LC-MS/MS analysis is a very sensitive, selective technique that is used in many different applications and is ideally suited for multi-analyte analysis. Due to their chemical/physical properties and long-lasting inertness, plastic fluoropolymers, such as polytetrafluoroethylene (PTFE), are used to make many LC-MS/MS components. You can find PTFE in LC pump seals, mobile phase transfer lines, the plastic linings used in degassers, etc. Unfortunately, these plastic parts can leach PFAS into the mobile phase, which creates system-related background PFAS contamination that interferes with trace-level PFAS analysis. Because PFAS detection levels in drinking water are in ppt range, even slight interference can bias quantitative analysis.
PFAS interference can also come from the solvents (even new bottles) used to make mobile phase due to the ubiquitous use of PFAS compounds. PFAS are found in the air as well, so you can assume PFAS contaminants are literally everywhere at low concentration. Basically, system-related PFAS come from components in all stages of the LC-MS/MS workflow, including the sample collection bottle; mobile phase cap/lining (made of PTFE); solvent inlet tubing (often FEP or PFA); degasser; LC pump parts; and even the autosampler vial septum (many are PTFE-lined silicone).
The degree of interference that is observed will vary across LC instrument manufacturers and also depends on method parameters (e.g., equilibration time, solvent choice, target analytes, etc.) Note that the longer equilibration times produce more interference because PFAS have more time to leach out of the plastic parts.
