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

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.