Elīna Pasečnaja, PhD

TITLE: LC-MS/MS Determination of PFAS in Wild Baltic Grey Seal Plasma - Step by Step Workflow Development Per-and polyfluoroalkyl substances (PFAS) are persistent environmental contaminants that require sensitive and selective analytical methods for reliable quantification in complex biological matrices. Wildlife plasma presents additional analytical challenges due to limited sample availability, high protein and lipid content, matrix effects, and the risk of background PFAS contamination. An LC-MS/MS workflow was developed for the determination of PFAS in wild Baltic grey seal plasma. Initial screening of 31 PFAS in pooled seal pup plasma was used to evaluate compound occurrence and select 10 target analytes for subsequent quantitative method development. The workflow was systematically optimized with particular emphasis on minimizing sample consumption, reducing matrix-related effects and analytical background, and achieving robust chromatographic and mass spectrometric performance. The optimized method enabled quantitative analysis using only 50 µL of plasma and demonstrated stable chromatographic performance, an LOQ of 0.8 ng/mL for all target compounds, intra-day precision below 10% RSD, and recoveries of 75-125%. The method was subsequently applied to plasma samples from wild Baltic grey seal pups and adults collected in Estonia. The resulting PFAS concentration profiles supported evaluation of age- and sex-dependent exposure patterns and demonstrated the applicability of the developed workflow to wildlife biomonitoring using limited-volume, complex biological samples.