Mass spectrometric isomer characterization of perfluorinated compounds in technical mixture, water and human blood

Abstract

Perfluorinated compounds (PFC) are special surfactants which have been used since the 1950s. Their detection in the environment started at the beginning of the 2000s. A lot has to be explored in different fields such as method development, understanding of their environmental distribution, human exposure and their transport to remote areas such as the Artic region. No degradation pathways are known for perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), two predominant perfluorinated compounds in the biota and the environment. Their persistence in the environment emphasized the increasing interest of environmental scientists for this class of pollutant. In this work, besides method development, special attention was paid to the characterization of the isomers present in technical mixtures of PFC and in environmental samples. Methodologies and quantification Methodologies based on high performance liquid chromatography (HPLC) combined with mass spectrometry (MS) with electrospray in negative mode as ionization (ESI(-)) were developed for the analysis of perfluorinated compounds in biota. The extraction procedure consists of an ion pairing extraction using tetra-alkyl ammonium and methyl tert-butylether. Triple quadrupole (TQ) mass spectrometry was better suited for quantification compared to ion trap MS. TQMS enabled the detection of perfluorinated compounds in lower limits of detection (pg range) required for ultra trace analysis. The possibility of systematic errors of the applied methods was investigated. Possible artefacts in the analysis of perfluorinated compounds were identified. One major drawback was the risk of contamination originated by TEFLON®, which can contain perfluorocarboxylic acids. Matrix interference induced also ionization suppression/enhancement and emphasized the still need of method improvement. Moreover, the presence of by-products such isomers and homologues compounds in technical mixtures and in environmental samples make a proper quantification more difficult. Determination of isomer patterns in technical mixture Reversed phase chromatography was used to study the isomer composition of technical PFOS mixtures. Diperfluoromethyl, mono-perfluoromethyl substituted isomers and the linear isomer were identified. Seven isomers present in a technical PFOS mixture could be separated by HPLC. A new derivatization procedure was developed for PFOS and perfluorocarboxylic acids to allow high resolution gas chromatography (HRGC) separation by converting them into iso-propyl esters. An improvement of the separation of eleven PFOS isomers with a maximum of two coeluting isomers was achieved applying HRGC. It offers a promising alternative for the perfluorinated isomers separation in technical mixture. Structural elucidation of PFOS, PFOA and PFOSA monosubstituted isomers was possible applying tandem MS. It allowed the differentiation of up to ten isomers in a technical PFOS mixture. Ion trap tandem MS was more suitable to elucidate the position of the CF3 branching at the perfluorinated chain of monosubstituted PFOS isomers due to more structure-characteristic spectra. Tandem MS spectra of PFOA and perfluorooctanesulfonamide (PFOSA) monosusbtituted isomers were more complex. Only slight differences were observed between their MS/MS spectra due to a different charge stabilization. Currently, the lack of available pure isomer standards limits the isomerspecific analysis. Determination of isomer patterns in technical mixture, water and human blood Finally, the HPLC-MS method for isomer identification in technical mixtures was applied to water and human blood extracts. Isomer profile is indicative of the origin of PFAS contamination. Branched isomers are typical to an electrochemical fluorination (ECF) source, whereas mainly linear structures suggest a telomer source. PFOS detected in human blood collected in Sweden, Australia and United Kingdom was found to be produced by ECF process. However, the sources of PFOA in human were both an ECF and a telomerization processes. Moreover, the comparison of isomer pattern in human blood and water indicated different routes of exposure. The isomers present in technical mixtures were also present in environmental samples. These results showed the potential of isomer pattern for source characterization. This can be useful for risk assessment of humans and other living organisms. However, they could not be completely identified due to insufficient sensitivity. Improvement of the extraction procedure to lower matrix interferences is needed. The development of an alternative GC-MS method combined with a derivatization step could improve separation but not the detection limits due to low derivatization yield. Additional data about isomer patterns in different biota and human bloods from other geographic origins are required for comparison with present results.