Enhanced full-process method for the quantitative analysis of PFAS in sludge: Robust extraction and matrix effect-minimized method.

Accurate quantification of per- and polyfluoroalkyl substances (PFAS) in complex matrices, such as sewage sludge, is an ongoing challenge. To address this issue, a rigorously validated, robust, and efficient method for a wide range of PFAS (48 different species) extraction in sludge was developed. By optimizing liquid-solid ratio (30 mL/g), extracting solvent (methanol ammonia hydroxide (99.5 : 0.5, v/v)), oscillation time (60 min, 300 rpm), and pH of extraction solution (pH = 3) before solid phase extraction, an acceptable recovery (50 %-125 %) of the majority target PFAS (45 of 48) with low relative standard deviation (≤ 16.84 %) was achieved. Compared to currently widely used extraction methods, such as ASTM D2216, a Chinese standard (HJ 1334-2023) and the U.S. EPA method 1633A, the proposed method achieves a 17.3 %-27.6 % increase in the extracted total PFAS concentration for target analysis. Furthermore, it enables the identification of 3 additional PFAS types, thereby enhancing the scope and accuracy of PFAS analysis. During the investigation of matrix effects, despite the higher organic matter content in anaerobically digested sludge (71.8 %) compared to waste activated sludge (46.3 %), the matrix effect in the former was significantly lower during PFAS extraction and detection. This result suggests that unstable organic matter in sludge may primarily contribute to the observed matrix effects. Furthermore, reducing the injection volume during mass spectrometry analysis, diluting samples prior to detection, and applying internal standards correction can effectively mitigate matrix effects. When this method was applied to the analysis of different sludge samples (n = 10), all samples exhibited satisfied recoveries of internal standards within the range of 50 %-150 % except for long-chain 13C2-PFDoA in a sludge sample. Long-chain PFAS, such as PFOA and PFOS, remained the predominant compounds in different sludge. These findings highlight the method's reliability for complex matrices and its potential for broader environmental monitoring.