Determination and Elimination of Matrix Effect in Analysis of Perfluorinated Acids Using High Performance Liquid Chromatography-Negative Electrospray Tandem Mass Spectrometry

Matrix effects, ionization enhancement or suppression, are always possible with the electrospray ionization technique and can significantly hamper the analysis of PFAs in complex environmental matrixes. The objective of this study is to determine and eliminate the matrix effects in analysis of sewage using high performance liquid chromatography-negative electrospray tandem mass spectrometry (HPLC-negative ESI-MS/MS). Standard addition, which involves spiking successive known quantities of a standard into the sample extracts and reanalyzing, are used for determination of the matrix effects, while correction using isotopically labeled internal standards and clean-up of sample extracts using dispersive carbon sorbent are used for elimination of matrix effects. The results indicate that ultra-short- (C2-3) and long-chain PFCAs (>C10) suffer ionization suppression, while medium-chain PFCAs (C4-10) and PFBS experience ionization enhancement; however, PFHxS and PFOS do not suffer significant matrix effects. Although internal standards, MPFOA and MPFOS, can effectively negate matrix effects for medium-chain PFCAs (C7-10), they are not suitable for some short- (<C7 PFCAs and PFBS) and long-chain PFAs (>C10 PFCAs), which are eluted significantly earlier or later than their retention times, respectively. However, matrix effects of all analytes are significantly naegated by dispersive carbon sorbent because it can effectively remove the co-eluting interference compounds from SPE elution but not affect PFAs.