PFAS Analysis Based Upon a pH-Variable LC Mobile Phase Gradient

Polyfluoroalkyl Substances (PFAS) in the Environment
Oral Presentation

Prepared by D. Schiessel1, D. Kennedy2, R. Jack2, S. Lodge2
1 - Babcock Laboratories, Inc., 6100 Quail Valley Court, Riverside, California, 92507, United States
2 - Phenomenex, Inc., 411 Madrid Ave., Torrance, California, 90501, United States


Contact Information: dschiessel@babcocklabs.com; (951) 653-3351


ABSTRACT

Current EPA methods 537, 537.1 and 533 are applicable only to drinking water and are limited to a small fraction of the thousands of known PFAS compounds. However, as matrices become more complex and analyte lists inevitably grow larger, a framework needs to be established to scale PFAS analysis to allow for the widest range of analyte chemistries. Although more standardized methods are needed using other techniques (e.g: GC-MS/MS), this presentation we will demonstrate one such framework specifically for PFAS analysis by LC-MS/MS. This framework is based upon the use of a variable pH mobile phase gradient, which could facilitate the expansion of PFAS analyte lists beyond current analyte target lists. The majority of methods used for PFAS analysis use an eluent system of ammonium acetate (NH4OAc), usually between 2 and 20mM at a pH of 7. This is a primary limitation of the existing methods when trying to scale the analyte list to include shorter chain PFAS. Both EPA methods 537.1 and 533 specify a 20mM NH4OAc, but the method flexibility allows for alternate mobile phases. While this flexibility can be useful when trying to discriminate analytes from matrix interference in drinking water extracts, it can be a larger advantage when analyzing more complex matrices derived from soil, sludge, and wastewater.
In this presentation we present data that demonstrate the utility of a pH gradient mobile phase for PFAS analysis that allows the analyst to widen the scope of analyte chemistry to properly chromatograph short chain and long chain PFAS as well as change the selectivity of the method. This holds true for any analyte panel outside the scope of method EPA 537.1 and EPA 533, in that the absolute and relative retention of some analytes are significantly different than when using a standard organic gradient with ammonium acetate (NH4OAc). This solution provides the ability to move early eluting components away from interferences and high ion suppression zones at the beginning of the chromatographic run. It may also allow for the inclusion of other PFAS analytes with a minimal redevelopment and optimization. Moving forward, this promising mobile phase gradient approach could be combined with work investigating alternative HPLC stationary phases to determine optimal conditions for PFAS panels that are much broader in scope and chemistry.