Mass spectral studies towards more reliable measurement of perfluorooctanesulfonic acid and other perfluorinated chemicals (PFCs) in food matrices using liquid chromatography/tandem mass spectrometry

Abstract

Liquid chromatography/mass spectrometry (LC/MS) experiments are described, leading to a reliable method for the measurement of perfluorooctanesulfonic acid (PFOS) and other perfluorinated chemicals (PFCs) in foods. Separations were performed on new fluorinated stationary phases, RP Octyl (-C(8)F(17)) or propyl-perfluorobenzene (-C(3)H(6)-C(6)F(5)), to ensure resolution of PFOS and interfering taurohydroxycholate isomers. Aqueous ammonium formate (5 mM) and methanol were used as the mobile phases. The mass spectrometer was operated in negative electrospray ionisation mode, recording two transitions for each analyte and one for each internal standard. The purities of the analytical standards for the eleven target perfluoro analytes (C(7) to C(12) carboxylic acids, C(4), C(6) and C(8) sulfonic acids, and octanesulfonamide (PFOSA)) were found to be in close agreement with the supplied values; the lowest purity was 91%. Five candidate internal standards were investigated, (13)C(4)-PFOS, (13)C(4)-perfluorooctanoic acid, (13)C(2)-perfluorodecanoic acid, D(9)-n-ethylperfluorooctanesulfonamidoethanol (D(9)-n-Et-FOSE) and D(3)-n-methylperfluorooctanesulfonamide (D(3)-n-Me-FOSA); the purities were all >98%. The use of tetrahydro-PFOS generated backgrounds (>1 microg/kg) for perfluoroheptanoic acid and perfluorobutanesulfonic acid. Similarly D(9)-n-Et-FOSE was unacceptable and D(3)-n-Me-FOSA was volatile, leaving no clear candidate for normalisation of the measurement of PFOSA. Severe matrix-induced suppression and enhancement effects influenced ionisation, making external calibration and quantification problematic. This was addressed by a parallel standard addition and matrix-matching approach, comparing ionisation in methanol, in procedural blanks and in food-based extracts. The limits of detection (LODs) of 0.001-0.01 microg/kg in solvent and 0.01-1 microg/kg in foods demonstrate that this method is suitable for the determination of PFCs in all food to the required 1 microg/kg reporting level.

Tetrahydrofuran–water extraction, in-line clean-up and selective liquid chromatography/tandem mass spectrometry for the quantitation of perfluorinated compounds in food at the low picogram per gram level

“…The extraction method was validated by analysing flounder fillets previously used in the Second International Interlaboratory Study on PFCs [20] and containing the following concentrations of the target compounds, expressed as mean values and their standard deviations: 18.0 ± 4.1, 17.5 ± 4.6, 21.1 ± 4.6, 15.9 ± 4.1, 17.3 ± 5.2 and 150 ± 44 ng g −1 for PFOA, PFNA, PFDA, PFUdA, PFDoA and PFOS, respectively. Sample aliquots (10 g, wet weight) were freeze-dried and spiked with the corresponding mass-labeled PFCs (see Table 1 of Supplementary Data).…”

“…Only a limited number of methods are currently available to investigate dietary exposure to PFCs [10,11,20,21]. Food samples (1-10 g, wet weight) are usually serially extracted with medium-polar solvents such as methanol or acetonitrile, whether directly or following alkaline digestion.…”

Organic Contaminant Content and Physico-Chemical Characteristics of Waste Materials Recycled in Agriculture

“…The sample extraction procedure applied to PFASs is described by Lloyd et al [19]. Briefly, quadruple 1−10 g portions of each homogenised sample were transferred into Falcon tubes (50 mL).…”

Extraction of perfluorinated compounds from food matrices using fluorous solvent partitioning

“…The two systems were reanalysed with an additional cleanup stage, using weak anion exchange solid phase extraction (WAX-SPE) after fluorous extraction [8]. In order to quantify the matrix effects, the systems were each investigated in two experiments.…”

“…1). We have previously noted that the interferent is the natural abundance 13 C 1 -labelled form of a larger set of species dependent bile salt isomers at [M+1ÀH] À 499.297 [8].…”