Chromatographic Techniques for Improving the LC/MS Quantification of PFAS

The liquid chromatography / mass spectrometry (LC/MS) quantification of per- and polyfluoroalkyl substances (PFAS) in complex matrices presents challenges. Despite advanced sample preparation techniques to isolate analytes, residual matrix components can still interfere with MS detection. Additionally, extracts often contain high levels of organic solvents limiting the volume that can be injected when using reversed-phase HPLC. Yet, increasing the injection volume could be a simple path to lower detection limits. Feeding PFAS samples, dissolved in pure acetonitrile, at controlled speed into the stream of mobile phase resulted in an analyte focusing effect on the column. By using this approach, the injection volume could be increased 10 times compared to the conventional injection mode, as did the detection sensitivity. Feed injection was coupled to two-dimensional liquid chromatography (2D-LC) in a configuration in which the same triple quadrupole MS could be used for detection in both separation dimensions. The improved separation markedly reduced ion suppression effects and allowed to distinguish the critical PFAS compound perfluorobutanoic acid (PFBA) from isomeric matrix components within tomato extracts interfering with its quantification when only LC/MS was used. This 2D-LC/MS approach therefore fulfilled recommendations that PFBA should be analyzed using a secondary LC approach, without adding a marked amount of time to the analysis.