Suspected-target pesticide screening using gas chromatography–quadrupole time-of-flight mass spectrometry with high resolution deconvolution and retention index/mass spectrum library

Identification of AhR agonists in sediments of the Bohai and Yellow Seas using advanced effect-directed analysis and in silico prediction

Novel aryl hydrocarbon receptor (AhR) agonists were identified in coastal sediments in the Yellow and Bohai Seas by use of a combination of effect-directed analysis (EDA) and in silico prediction. A total of 125 sediments were screened for AhR-mediated potencies using H4IIE-luc bioassay. Great potencies were observed in organic extracts, mid-polar fraction (F2), and subfractions of F2 (F2.6-F2.9) of sediments collected from Nantong, Qinhuangdao, and Yancheng. Less than 15% AhR potencies could be explained by detected dioxin-like PAHs. Full-scan screening analysis was conducted for the more potent fractions using GC-QTOFMS to investigate the presence of unmonitored AhR agonists. A five-step prioritization strategy was applied; 92 candidate compounds satisfied all criteria. Among these chemicals, thirteen were evaluated for AhR efficacy. Six compounds; benz[b]anthracene, 6-methylchrysene, 2-methylbenz[a]anthracene, 1-methylbenz[a]anthracene, 1,12-dimethylbenzo[c]phenanthrene, and indeno[1,2,3-cd]fluoranthene, exhibited significant AhR-mediated efficacies. 1,12-dimethylbenzo[c]phenanthrene and indeno[1,2,3-cd]fluoranthene were identified as novel AhR agonists. Potency balance analysis showed that the six newly identified AhR agonists explained 0.4-100% of the total AhR-mediated potencies determined. Overall, combining EDA and in silico prediction applied in this study demonstrated the benefits of assessing the potential toxic effects of previously unidentified AhR agonists in sediments from the coasts of China and Korea.

Development and application of an in-house library and workflow for gas chromatography-electron ionization-accurate-mass/high-resolution mass spectrometry screening of environmental samples

This work presents an optimized gas chromatography–electron ionization–high-resolution mass spectrometry (GC-EI-HRMS) screening method. Different method parameters affecting data processing with the Agilent Unknowns Analysis SureMass deconvolution software were optimized in order to achieve the best compromise between false positives and false negatives. To this end, an accurate-mass library of 26 model compounds was created. Then, five replicates of mussel extracts were spiked with a mixture of these 26 compounds at two concentration levels (10 and 100 ng/g dry weight in mussel, 50 and 500 ng/mL in extract) and injected in the GC-EI-HRMS system. The results of these experiments showed that accurate mass tolerance and pure weight factor (combination of reverse-forward library search) are the most critical factors. The validation of the developed method afforded screening detection limits in the 2.5–5 ng range for passive sampler extracts and 1–2 ng/g for mussel sample extracts, and limits of quantification in the 0.6–3.2 ng and 0.1–1.8 ng/g range, for the same type of samples, respectively, for 17 model analytes. Once the method was optimized, an accurate-mass HRMS library, containing retention indexes, with ca. 355 spectra of derivatized and non-derivatized compounds was generated. This library (freely available at https://doi.org/10.5281/zenodo.5647960), together with a modified Agilent Pesticides Library of over 800 compounds, was applied to the screening of passive samplers, both of polydimethylsiloxane and polar chemical integrative samplers (POCIS), and mussel samples collected in Galicia (NW Spain), where a total of 75 chemicals could be identified.

Non-targeted screening of pyranosides in Rhodiola crenulata using an all ion fragmentation-exact neutral loss strategy combined with liquid chromatography-quadrupole time-of-flight mass spectrometry

INTRODUCTION

Pyranosides as one kind of natural glycosides contain a pyran ring linked to an aglycone in the structure. They occur widely in plants and possess diverse biological activities. The discovery of new pyranosides not only contributes to research on natural products but also may promote pharmaceutical development.

OBJECTIVES

A non-targeted liquid chromatography-quadrupole time-of-flight mass spectrometry method coupled with an all ion fragmentation-exact neutral loss (AIF-ENL) strategy was developed for the screening of pyranosides in plants.

METHODS

Pyranosides in various types were collected as a model. The AIF-ENL strategy comprised three steps: AIF spectrum acquisition and generation, ENL-based searching and identification, and confirmation of structural type using target second-stage mass spectrometry (MS/MS). The strategy was systematically evaluated based on the matrix effects, fragmentation stability, scan rate and screening efficiency and finally applied to Rhodiola crenulata (Hook. f. et Thoms) H. Ohba.

RESULTS

The method was proved to be an efficient tool for the screening of pyranosides. When it was applied to R. crenulata, a total of 24 pyranoside candidates were detected. Among them, six were tentatively identified on the basis of the agreement of their elemental composition with the reported. The other 18 were detected in R. crenulata for the first time.

CONCLUSION

The method offers a new platform for discovering pyranosides. In addition, the developed non-targeted strategy can also be used for other natural products, such as flavonoids and coumarins, as long as there is a common fragmentation behaviour in their MS/MS to generate characteristic neutral losses or fragments.

Assessment of gas chromatography time-of-flight mass spectrometry for the screening of semi-volatile compounds in indoor dust

Indoor dust contains a complex mixture of anthropogenic and synthetic compounds closely related to dermal and respiratory diseases. Target methods have been developed for the quantification of distinct groups of substances in dust samples; however, the comprehensive characterization of the different species existing in this matrix remains a challenging issue. Herein, we assess the performance of gas chromatography (GC) time-of-flight mass spectrometry (TOF-MS), using electron ionization (EI), for the screening of compounds present in indoor dust. Samples are processed by pressurized-liquid extraction (PLE) before GC-EI-TOF-MS analysis. The study proposes a data mining workflow for the non-target identification of species contained in dust extracts, aided by preliminary comparison with nominal resolution EI-MS spectra in the NIST17 library. The possibilities, and the limitations, of the above approach are discussed and the identities of >75 compounds are confirmed by comparison with authentic standards in dust from indoor environments. Some species, such as indigo, phthalic anhydride, 2,4-toluene di-isocyanate, phthalimide, certain UV absorbers and octyl isothiazolinone, identified in this research, have not been previously considered in target methods dealing with dust analysis. The study also evaluates two different algorithms for the suspected-target screening of dust extracts using a customized library of accurate EI-MS spectra. Finally, a semi-quantitative estimation of the range of concentrations for a group of 44 pollutants in a set of 27 dust samples is provided.

Optimization of suspect and non-target analytical methods using GC/TOF for prioritization of emerging contaminants in the Arctic environment

Numerous chemicals have been manufactured through industrial activities and used as consumer products since the late 18th century. Non-target analysis is a new analytical tool to detect many chemicals in environmental samples and to prioritize emerging contaminants. In this study, suspect and non-target analytical methods were optimized using gas chromatography coupled with time-of-flight (GC/TOF) to propose contaminants of emerging concern for the Arctic environment. A suspect analytical method was developed with qualification and qualifier ions, isotopic ratios, and retention times of 215 contaminants including persistent organic pollutants (POPs) to establish an in-house library. Non-target analytical method was also optimized with a deconvoluted ion chromatogram, which is a form that can possibly match the mass spectrum of the NIST library. Multiple environmental samples, such as seawater, air, soil, sediment, sludge, and iceberg, collected from the Arctic region were analyzed with suspect and non-target analysis of GC/TOF after the clean-up procedure with a solid phase extraction (SPE) cartridge. The commonly detected contaminants in the Arctic environmental samples were siloxanes, organophosphate flame retardants, phthalates, synthetic musk compounds, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. Among them, siloxanes and organophosphate flame retardants were proposed to be contaminants of emerging concerns for the Arctic environment. This is the first report to prioritize emerging contaminants in the Arctic environment with suspect and non-target analysis of GC/TOF.

Validating an ion mobility spectrometry-quadrupole time of flight mass spectrometry method for high-throughput pesticide screening

The utility of adding ion mobility (IM) to quadrupole time of flight mass spectrometry (IM-QTOF MS) for highly effective analysis of multiple pesticides in complex matrices was evaluated. Based on an in-house IM-MS database, the identification was performed through the match of the protonated ion ([M + H]+) and the CCS value. Moreover, the structural confirmation was achieved by using the accurate masses of [M + H]+ with its fragment ions, and the reference CCS value. The method did not require chromatographic separation and the analysis time of each measurement cycle is 1.6 min. The "cleaned" IM-MS spectra afforded by the drift time filtration improved the reliability of structural confirmation. As a result, the limit of detection (LOD) of 92% of test pesticides under the APCI mode and 58% of test pesticides under the ESI mode spiked in scallion was not more than 20 ng mL-1. In the analysis of practical samples, the identification of pyrimethanil was confirmed in celery, and benalaxyl and tebuconazole were identified as false positives in scallion. The time-saving, extended-scope and high-throughput method described in this work is capable of determining multiple pesticide residues in complex matrices with high sensitivity for monitoring applications.

Analyzing multiple pesticides in tobacco leaf using gas chromatography with quadrupole time-of-flight mass spectrometry

A method combining gas chromatography with quadrupole time-of-flight mass spectrometry has been developed for the simultaneous analysis of multiple pesticide residues in tobacco leaf. The retention index and high accurate masses of ions from the first-stage and the second-stage mass spectra of each pesticide were collected for qualitation and quantification. A total of 115 pesticides were evaluated. The extract from organic tobacco leaf was used as a model matrix. The limit of detection was <10 ng/mL, and the limit of quantification was in the range of 1-20 ng/mL for 95% of the tested pesticides. The correlation coefficients were >0.9900 for all tested pesticides. At three concentrations (10, 50, and 100 ng/mL), most compounds presented satisfactory recoveries ranging from 70 to 120% and good precision <20%. Finally, three tobacco leaf samples collected from a local market were analyzed. A total of three pesticides were found, including dimethachlon, triadimenol, and flumetralin. Each pesticide was confirmed by the presence of three ions at the expected retention index and mass. In conclusion, gas chromatography with quadrupole time-of-flight mass spectrometry appears to be one of the most efficient tools for the analysis of pesticide residues in tobacco leaf.

Recent applications of gas chromatography with high-resolution mass spectrometry

Gas chromatography coupled to high-resolution mass spectrometry is a powerful analytical method that combines excellent separation power of gas chromatography with improved identification based on an accurate mass measurement. These features designate gas chromatography with high-resolution mass spectrometry as the first choice for identification and structure elucidation of unknown volatile and semi-volatile organic compounds. Gas chromatography with high-resolution mass spectrometry quantitative analyses was previously focused on the determination of dioxins and related compounds using magnetic sector type analyzers, a standing requirement of many international standards. The introduction of a quadrupole high-resolution time-of-flight mass analyzer broadened interest in this method and novel applications were developed, especially for multi-target screening purposes. This review is focused on the development and the most interesting applications of gas chromatography coupled to high-resolution mass spectrometry towards analysis of environmental matrices, biological fluids, and food safety since 2010. The main attention is paid to various approaches and applications of gas chromatography coupled to high-resolution mass spectrometry for non-target screening to identify contaminants and to characterize the chemical composition of environmental, food, and biological samples. The most interesting quantitative applications, where a significant contribution of gas chromatography with high-resolution mass spectrometry over the currently used methods is expected, will be discussed as well.

Thermochemical emission and transformation of chlorinated paraffins in inert and oxidizing atmospheres

Chlorinated paraffins (CPs) generally function as flame retardants and plasticizers in various materials. They are most likely to be processed by thermal processes during the entire life cycle. However, data on the formation and emission of CPs during thermal processes are still not fully understood. In this study, we simulated industrial thermal processes to investigate the emission of medium-chain chlorinated paraffins (MCCPs) and short-chain chlorinated paraffins (SCCPs) using commercial CP52 as the feedstock. We found that CP52 decomposed very easily at 210-320 °C. The decomposition of CPs generated large quantities of MCCPs and SCCPs. These remained in the residue at low temperature (∼200 °C) and were gradually released into the gas phase at higher temperatures. MCCPs and SCCPs were not detected in either the residue or the gas phase when the temperature exceeded 400 °C. However, considerable concentrations of aromatic and chlorinated aromatic hydrocarbons (Cl-PAHs) were identified in the gas phase, and they were formed as the amount of SCCPs and MCCPs decreased. Cl-PAHs were dominated by low-chlorinated chlorobenzenes, polychlorinated biphenyls, and polychlorinated naphthalenes. Oxygen promoted the release and decomposition of SCCPs in the gas phase. The results of the present study revealed the release of MCCPs and SCCPs and their synergistic emission with Cl-PAHs when CPs were subjected to heat. This work may also provide data for developing multiple techniques to control the emission of CPs and Cl-PAHs.

Chromatographic peak reconstruction algorithm to improve qualitative and quantitative analysis of trace pesticide residues

RATIONALE

In order to improve analysis of analytes in trace amounts in a complex matrix, we developed a novel post-processing method, named Chromatographic Peak Reconstruction (CPR), to process the recorded data from gas chromatography/time-of-flight mass spectrometry (GC/TOFMS).

METHODS

For a trace ion, the relative deviation (δ) between the adjacent scanned mass-to-charge ratios (m/z) was found to be inversely proportional to its MS peak intensity. Based on this relationship, the thresholds of δ value within the specified intensity segments were estimated by the CPR and used to screen out the suspicious scan-points in the extracted ion chromatographic (EIC) peak. Then, the intensities of these suspicious scan-points were calibrated to reconstruct a new EIC peak.

RESULTS

In the qualitative analysis of 118 pesticides, 107 out of the test pesticides can be confirmed. The corrected response ratios of the qualitative ion (q) over the quantitative ion (Q), q/Q, became closer to their references. In the quantitative analysis of 10 test pesticides at 5 ppb, the relative errors of the calculated concentrations after using the CPR were below ±1.55%, down from ±2.29% without using the CPR.

CONCLUSIONS

The developed CPR showed great potential in the analysis of trace analytes in complex matrices. It was proved to be a helpful data processing method for the monitoring of trace pesticide residues. Copyright © 2016 John Wiley & Sons, Ltd.

Negative chemical ionization gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry and automated accurate mass data processing for determination of pesticides in fruit and vegetables

Gas chromatography coupled to high resolution hybrid quadrupole time-of-flight mass spectrometry (GC-QTOF MS), operating in negative chemical ionization (NCI) mode and combining full scan with MSMS experiments using accurate mass analysis, has been explored for the automated determination of pesticide residues in fruit and vegetables. Seventy compounds were included in this approach where 50 % of them are not approved by the EU legislation. A global 76 % of the analytes could be identified at 1 μg kg(-1). Recovery studies were developed at three concentration levels (1, 5, and 10 μg kg(-1)). Seventy-seven percent of the detected pesticides at the lowest level yielded recoveries within the 70 %-120 % range, whereas 94 % could be quantified at 5 μg kg(-1), and the 100 % were determined at 10 μg kg(-1). Good repeatability, expressed as relative standard deviation (RSD <20 %), was obtained for all compounds. The main drawback of the method was the limited dynamic range that was observed for some analytes that can be overcome either diluting the sample or lowering the injection volume. A home-made database was developed and applied to an automatic accurate mass data processing. Measured mass accuracies of the generated ions were mainly less than 5 ppm for at least one diagnostic ion. When only one ion was obtained in the single-stage NCI-MS, a representative product ion from MSMS experiments was used as identification criterion. A total of 30 real samples were analyzed and 67 % of the samples were positive for 12 different pesticides in the range 1.0-1321.3 μg kg(-1).

Assessment of gas chromatography time-of-flight accurate mass spectrometry for identification of volatile and semi-volatile compounds in honey

The performance of gas chromatography (GC) combined with a hybrid quadrupole time-of-flight (QTOF) mass spectrometry (MS) system for the determination of volatile and semi-volatile compounds in honey samples is evaluated. After headspace (HS) solid-phase microextraction (SPME) of samples, the accurate mass capabilities of the above system were evaluated for compounds identification. Accurate scan electron impact (EI) MS spectra allowed discriminating compounds displaying the same nominal masses, but having different empirical formulae. Moreover, the use of a mass window with a width of 0.005 Da provided highly specific chromatograms for selected ions, avoiding the contribution of interferences to their peak areas. Additional information derived from positive chemical ionization (PCI) MS spectra and ion product scan MS/MS spectra permitted confirming the identity of novel compounds. The above possibilities are illustrated with examples of honey aroma compounds, belonging to different chemical classes and containing different elements in their molecules. Examples of compounds whose structures could not be described are also provided. Overall, 84 compounds, from a total of 89 species, could be identified in 19 honey samples from 3 different geographic areas in the world. The suitability of responses measured for selected ions, corresponding to above species, for authentication purposes is assessed through principal components analysis.