Determination of perfluoroalkyl acid isomers in biosolids, biosolids-amended soils and plants using ultra-high performance liquid chromatography tandem mass spectrometry

Isomer-specific analysis of perfluoroalkyl acids (PFAAs) is important to accurately assess their environmental source, fate, and human risks. In this study, a method was developed for the determination of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorohexane sulfonate (PFHxS) isomers in biosolids, biosolids-amended soils and plants using ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The separation efficiencies of two chromatographic columns and extraction capacities of different methods were tested. Compared with the C18 column (ACQUITY UPLC BEH Shield RP18 column), the column with an alkyl perfluorinated C8 stationary phase (Epic FO LB column), in combination with the distinct MS/MS transitions of analytes, allowed better separation of most isomers. The ion-pair extraction method showed more effective matrix separation than that of the alkaline digestion method, with recoveries ranging from 79.6-105% for biosolids, 80.4-116% for soils, and 68.0-114% for plant tissues. The method detection limits ranged from 10 to 55, 3-13, and 8-58 pg/g dry weight for biosolids, soil, and plants, respectively. This method was applied successfully to quantify individual isomers in biosolids, biosolids-amended soils and plants. Six PFOA, eight PFOS, and two PFHxS isomers were found in the samples, with linear isomers being the dominant species. Further analysis revealed that the translocation potentials of branched isomers within plants were higher than those of linear isomers.