Application of New Fuorine-Containing Matrix in the Determination of Perfluorosulfonic Acids by Matrix Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry

Based on Witting reaction, a novel matrix 1,1-bis(3-fluorophenyl) ethylene (EDF) was prepared for the analysis of acidic small molecules, and the structure of EDF was confirmed by NMR and MS. A appropriate amount of EDF was dissolved in dichloromethane, following by vortex oscillation for 5 min to prepare 1 g·L^-1 EDF matrix solution. The hamburger wrapping paper of food grade packaging material was cut into 0.5 cm×0.5 cm fragments, and 100.00 mg of fragments were extracted ultrasonically at room temperature for 2 h in 5 mL of methanol. The extract was passed through a 0.22 μm filter membrane to obtain the sample solution to be tested. Layer by layer sampling method was adopted:0.6 μL of EDF matrix solution was transferred to the circular point of stainless steel target plate quickly, and EDF matrix with dichloromethane as solvent evaporated rapidly. Because of its low boiling point and small amount, it just covered the range of circular point. 0.8 μL of the sample solution to be tested was moved to the same position of the stainless steel target plate. After it was evaporated naturally, the sample was analyzed by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Its detection performance for perfluorooctane sulfonate (PFOS) and perfluorobutane sulfonate (PFBS) were compared with common matrices including 9-aminoacridine (9-AA), α-cyano-4-hydroxycinnamic acid (CHCA) and 1,6-diphenyl-1,3,5-hexatriene (DPH). As shown by the results, EDF could achieve similar signal intensity, but the background was much cleaner without matrix interference peak. Using EDF as matrix and eicosanoic acid as internal standard, the linear ranges of PFOS and PFBS standard curves were both 20-250 μg·L^-1, with the same detection limits (3S/N) of 1 μg·L^-1. Test for recovery was made on the actual packaging paper sample by standard addition method, giving results in the range of 90.3%-108%, and RSDs (n=7) of the determined values were within 30%. It was shown that EDF matrix had ideal detection results and was suitable for the determination of perfluorosulfonic acids in packaging materials.