The easiest way to identify PFAS contamination in your LC is to pump mobile phase through the column for 30 minutes to give system-related PFAS a chance to build up at the head of the column. Then, inject a solvent blank, and when the gradient runs through the column, any PFAS that built up on the analytical column will elute and appear at the retention time matching where PFAS in your sample would elute.
Next, inject another solvent blank immediately after the solvent blank injection with the long equilibration time and look at the retention times for PFAS compounds. The purpose of this second injection is to not give enough time for the system-related PFAS to build up in your analytical LC column.
Compare the results of the immediate injection to those of the long equilibration time injection. If there are PFAS peaks in the long equilibration time injection, but not in the injection that immediately followed it, your LC contains system-generated PFAS contaminants that could interfere with trace analysis. If there are not any peaks at the retention times of the PFAS you are looking for in both injections, your instrument may not have a significant amount of system-related PFAS interference. This can occur if you are using an old LC unit with a new mass spectrometry system because most of the leachable, system-related PFAS have already leached out. However, this is not a permanent state; if you replace plastic components in any part of the instrument before the injector, it is highly likely that system-related PFAS interference will leach out unless the new parts are PFAS-free.
