Screening for Polar Chemicals in Water by Trifunctional Mixed-Mode Liquid Chromatography–High Resolution Mass Spectrometry

The
presence of persistent and mobile organic contaminants (PMOC)
in aquatic environments is a matter of high concern due to their capability
of crossing through natural and anthropogenic barriers, even reaching
drinking water. Most analytical methods rely on reversed-phase liquid
chromatography (RPLC), which is quite limited for the detection of
very polar chemicals. Thus, many of these PMOCs may have not been
recognized as water pollutants yet, due to the lack of analytical
methods capable to detect them. Mixed-mode LC (MMLC), providing the
combination of RP and ion-exchange functionalities is explored in
this work with a trifunctional column, combining RPLC, anion and cation
exchange, which allows the simultaneous determination of analytes
with extremely different properties. A nondiscriminant sample concentration
step followed by a MMLC-high resolution mass spectrometry method was
developed for a group of 37 very polar model chemicals with different
acid/base functionalities. The overall method performance was satisfactory
with a mean limit of detection of 50 ng/L, relative standard deviation
lower than 20% and overall recoveries (including matrix effects) higher
than 60% for 54% of model compounds. Then, the method was applied
to 15 real water samples, by a suspect screening approach. For those
detected PMOC with standard available, a preliminary estimation of
concentrations was also performed. Thus, 22 compounds were unequivocally
identified in a range of expected concentrations from 6 ng/L to 540
μg/L. Some of them are well-known PMOC, such as acesulfame,
perfluorobutanoic acid or metformin, but other novel pollutants were
also identified, as for example di-o-tolylguanidine or trifluoromethanesulfonic
acid, which had not or were scarcely studied in water so far.