Column Chemistry Considerations Affecting PFAS Selectivity for LC-MS/MS Workflows

Polyfluoroalkyl Substances (PFAS) in the Environment
Poster Presentation

Prepared by R. Jack, S. Lodge, Z. Jalali
Phenomenex, 86 Lester ave, San Jose, CA, 95125, United States


Contact Information: [email protected]; 408-242-2996

ABSTRACT

LC-MS/MS workflows for PFAS analysis in environment drinking water and solid waste samples cover a wide range of sample preparations, target analytes and analyte ranges. As the required analytes continue to increase in number - including PFAS replacement compounds (GenX) and short-chained PFAS - laboratories running strategies of overlapping PFAS compounds, with poor resolution are often overlooked. The chromatographic separation of PFAS compounds in currently validated methods typically involves a reversed phase mechanism using a C18 or Phenyl column in an acidic-methanol eluent. For example, EPA method 537.1 uses a C18 column (5 µm, 2.1 x 150 mm C18) and EPA Method 533 was validated using a C18 Phenomenex Gemini® column (3 µm, 2 x 50 mm). Conversely, ASTM D7979 and EPA 8327 were validated using a Phenyl-Hexyl column (1.7 µm, 2.1 × 100 mm), ISO 21675 used a C18 column (5 μm, 2 × 50 mm) and the Department of Agriculture CLG-PFAS 2.01 method used a C8 column, Phenomenex Luna® C8(2) (3 µm, 2 x 50 mm). Whereas many of these overlapping peaks can be successfully resolved by the mass analyzer, the potential presence of isobaric homologues and unresolved matrix interferences point to the continuing need for good chromatographic separation to assure reliable identification and quantitation. Although the problem may be manageable for today’s small analyte lists, the challenge will inevitably grow as new PFAS compounds are added for investigational or regulatory purposes. We will show recent updates to our previous column comparisons while also discussing modifications to eluents and gradients. We will show that the use of alternative stationary phases of varying surface chemistry and eluents of varying polarity can significantly alter the sorption-elution characteristics of different classes of PFAS compounds. This orthogonal approach to PFAS HPLC chromatography should serve as a fruitful approach to future method development. As analyte lists increase in size and complexity, a variety of HPLC column chemistries and eluent compositions will be needed to accommodate the wide range of PFAS related compounds that might be encountered such as polar acids, non-polar acids, esters, amides, sulfonamides, and telomere length, all of which can be complicated with branched vs. linear isomers. The work presented here is illustrative and should be considered a starting point for column chemistry and mobile phase considerations for PFAS HPLC methodology.