Improvement of the Method Detection Limit Listed in EPA 1633 for PFAS

Per- and Polyfluoroalkyl Substances (PFAS) in the Environment
Poster Presentation

Presented by R. Marfil-Vega
Prepared by M. Davis, O. Shrestha, K. Luo, L. Wiest
Shimadzu Scientific Instruments, 7102 Riverwood Drive, Columbia, MD, 21046, United States


Contact Information: [email protected]; 410-910-0884

ABSTRACT

Per- and poly-fluoroalkyl substances (PFAS) present unique analytical challenges, including the need for achieving detection limits at ultra-trace levels on a routine basis. EPA finalized the 1633 method in January 2024; however, it was finalized for aqueous matrices (wastewater, surface water, and groundwater) in July 2023. This study aims to demonstrate how to improve the method detection limits listed in EPA 1633 for aqueous samples among other selected quality control parameters utilizing the Shimadzu’ LCMS-8060NX. Three batches of solid phase extraction (SPE) and LC-MS/MS analyses were performed daily over 3 days comprising 7 spiked samples and 7 method blanks. This analysis used Shim-pack Scepter C18-120 (3 µm) columns as delay (50 mm) and analytical (100 mm) columns with 2.1 mm inner diameters. Overall, all compounds met the RSE criteria (<20%) for instrument linearity. This linear range varied for PFAS target compounds from 0.025 µg/L to 25 µg/L with a resulting RSE range from 9.8% for PFTrDA to 18.3% for PFHxA. EIS compounds had an RSE range from 0.71% for 13C9-PFNA to 10.92% for 13C3-HFPO-DA at concentration levels specified by the method. Seven water samples and method blanks were spiked at concentrations 10x lower than the limits of quantification (LOQ) required by EPA method 1633. Guidelines from 40 CFR 136, Appendix B were followed to calculate the MDL values.. Final MDL values were then determined based on the greater value between the calculated MDL in spiked samples (MDLs) and method blanks (MDLb). MDLb was quantified for 21 out of the 40 targets; however, for only one (PFHpA) the MDLb (0.23 ng/L) was greater than its MDLs (0.16 ng/L). Overall, the final MDLs were 1.5x to 10x better than those listed in EPA 1633. In this presentation we will share the optimized method and detailed discussion of the MDL results.