Comparison of per- and polyfluoroalkyl substance (PFAS) soil extractions and instrumental analysis: large-volume injection liquid chromatography-mass spectrometry, EPA Method 1633, and commercial lab results for 40 PFAS in various soils

Quantifying per- and polyfluoroalkyl substances (PFAS) in soil is a crucial part of site evaluations. Several methods are currently used in commercial and academic labs to evaluate PFAS-affected soils, with differences in extraction solvent, extraction method, cleanup procedure, and instrumental analysis among laboratories. This study aims to compare the accuracy and efficiency of a legacy in-house soil extraction method for PFAS with EPA Method 1633 for sample extraction and analysis using liquid chromatography tandem mass spectrometry (LC-MS/MS). An aqueous film-forming foam (AFFF)-impacted field soil (Soil A), a "clean soil" (Ottawa sand), and a certified reference soil were subjected to both extraction methods. Subsamples of these soils were also submitted to an accredited commercial lab. The commercial lab analyzed samples in accordance with EPA Method 1633 both for extraction and analysis. For comparison, our lab extracted the samples with both EPA Method 1633 and the in-house legacy soil extraction method, followed by a large-volume injection (LVI) adaptation of EPA Method 1633 instrumental analysis method. The EPA Method 1633 followed by LVI analysis quantified slightly more compounds without quality control flags than the legacy extraction method followed by LVI analysis for Soil A and the certified reference soil. Both in-house extractions had 76% of reportable compound concentrations within ± 15% relative standard deviation. The commercial small-volume injection results returned the least number of quality control flags, but quantified fewer compounds at low concentrations. Considering the time and cost of EPA Method 1633 and commercial analysis, this study supports the suitability of the legacy soil extraction method with LVI LC-MS/MS analysis for in-house soil analysis with comparable results to EPA Method 1633 as well as commercial analysis.