Direct Determination of 23 Kinds of Per- and Polyfluoroalkyl Substances in Crude Plant Extracts by Liquid Chromatography-Tandem Mass Spectrometry Coupled with Online Solid Phase Extraction

A new method for simultaneous determination of 23 kinds of per- and polyfluoroalkyl substances (PFASs) (13 kinds of perfluoro carboxylic acids, 4 kinds of perfluoro sulfonic acids, and 6 kinds of new substitutes) in plant leaf tissue by ultra -high performance liquid chromatography -tandem mass spectrometry (UHPLC-MS/MS) using automatic online solid phase extraction (SPE) to remove the matrix interference components in plant crude extracts was developed. The plant leaf samples were extracted twice with 1% formic acid -methanol solution, then evaporated to dry, redissolved with 70% methanol solution, and directly injected for analysis. After 23 kinds of target PFASs were purified automatically by online SPE with a WAX column, the six -way valve was switched to rinse PFASs onto an alkaline mobile phase system -compatible C18 analytical column. Then, the 23 kinds of target PFASs were separated within 16 min by gradient elution using a binary mobile phase system of methanol/water (Containing 0.4% ammonium hydroxide). Tandem mass spectrometry was performed in multiple reaction monitoring (MRM) mode for online detection of various PFASs, and quantification was carried out by internal standard method. The results of the method validation showed that satisfactory average recoveries of 23 kinds of PFASs in plant leaf samples (64.2%-125.5%), precision (relative standard deviations (RSDs) of 0.7%-12.8%), linearity (R-2>0.990), and sensitivity (the detection limits (S/N=3) were in the range of 0.02-0.50 mu g/kg) were achieved. Finally, this method was used to detect PFASs in the marine green tide algae (Enteromorpha prolifera) and several tree leaves, and a total of 6 kinds of PFASs were detected, in which PFBA was the main contaminant. Compared with the reported offline SPE methods, the proposed online SPE technique significantly simplified the sample pretreatment process and provided an automatic, simple, and environment -friendly method for the routine monitoring of legacy and emerging PFASs in plant tissues.