RPLC-HILIC and SFC with Mass Spectrometry: Polarity-Extended Organic Molecule Screening in Environmental (Water) Samples

Abstract

Trace organic compounds are important in environmental analysis because they impact water quality and introduce potential (eco)toxicological effects. Current analytical methods mostly rely on gas chromatography (GC) or reversed-phase liquid chromatography (RPLC) coupled with (tandem) mass spectrometry. However, neither method can easily separate very polar molecules. This study presents two chromatographic separation strategies, a serial RPLC-hydrophilic interaction liquid chromatography (RPLC-HILIC) coupling and an analytical scale supercritical fluid chromatography (SFC) system, and validates their separation effectiveness as polarity-extended chromatographic methods for 274 environmentally relevant compounds. Compounds tested were grouped into three polarity classes, "very polar" {log D (pH 7) below -2.5}, "polar" {log D (pH 7) -2.5 to +2}, and "non-polar" {log D (pH 7) higher than +2}). Nearly all compounds could be retained in both systems with relative standard deviations of retention times (RT; n = 6) typically between 2 and 5%. Both techniques have considerable benefits when combined with accurate mass spectrometric detection. Molecules RT and accurate mass were recorded in a database for each set up. This information was used for compound screening measurements like "hidden-target screening" in complex environmental matrices (such as wastewater treatment plant effluents). Results of both techniques are complementary and useful for all types of molecules polarity. In this study, more than 80% of the compounds found in wastewater treatment plant effluent samples possessed a negative log D (pH 7) value. This result highlights the basic necessity to include "very polar" compounds in water monitoring techniques and protocols.

Persistent, mobile and toxic substances in the environment: a spotlight on current research and regulatory activities

“…The organic trace substances can have very different polarities, which thus require different analytical methods. The serial RPLC-HILIC coupling has proven to be optimal for the simultaneous analysis of very polar, polar and non-polar substances [29]. Studies were carried out, for example, in a river before and after the introduction of discharges of an STP as well as directly in the effluent.…”

Separation and detection of aqueous atmospheric aerosol mimics using supercritical fluid chromatography–mass spectrometry

“…Due to slow room temperature reaction times at these concentrations, the mixture was allowed to react for 6-7 weeks in a dark environment before analysis (Zhao et al, 2015). This ensured that the reaction had proceeded far enough to form previously identified major products (Amarnath et al, 1994;Bones et al, 2010;Sareen et al, 2010;De Haan et al, 2011;Lin et al, 2015;Kampf et al, 2016;Aiona et al, 2017;Hawkins et al, 2018).…”

“…In order to ensure that this system performs as well as comparable chromatography-mass spectrometry coupled systems, masses detected in this system were compared to those found in the literature for the methylglyoxal-ammonium sulfate system (Amarnath et al, 1994;Bones et al, 2010;Sareen et al, 2010;De Haan et al, 2011;Lin et al, 2015;Kampf et al, 2016;Aiona et al, 2017;Hawkins et al, 2018). Each of the masses in Table S3 were monitored.…”

Supercritical fluid chromatography – Mass spectrometry: Recent evolution and current trends

“…In addition, due to the high versatility of SFC-MS, it can be successfully employed for the simultaneous analysis of both hydrophilic and lipophilic molecules, from carbohydrates to lipids in metabolomics [76] (Fig. 5), from water to fat-soluble vitamins in food [79], and from highly hydrophilic to lipophilic trace organic compounds in environmental samples [80]. As more applications involving the use of SFC-MS with polar and highly polar compounds are arising, it can be stated that SFC-MS has now become a well-suited technique not only for lipophilic compounds, but also for those analytes whose polarity falls between -2 < log P >2.…”