Novel non-targeted analysis of perfluorinated compounds using fluorine-specific detection regardless of their ionisability (HPLC-ICPMS/MS-ESI-MS)

Although perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) have been phased out, there is a plethora of per- or polyfluoroalkyl substances (PFAS) generated and only a small number of these compounds are currently being monitored in environmental and biological sample using molecular mass spectrometry (MS). Total fluorine determination has revealed that a substantial amount of fluorinated organic compounds has not been identified. Due to the small mass deficiency of fluorine, it is not an easy task to screen successfully all fluorinated compounds including those which are not easy ionisable, hence a novel fluorine-specific detector is needed. Here, inductively-coupled plasma mass spectrometry (ICPMS) was used for the first time for the detection of PFAS, by using the novel approach to transfer F- into a detectable [BaF]+ in the argon plasma. A reverse phase-high performance liquid chromatography (RP-HPLC) method was developed and then online coupled to ICPMS/MS for the fluorine-specific detection and simultaneously to electrospray MS (ESI-MS) to separate perfluorinated carboxylic acids (PFCA) and perfluorooctanesulfonic acid (PFOS). The calibration was linear and was element-specific with detection limits of 0.49 mg F L-1 under gradient elution method. As a proof of concept, PFCA standards in methanol were not fully neutralised to force the esterification and those solutions were measured using HPLC-ICPMS/MS-ESI-MS. The methyl esters were not detectable by ESI-MS but by ICPMS/MS. This illustrates that the undetectable fluorine-containing compounds were detected and quantified by the element-specific detection of ICPMS/MS. The analysis of spiked river water at sub-ppb level gave an acceptable recovery using a SPE-based preconcentration method. Since ICPMS/MS method is an element-specific detection, all non-fluorinated compounds interfering in ESI-MS were eliminated. Hence, HPLC-ICPMS/MS can be used as a non-targeted method of fluorinated compounds which helps the identification of novel fluorinated compounds in environmental and biological samples and helps with mining the ESI-MS data.