► Retention behavior of structural related benzoic acids on a sulfobetaine phase in ZIC-HILIC. ► The retention is due to number, position and H-bond properties of the functional groups. ► Benzoic ...acids retention is well described by partition-like models. ► Adsorption-like processes contribute to the retention of analytes with H-donor groups. ► ACN and salt content in the mobile phase affect the thickness of the water layer in which partition takes place.
The retention behavior of fifteen isomeric hydroxy- and aminobenzoic acids in zwitterionic hydrophilic interaction chromatography was studied using a sulfobetaine phase (ZIC-HILIC). By an inspection of their molecular structures, the retention was related to the number, the position and hydrogen bond properties of the functional groups. The effect of the chromatographic conditions was analyzed in order to investigate the retention mechanism of the stationary phase. The increased retention observed for negative charged compounds when the mobile phase pH decreased was ascribed to a diminishing of the electrostatic repulsion with the underivatized silanol groups. Also the salt buffer concentration in the mobile was proved to have a great influence in the modulation of the electrostatic interactions. However, the retention behavior of the benzoic acids was not described by conventional ion-exchange models. Subsequently, a systematical analysis of partition, adsorption, and hydrophilic chromatographic models was presented. The results from the fittings indicated that partition processes govern mainly the ZIC-HILIC separation, but also adsorption processes via hydrogen bonds occurred for hydrogen donor analytes. Finally, the influence of the chromatographic conditions on the water enriched layer in which partition takes place has been evaluated by the elution behavior of toluene.
Untargeted analysis of a composite house dust sample has been performed as part of a collaborative effort to evaluate the progress in the field of suspect and nontarget screening and build an ...extensive database of organic indoor environment contaminants. Twenty-one participants reported results that were curated by the organizers of the collaborative trial. In total, nearly 2350 compounds were identified (18%) or tentatively identified (25% at confidence level 2 and 58% at confidence level 3), making the collaborative trial a success. However, a relatively small share (37%) of all compounds were reported by more than one participant, which shows that there is plenty of room for improvement in the field of suspect and nontarget screening. An even a smaller share (5%) of the total number of compounds were detected using both liquid chromatography–mass spectrometry (LC-MS) and gas chromatography–mass spectrometry (GC-MS). Thus, the two MS techniques are highly complementary. Most of the compounds were detected using LC with electrospray ionization (ESI) MS and comprehensive 2D GC (GC×GC) with atmospheric pressure chemical ionization (APCI) and electron ionization (EI), respectively. Collectively, the three techniques accounted for more than 75% of the reported compounds. Glycols, pharmaceuticals, pesticides, and various biogenic compounds dominated among the compounds reported by LC-MS participants, while hydrocarbons, hydrocarbon derivatives, and chlorinated paraffins and chlorinated biphenyls were primarily reported by GC-MS participants. Plastics additives, flavor and fragrances, and personal care products were reported by both LC-MS and GC-MS participants. It was concluded that the use of multiple analytical techniques was required for a comprehensive characterization of house dust contaminants. Further, several recommendations are given for improved suspect and nontarget screening of house dust and other indoor environment samples, including the use of open-source data processing tools. One of the tools allowed provisional identification of almost 500 compounds that had not been reported by participants.
The focus of this study was to investigate the efficacy of applying boron-doped diamond (BDD) electrodes in an electrochemical advanced oxidation process, for the removal of the target compound ...diclofenac (DCF) in different water matrices. The reduction of DCF, and at the same time the formation of transformation products (TPs) and inorganic by-products, was investigated as a function of electrode settings and the duration of treatment. Kinetic assessments of DCF and possible TPs derived from data from the literature were performed, based on a serial chromatographic separation with reversed-phase liquid chromatographyfollowed by hydophilic interaction liquid chromatography (RPLC-HILIC system) coupled to ESI-TOF mass spectrometry. The application of the BDD electrode resulted in the complete removal of DCF in deionized water, drinking water and wastewater effluents spiked with DCF. As a function of the applied current density, a variety of TPs appeared, including early stage products, structures after ring opening and highly oxidized small molecules. Both the complexity of the water matrix and the electrode settings had a noticeable influence on the treatment process’s efficacy. In order to achieve effective removal of the target compound under economic conditions, and at the same time minimize by-product formation, it is recommended to operate the electrode at a moderate current density and reduce the extent of the treatment.
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.
In the present study, an easy and efficient method based on the serial coupling of analytical reversed‐phase and zwitterionic hydrophilic interaction liquid chromatography was developed for the ...simultaneous separation of polar and nonpolar phenols occurring in wine. The zwitterionic hydrophilic column was connected in series to the reversed‐phase one via a T‐piece, with which the ACN content in eluent of the second dimension was increased, in order to cope the solvent strength incompatibility between the two columns. The final mobile phase at low‐flow rate (≤0.5 mL/min), high‐ACN content (90%), and low‐salt concentration was directed to an ESI‐TOF‐MS , for high accurate mass detections. The developed method was applied for the identification of target phenols in several wines. Retention time and peak width intra‐ and interday repeatability studies proved the reliability of the method for the simultaneous analysis of all the polar and nonpolar analytes in wine. The serial reversed‐phase/zwitterionic hydrophilic interaction liquid chromatography coupling offered the possibility to enlarge the number of identified compounds and it represents a valid approach for nontarget analysis of complex samples by a single injection.
In this article, a dataset from a collaborative non-target screening trial organised by the NORMAN Association is used to review the state-of-the-art and discuss future perspectives of non-target ...screening using high-resolution mass spectrometry in water analysis. A total of 18 institutes from 12 European countries analysed an extract of the same water sample collected from the River Danube with either one or both of liquid and gas chromatography coupled with mass spectrometry detection. This article focuses mainly on the use of high resolution screening techniques with target, suspect, and non-target workflows to identify substances in environmental samples. Specific examples are given to emphasise major challenges including isobaric and co-eluting substances, dependence on target and suspect lists, formula assignment, the use of retention information, and the confidence of identification. Approaches and methods applicable to unit resolution data are also discussed. Although most substances were identified using high resolution data with target and suspect-screening approaches, some participants proposed tentative non-target identifications. This comprehensive dataset revealed that non-target analytical techniques are already substantially harmonised between the participants, but the data processing remains time-consuming. Although the objective of a “fully-automated identification workflow” remains elusive in the short term, important steps in this direction have been taken, exemplified by the growing popularity of suspect screening approaches. Major recommendations to improve non-target screening include better integration and connection of desired features into software packages, the exchange of target and suspect lists, and the contribution of more spectra from standard substances into (openly accessible) databases.
Graphical Abstract
Matrix of identification approach versus identification confidence
The analytical hyphenation of micro-flow high-performance liquid chromatography (LC), with post-column liquid mixing and mass spectrometric detection (MS) was established to detect partially oxidized ...polycyclic aromatic hydrocarbons (oxy-PAHs) for low quantity samples. 100
pmol injections of 30 reference standards could be detected in good sensitivity using either atmospheric pressure chemical ionization (APCI) and/or atmospheric pressure photoionization (APPI). The connected mass spectrometer was a single quadrupol analyzer realizing simultaneous registration of positive and negative ions in scan range width of 200–300
Da. The ionization efficiency was compared using three ionization sources (incl. electrospray ionization (ESI)) for several oxy-PAHs. According to the mass spectra, the analytes behave differently in ionization properties. Ionization mechanism (e.g. deprotonated ions and electron captured ions) could be discussed with new inside views. Finally, the hyphenated system was applied to an exemplary aerosol extract and thus highlighting the expedient utilization of this downscaled method for real samples.
Human pharmaceuticals and their residues are constantly detected in our waterbodies, due to poor elimination rates, even in the most advanced waste water treatment plants. Their impact on the ...environment and human health still remains unclear. When phytoremediation is applied to aid water treatment, plants may transform and degrade xenobiotic contaminants through phase I and phase II metabolism to more water soluble and less toxic intermediates. In this context, peroxidases play a major role in activating compounds during phase I via oxidation. In the present work, the ability of a plant peroxidase to oxidize the human painkiller diclofenac was confirmed using stopped flow spectroscopy in combination with LC-MS analysis. Analysis of an orange colored product revealed the structure of the highly reactive Diclofenac-2,5-Iminoquinone, which may be the precursor of several biological conjugates and breakdown products in planta.
•First report of a plant peroxidase oxidizing the human painkiller diclofenac.•Enzymatic reaction followed by stopped flow spectroscopy.•Identification of Diclofenac-2,5-Iminoquinone by LS-MS/MS and TOF high resolution MS with accurate mass determination.
Highly polar trace organic compounds, which are persistent, mobile, and toxic (PMT) or are very persistent and very mobile (vPvM) in the aquatic environment, may pose a risk to surface water, ground ...water, and drinking water supplies. Despite the advances in liquid chromatography-mass spectrometry, there often exists an analytical blind spot when it comes to very polar chemicals. This study seeks to make a broad polarity range analytically accessible by means of serially coupling reversed-phase liquid chromatography (RPLC) and hydrophilic interaction liquid chromatography (HILIC) to high-resolution mass spectrometry (HRMS). Moreover, a workflow is presented using optimized data processing of nontarget screening (NTS) data and subsequently generating candidate lists for the identification of very polar molecules via an open-access NTS platform and implemented compound database. First, key input parameters and filters of the so-called feature extraction algorithms were identified, and numerical performance indicators were defined to systematically optimize the data processing method. Second, all features from the very polar HILIC elution window were uploaded to the STOFF-IDENT database as part of the FOR-IDENT open-access NTS platform, which contains additional physicochemical information, and the features matched with potential compounds by their accurate mass. The hit list was filtered for compounds with a negative log
D
value, indicating that they were (very) polar. For instance, 46 features were assigned to 64 candidate compounds originating from a set of 33 samples from the Isar river in Germany. Three PMT candidates (e.g., guanylurea, melamine, and 1,3-dimethylimidazolidin-2-one) were illustratively validated using the respective reference standards. In conclusion, these findings demonstrate that polarity-extended chromatography reproducibly retards and separates (very) polar compounds from surface waters. These findings further indicate that a transparent and robust data processing workflow for nontarget screening data is available for addressing new (very) polar substances in the aqueous environment.
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