Emerging environmental contaminants will feature prominently at the upcoming HPLC 2018 conference, with presentations highlighting the latest advances in analysis of contaminants, such as per- and polyfluoroalkyl substances (PFASs), nanomaterials, microplastics, artificial sweeteners, 1,4-dioxane, pharmaceuticals, hormones, disinfection by-products (DBPs), sunscreens/UV filters, flame retardants, benzotriazoles, naphthenic acids, algal toxins, ionic liquids, and halomethane sulfonic acids. These contaminants are now frequently found in environmental and recreational waters, as well as in air, soil, sediment, and biota, including human blood (1). The fate of contaminants in the environment is a hot topic because many are transported globally and can transform into chemicals with altered toxicity. The development of sensitive analytical tools is key for identification and measurement of trace contaminants because environmental samples are inherently complex mixtures. High resolution (HR)-mass spectrometry (MS) is currently the most popular tool for non-target environmental analysis, with quantification limits now commonly at sub- to low-ng/L levels. Mass spectrometer developers continue to improve instrument resolution, with time-of-flight (TOF), Orbitrap, and quadrupole-(Q)-TOF mass spectrometers ranging from 30,000 to >100,000 resolution, a necessity for the determination of molecular formulas for unknown chemicals.
Innovations in chromatography continue to aid analysis, with high performance liquid chromatography (HPLC) and ultra-performance liquid chromatography (UPLC)-MS now commonplace for analyzing emerging contaminants, many of which are highly polar or have a high molecular weight, while gas chromatography (GC) and GC×GC are often used for volatile and semi-volatile contaminants. Innovations in recent years include the coupling of multiple LC and GC columns of different phases to improve separations of complex environmental mixtures. The coupling of C18 and hydrophilic interaction liquid chromatography (HILIC) columns with MS can allow the detection of significantly more compounds than a traditional single HPLC-MS/MS approach. For example, a recent study highlights the identification of more than 600 peptides in drinking water (2). Ion mobility-MS is also beginning to play an important role in environmental separations. An addition to classical chromatographic separations, ion mobility-MS offers another degree of separation by measuring differences in the cross-sections of molecules, a property of their three-dimensional shape. Recent applications of ion mobility-MS with HPLC-MS and UPLC-MS include the identification of artificial sweetener transformation products and naphthenic acid ozonation products. The development of new workflows, software, and library databases is a popular trend to tackle difficult analyses of hundreds or thousands of contaminants in environmental samples. These tools help automate and streamline the identification of compounds, enabling feature detection and tentative identifications in minutes. Though electron ionization (EI)-MS libraries have been widely available for years, electrospray ionization (ESI)-MS(/MS) libraries have yet to be organized for wide application. Fortunately, two commercial MS/MS libraries are now available – NIST and Wiley – which contain >15,000 and >1,200 compounds, respectively. And many open or semi-open MS databases, including the Human Metabolome Database (HMDB), Metlin, mzCloud, and MassBank, are also available. New workflow tools include Metfrag (a metabolomics MS/MS fragmentation predictor), CFM-ID, which predicts MS/MS spectra, and CFM-EI, which can predict EI mass spectra.
Finally, a tool called precursor ion exclusion (PIE) enables the automated detection and identification of low-abundance compounds in HPLC-MS/MS analyses of complex environmental mixtures (because low-abundance compounds are often the most interesting!). This technique overcomes a weakness of data dependent acquisition (DDA) by performing a second MS/MS scan that excludes the high-abundance ions identified in the initial scan. Thus, PIE focuses on lower-abundance ions, which would often be missed in a traditional HPLC-MS/MS analysis. This is just a snapshot of the exciting innovations happening in the world of emerging contaminants – join us at HPLC 2018 for more from the cutting edge of environmental research.
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References
- SD Richardson, TA Ternes, “Water analysis: emerging contaminants and current issues”, Anal Chem, 90, 398-428 (2018). Y Tang et al., “Non-targeted analysis of peptides and disinfection byproducts in water”, J Environ Sci, 42, 259−266 (2016).