Elsevier

Journal of Chromatography A

Volume 1345, 6 June 2014, Pages 86-97
Journal of Chromatography A

Ultra-high performance liquid chromatography–quadrupole time-of-flight mass spectrometry to identify contaminants in water: An insight on environmental forensics

https://doi.org/10.1016/j.chroma.2014.04.017Get rights and content

Highlights

  • Non-target screening using LC–QqTOF-MS by ion extraction against a database.

  • Information dependent acquisition (IDA) of the MS/MS spectra confirms identity against a library.

  • PCA helps to establish the key compounds to distinguish between the different samples.

  • Calculation of the most probable empirical formula identifies relevant unknown.

  • Quantitative performance for targets is similar to that obtained with triple quad.

Abstract

Ultra-high pressure liquid chromatography–quadrupole time-of-flight mass spectrometry (UHPLC–QqTOF-MS) acquiring full scan MS data for quantification, and automatic data dependent information product ion spectra (IDA-MS/MS) without any predefinition of the ions by the user was checked for identifying organic contaminants in water samples. The use of a database with more than 2000 compounds achieved high confidence results for a wide number of contaminants based upon retention time, accurate mass, isotopic pattern and MS/MS library searching. More than 20 contaminants, mostly pharmaceuticals, but also mycotoxins and polyphenols were unambiguously identified. Furthermore, the combination of statistical data analysis using principal component analysis (PCA) followed by empirical formula calculation, on-line database searching and MS/MS fragment ion interpretation achieves not only the successful detection of unknown contaminants but also the selection of those relevant to different types of waters. Unknown compounds, such as C20H34O3, were identified in waste water showing the prospects of this technique. A group of 42 currently used pesticides were selected as target compounds to evaluate the quantitative possibilities. Mean recoveries and percentage relative standard deviation (RSD) were 48–79% (4–20% RSD). The limit of detections ranged from 0.02 to 2 ng L−1, with a validated limit of quantification of 2 ng L−1 for water after solid-phase (SPE) isolation and concentration. The quantitative data obtained using UHPLC–QqTOF-MS were compared with those obtained using conventional LC–MS/MS with a triple quadrupole (QqQ).

Introduction

In the last years, a large number of compounds, known as “emerging”, have been pointed out as possible environmental contaminants [1], [2], [3]. Pesticide residues are one of the most frequently detected compounds in water analysis [4], [5], [6]. However, water contamination is not limited to them but also includes pharmaceuticals, illicit drugs, personal care products and other substances from the human activity [1], [4], [7], [8], [9]. Not only constant and comprehensive monitoring of organic trace substances is essential to protect the quality of water [10] but also determine the possible sources of them, estimating the approximate timing of its release and distribution into the environment and appropriation of the liability for the damages among the sources (the so called environmental forensics) [11]. The standard technique in modern screening for medium-polar and polar substances is liquid chromatography–mass spectrometry (LC–MS) [10] with several mass analyzers, such as ion trap, triple quadrupole (QqQ), quadrupole linear ion trap (QTRAP), time-of-flight (TOF) or orbitrap [12]. The traditional target screening, in which the analytes are previously selected and any other contaminant present in the sample becomes undetectable [10], is currently the most common and well-established approach able to quantify hundreds of contaminants in a single run [13], [14], [15], [16], [17], [18], [19].

However, in recent years, there is a growing movement to analyze water beyond target compound list, and a shift towards non-targeted or general unknown screening that detects all the substances accessible for a particular technique [16], [20], [21], [22]. Both, TOF and QqTOF have already been used for screening of non-target and/or unknown compounds in different matrices [23], [24], [25], [26]. Although the gain in popularity and the increasing demand for retrospective and non-targeted analyses, there are still few methods in the literature that use full-scan mode to screen for non-target compounds in waste and surface waters [4], [7], [10], [27], [28]. In this sense, the QqTOF technology combines the best attributes of a QqQ and accurate mass TOF analyzers in a single instrument allowing high confidence identification based on MS and MS/MS information [29]. Therefore, acquired chromatograms are very rich in information and can easily contain thousands of ions from any compound present in the sample. In return, powerful software tools are needed to explore such data to identify unexpected compounds [30]. These tools are within the “omics” and “fingerprint” terms, and include amenable software, calculations, databases searching and statistical analysis that help in understanding the differences and the significance of the quantified pollutants that give rise to these differences. Recently, Martinez Bueno et al. [31] using the same instrument test in our study already assessed its performance for the simultaneous quantitative screening of 10 target pharmaceuticals and the qualitative identification of non-targets after direct water injection. These approaches are at the forefront of a movement from traditional monitoring to environmental forensics applications. Recent examples are the identification of biomarkers as a potential way to disentangle sewage and manure sources [32], to analyze anthropogenic sources [33] or to investigate compositional changes of marine oil spills [34].

Our previous study [4] investigated whether the combined use of LC–QqQ-MS/MS and LC–QTOF- MS is a suitable way in routine performance of systematic pesticide residue determination. Forty-three target pesticides or degradation products were screened by LC–QqQ-MS/MS with limits of detection ranged from 0.04 to 2 ng L−1. The further application of ESI–QTOF-MS using two simultaneous acquisition functions with low and high collision energy (MSE approach) and acquiring the full mass spectra allowed to identify 14 additional compounds against a home-made database (≈1100 organic pollutants) but with no idea on their concentration.

This study goes an step forward into the analytical strategies developed for quantitative and non-quantitative non-target screening of contaminants using a last generation LC–QTOF-MS (ABSciex TripleTOF™ 5600) by ion extraction in front of a database of more than 2000 compounds with accurate mass information and, if available, retention times. An information dependent acquisition (IDA) methods allow to obtain automatically MS/MS spectra of the most intense precursor ions (without previous selection) to additionally confirm the identity of the detected compounds by MS/MS library searching. That means the isolation and further fragmentation of the precursor ion, providing higher confidence in the identification. Furthermore, for the first time and in order to identify relevant unexpected contaminants for the water systems and define changes in the water fingerprints, statistical data analysis using principal component analysis (PCA) and principal components variable grouping (PCVG) was combined with empirical formula calculation, online database (chemspider or other internet databases) searching, and MS/MS fragment ion interpretation to successfully detect unknown contaminants as an insight within environmental forensics. Last but not least, the quantitative capabilities of the system were explored for 42 currently used pesticides, the determination of which was validated according to the European guidelines [35]. The possibility to limit the analysis to one instrument will provide advantages in terms of saving time and cost of the determination.

Section snippets

Reagents

Acetochlor, alachlor, atrazine, deisopropylatrazine, deethylatrazine, azinphos-methyl, buprofezin, carbofuran, 3-hydroxycarbofuran, chlorfenvinphos, chlorpyriphos, diazinon, diuron, fenitrothion, fenthion, fenthion-sulfoxide, fenthion-sulfone, hexythiazox, imazalil, imidacloprid, isoproturon, malathion, methiocarb, prochloraz, pyriproxyfen, simazine, tolclophos-methyl, molinate, omethoate, dimethoate, propazine, propanil, diclofenthion, parathion-methyl, parathion-ethyl, terbutryne,

Searching of water pollutants against libraries

In relation to the chromatographic separation, generic eluents (water–methanol both 10 mM ammonium formate) were used considering that the selected pesticides belong to several families with different chemical properties. All of the compounds were properly eluted using the gradient profile indicated in Section 2.3. The optimized conditions (see Section 2.3) provided reproducible retention times (RTs), which ranged from 0.92 min (omethoate) to 13.17 min (pyriproxyfen) (Table 1). Variations were

Conclusions

The applicability and efficiency of the LC–QqTOF-MS technique in automated IDA-MS/MS for the qualitative and quantitative analysis has been demonstrated by the development of one of the first applications reported of this technique for the simultaneous determination of 43 pesticides and identification of a large number of non-target pesticides and pharmaceutically active compounds in wastewater and river water samples. The method has been demonstrated to be a very simple, fast, and viable

Acknowledgements

This work has been supported by the Spanish Ministry of Economy and Competitiveness through the projects “Assessing and Predicting Effects on Water Quantity and Quality in Iberian Rivers Caused by Global Change (SCARCE)” (No. CSD2009-00065, http://www.scarceconsolider.es) and “Evaluation of Emerging Contaminants in the Turia River Basins: From Basic Research to the Application of Environmental Forensics (EMERFOR)” (GCL2011-29703-C02-02, http://mefturia.es). We also thank to the mass

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