allows for extraction of the method analytes and the surrogates. Next, the compounds are eluted from the solid phase with a small amount of methanol. After this, the sample is then concentrated to dryness with nitrogen in a heated water bath. They are then adjusted to a 1-mL volume with 96:4% (vol/vol) methanol:water after adding the internal standards.
The extracts are then injected into liquid chromatograph where the analytes are separated based on polarity. After this, they are passed into two mass spectrometer in tandem for identification based on the molecular masses of the fragmented compounds. This analysis provides a high precise quantitation of these compounds.