Determination of four regulated PFASs (PFOA, PFOS, PFNA, PFHxS) in drinking water by UHPLC-MS/MS with direct injection: development and validation of a rapid, “green” analytical procedure

Abstract

Per- and poly-fluoroalkyl substances (PFAS) are currently being widely used in various industrial applications; however, they represent an environmental and human health concern due to their persistence and bioaccumulation properties. This situation has stimulated the drafting of a European Directive (2020/2184), which regulates PFAS in drinking water. The regulation includes four PFAS of particular concern, whose concentrations must not exceed 20 ng/L as a sum: perfluorooctanoic acid (PFOA), perfluorooctanesulphonic acid (PFOS), perfluorononanoic acid (PFNA) and perfluorohexanesulphonic acid (PFHxS). Aim of this study was to develop and validate an original rapid and sensitive method, without any sample preparation and pre-concentration step, for monitoring the four target analytes in drinking water matrices by UHPLC-MS/MS. Water samples were just diluted 1:1 (v/v) with methanol, filtered and directly injected into the analytical system. The method was validated in real drinking water over 0.5-600 ng/L concentration range. Results showed good linearity for all the target analytes (R²>0.9950). Accuracy, expressed as recovery and evaluated at three concentration levels, ranged within 96.9-114% with RSD < 12.9%. Despite the direct injection, good method detection limits (MDL) were achieved: 0.19 ng/L < MDL < 0.28 ng/L and lower limit of quantification was 0.5 ng/L for all analytes. The validated method was applied to 12 real drinking water samples from North – East Italy. PFOA, PFOS and PFHxS were detected in some samples, while PFNA was never detected. The sum of the four PFAS’ concentrations was below the regulatory threshold of 20 ng/L in all samples.