Shifting the paradigm in gas chromatography mass spectrometry pesticide analysis using high resolution accurate mass spectrometry

High resolution mass spectrometry targeted analysis and suspect screening of pesticide residues in fruit samples and assessment of dietary exposure

Fruits consistently hold a prominent position in healthy dietary habits. Pesticides are used to manage plant diseases, achieve sustainable production, and maintain high food standards. This study utilized a comprehensive analytical technique that involved both targeted analysis and suspect screening. Analysis was conducted using Ultra-high-performance liquid chromatography coupled with hybrid Linear Trap Quadrupole (LTQ)/Orbitrap High Resolution Mass Spectrometry (HRMS) to examine pesticide levels in fruits. The matrices chosen comprised fruit commodities that are commonly consumed in Greece, including table grapes, apples, pears, citrus fruits, and strawberries. The QuEChERS approach was effectively validated for 30 specific pesticides. According to the method acceptance criteria established by SANTE, the QuEChERS method have shown exceptional efficiency in extracting the chosen pesticides, with recovery rates ranging from 70% to 120% in three concentration levels (10, 50, 100 μg kg-1). It also exhibited outstanding linearity, with an R2 more than 0.99. The method exhibited exceptional precision, with relative standard deviations (RSDs) below 20%. Additionally, the combined measurement uncertainty (MU%) was found to be acceptable, remaining below 50% The quantification limits were below 10 μg kg-1 for the majority of the analytes, satisfying the Maximum Residue Levels (MRLs) established by the European Commission. Following targeted analysis, a dietary risk assessment was performed, revealing that both acute and chronic hazard quotients (aHQ and cHQ), along with chronic hazard index (cHI) were below 1, which indicated that the studied commodities are safe for human consumption. In addition, a suspect screening workflow was developed based on an in-house database comprising 355 pesticides commonly applied to the relevant commodities and related transformation products (TPs). Overall, through suspect screening, twenty-two additional pesticides and TPs not included in the target list were identified. Hence, this approach is anticipated to function as proactive alert system guaranteeing the long-term viability of agricultural production.

Electrochemical Sensors based on Gold-Silver Core-Shell Nanoparticles Combined with a Graphene/PEDOT:PSS Composite Modified Glassy Carbon Electrode for Paraoxon-ethyl Detection

Herein, a nonenzymatic detection of paraoxon-ethyl was developed by modifying a glassy carbon electrode (GCE) with gold-silver core-shell (Au-Ag) nanoparticles combined with the composite of graphene with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). These core-shell nanoparticles (Au-Ag) were synthesized using a seed-growth method and characterized using UV-vis spectroscopy and high-resolution transmission electron microscopy (HR-TEM) techniques. Meanwhile, the structural properties, surface morphology and topography, and electrochemical characterization of the composite of Au-Ag core-shell/graphene/PEDOT:PSS were analyzed using infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) techniques. Moreover, the proposed sensor for paraoxon-ethyl detection based on Au-Ag core-shell/graphene/PEDOT:PSS modified GCE demonstrates good electrochemical and electroanalytical performance when investigated with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry techniques. It was found that the synergistic effect between Au-Ag core-shell nanoparticles and the composite of graphene/PEDOT:PSS provides a higher conductivity and enhanced electrocatalytic activity for paraoxon-ethyl detection at an optimum pH of 7. At pH 7, the proposed sensor for paraoxon-ethyl detection shows a linear range of concentrations from 0.2 to 100 μM with a limit of detection of 10 nM and high sensitivity of 3.24 μA μM-1 cm-2. In addition, the proposed sensor for paraoxon-ethyl confirmed good reproducibility, with the possibility of being further developed as a disposable electrode. This sensor also displayed good selectivity in the presence of several interfering species such as diazinon, carbaryl, ascorbic acid, glucose, nitrite, sodium bicarbonate, and magnesium sulfate. For practical applications, this proposed sensor was employed for the determination of paraoxon-ethyl in real samples (fruits and vegetables) and showed no significant difference from the standard spectrophotometric technique. In conclusion, this proposed sensor might have a potential to be developed as a platform of electrochemical sensors for pesticide detection.

Wide-Scope Multi-residue analysis of pesticides in beef by gas chromatography coupled with quadrupole Orbitrap mass spectrometry

Increasing pesticide contamination in foods of animal origin has made the wide-scope multi-residue analysis of pesticides an international concern. By using 191 pesticides, this study investigates a sensitive and reliable method for multi-residue analysis of pesticides in beef to determine the extent of the application of this method. The QuEChERS method was employed to extract and purify the pesticides as C18 was utilized as the absorbents. Then, the purified pesticides were analysed using gas chromatography - quadrupole orbitrap mass spectrometry (GC-Q-Orbitrap-MS). The validation test results revealed that this method was satisfactorily sensitive since its screening detection limit (SDL) ranged from 0.2 to 100 µg∙kg^-1. The recovery tests implemented at three spiking levels, namely 100, 200, and 500 µg∙kg^-1, generated the results of 71.95 %-113.97 %, while the intra- and inter-day precisions were 0.27 %-17.94 %, indicating that this method had excellent accuracy and precision.

Unified Method for Target and Non-Target Monitoring of Pesticide Residues in Fruits and Fruit Juices by Gas Chromatography-High Resolution Mass Spectrometry

A new polyvalent wide-scope analytical method, valid for both raw and processed (juices) fruits, combining target and non-target strategies, has been developed and validated to determine low concentrations of 260 pesticides, as well as many potential non-target substances and metabolites. The target approach has been validated according to SANTE Guide requirements. Trueness, precision, linearity, and robustness values were validated in raw fruit (apple) and juice (apple juice) as representative solid and liquid food commodities. Recoveries were between 70-120% and two ranges of linearity were observed: 0.5-20 μg kg^-1 (0.5-20 μg L^-1 apple juice) and 20-100 μg kg^-1 (20-100 μg L^-1 apple juice). The limits of quantification (LOQs) reached were lower than 0.2 μg kg^-1 in apple (0.2 μg L^-1 apple juice) in most cases. The developed method, based on QuEChERS extraction followed by gas chromatography-high resolution mass spectrometry (GC-HRMS), achieves part-per-trillions lower limits, which allowed the detection of 18 pesticides in commercial samples. The non-target approach is based on a retrospective analysis of suspect compounds, which has been optimized to detect up to 25 additional compounds, increasing the scope of the method. This made it possible to confirm the presence of two pesticide metabolites which were not considered in the target screening, phtamlimide and tetrahydrophthalimide.

Current Role of Mass Spectrometry in the Determination of Pesticide Residues in Food

The extensive use of pesticides represents a risk to human health. Consequently, legal frameworks have been established to ensure food safety, including control programs for pesticide residues. In this context, the performance of analytical methods acquires special relevance. Such methods are expected to be able to determine the largest number of compounds at trace concentration levels in complex food matrices, which represents a great analytical challenge. Technical advances in mass spectrometry (MS) have led to the development of more efficient analytical methods for the determination of pesticides. This review provides an overview of current analytical strategies applied in pesticide analysis, with a special focus on MS methods. Current targeted MS methods allow the simultaneous determination of hundreds of pesticides, whereas non-targeted MS methods are now applicable to the identification of pesticide metabolites and transformation products. New trends in pesticide analysis are also presented, including approaches for the simultaneous determination of pesticide residues and other food contaminants (i.e., mega-methods), or the recent application of techniques such as ion mobility–mass spectrometry (IM–MS) for this purpose.

Towards Higher Sensitivity of Mass Spectrometry: A Perspective From the Mass Analyzers

Mass spectrometry (MS) is one of the most widely used analytical techniques in many fields. Recent developments in chemical and biological researches have drawn much attention to the measurement of substances with low abundances in samples. Continuous efforts have been made consequently to further improve the sensitivity of MS. Modifications on the mass analyzers of mass spectrometers offer a direct, universal and practical way to obtain higher sensitivity. This review provides a comprehensive overview of the latest developments in mass analyzers for the improvement of mass spectrometers' sensitivity, including quadrupole, ion trap, time-of-flight (TOF) and Fourier transform ion cyclotron (FT-ICR), as well as different combinations of these mass analyzers. The advantages and limitations of different mass analyzers and their combinations are compared and discussed. This review provides guidance to the selection of suitable mass spectrometers in chemical and biological analytical applications. It is also beneficial to the development of novel mass spectrometers.

Rapid Screening of 350 Pesticide Residues in Vegetable and Fruit Juices by Multi-Plug Filtration Cleanup Method Combined with Gas Chromatography-Electrostatic Field Orbitrap High Resolution Mass Spectrometry

A new method for screening pesticide residues in vegetable and fruit juices by the multi-plug filtration cleanup (m-PFC) method combined with gas chromatography-electrostatic field orbitrap high resolution mass spectrometry(GC-Orbitrap/MS) was developed. The samples were extracted with acetonitrile, purified with m-PFC and determined by GC-Orbitrap/MS. Qualitative analysis was confirmed by retention time, accurate molecular mass and quantitative analysis were performed with the matrix standard calibration. It could eliminate matrix interference effectively. Eight kinds of typical samples (orange juice, apple juice, grape juice, strawberry juice, celery juice, carrot juice, cucumber juice, tomato juice) were evaluated. The linear ranges of the 350 pesticides were from 5 to 500 μg/kg, with good correlation coefficients greater than 0.990. The limits of detection (LODs) were 0.3-3.0 μg/kg and the limits of quantification (LOQs) were 1.0-10.0 μg/kg. The average recoveries at three spiked levels of 10, 100, 200 μg/kg were in the range of 72.8-122.4%, with relative standard deviations (RSDs) of 2.0-10.8%. The method has effectively improved the determination efficiency of pesticide residue screening by high-resolution mass spectrometry in vegetable and fruit juices.

Advances in high resolution GC-MS technology: a focus on the application of GC-Orbitrap-MS in metabolomics and exposomics for FAIR practices

Gas chromatography-mass spectrometry (GC-MS) provides a complementary analytical platform for capturing volatiles, non-polar and (derivatized) polar metabolites and exposures from a diverse array of matrixes. High resolution (HR) GC-MS as a data generation platform can capture data on analytes that are usually not detectable/quantifiable in liquid chromatography mass-spectrometry-based solutions. With the rise of high-resolution accurate mass (HRAM) GC-MS systems such as GC-Orbitrap-MS in the last decade after the time-of-flight (ToF) renaissance, numerous applications have been found in the fields of metabolomics and exposomics. In a short span of time, a multitude of studies have used GC-Orbitrap-MS to generate exciting new high throughput data spanning from diverse basic to applied research areas. The GC-Orbitrap-MS has found application in both targeted and untargeted efforts for capturing metabolomes and exposomes across diverse studies. In this review, I capture and summarize all the reported studies to date, and provide a snapshot of the milieu of commercial and open-source software solutions, spectral libraries, and informatics solutions available to a GC-Orbitrap-MS system instrument user or a data analyst dealing with these datasets. Lastly, but importantly, I provide an account on data sharing and meta-data capturing solutions that are available to make HRAM GC-MS based metabolomics and exposomics studies findable, accessible, interoperable, and reproducible (FAIR). These FAIR practices would allow data generators and users of GC-HRMS instruments to help the community of GC-MS researchers to collaborate and co-develop exciting tools and algorithms in the future.

Comparison of new approach of GC-HRMS (Q-Orbitrap) to GC-MS/MS (triple-quadrupole) in analyzing the pesticide residues and contaminants in complex food matrices

Performances of multiresidue analysis of one hundred of pesticides and contaminants, using GC-Q-Orbitrap method in full scan mode were compared to those obtained with GC-triple-quadrupole method in multiple reaction monitoring mode. In terms of sensitivity, 86% of molecules exhibited lower limit of detection values using GC-Q-Orbitrap than using GC-triple-quadrupole. For the GC-Q-Orbitrap method, more than 85% of the pesticides and contaminants showed good recovery [70-120%] in wheat samples, with relative standard deviation values < 20%. GC-Q-Orbitrap method appeared the most sensitive for most pesticides studied in wheat with limit of quantification values ranged between 0.1 µg/kg and 4 µg/kg. Moreover, the matrix effect was acceptable in wheat extracts for 84 molecules but strong suppression of the chromatographic signal was observed for 16 molecules for the GC-Q-Orbitrap method. The injection of unpurified wheat extracts spiked at 10 µg/kg proved the potential of the GC-Q-Orbitrap method for use in performing high-throughput pesticide screening.

Technical Overview of Orbitrap High Resolution Mass Spectrometry and Its Application to the Detection of Small Molecules in Food (Update Since 2012)

Food safety and quality issues are becoming increasingly important and attract much attention, requiring the development of better analytical platforms. For example, high-resolution (especially Orbitrap) mass spectrometry simultaneously offers versatile functions such as targeted/non-targeted screening while providing qualitative and quantitative information on an almost unlimited number of analytes to facilitate routine analysis and even allows for official surveillance in the food field. This review covers the current state of Orbitrap mass spectrometry (OMS) usage in food analysis based on research reported in 2012-2019, particularly highlighting the technical aspects of OMS application and the achievement of OMS-based screening and quantitative analysis in the food field. The gained insights enhance our understanding of state-of-the-art high-resolution mass spectrometry and highlight the challenges and directions of future research.

Multi-residue analysis of pesticide residues and polychlorinated biphenyls in fruit and vegetables using orbital ion trap high-resolution accurate mass spectrometry

With the increasing demand on pesticide residue laboratories to increase their scope of analysis, high-resolution accurate mass (HRAM) systems have found increasing popularity in this area. The systems have the advantage of much more reliable confirmation as high resolution increases the ability to distinguish between masses which are close together and the mass accuracy achieved limits the number of structural formulae. To date, much of the work involving these systems has revolved around developing screening methods and little has been done on use of these systems for quantitative methods. Here we describe the development and validation of a quantitative method for the analysis of 167 pesticide residues and polychlorinated biphenyls (PCBs) in samples of fruit and vegetables according to the protocol described in EU SANTE guidance document. The determination method involves analysis using a GC QExactive orbitrap in full scan mode using EI. The samples were then extracted using the standard mini-Luke method. After extraction with acetone/dichloromethane/petroleum ether 40-60 °C, a solvent exchange into ethyl acetate is carried out. Recovery work was carried out in cucumber, lemon and broccoli representing high water content, high acid content and high chlorophyll content commodity groups. The results show that the default MRL of 10 ppb can be achieved for more than 93% of the pesticides studied. Mass accuracy, ion ratio and matrix effect studies show that the method is robust and provides a viable alternative to triple quadrupole mass spectrometer systems for the quantification of pesticide residues in fruit and vegetable samples.

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.

Development of a high-throughput screening analysis for 288 drugs and poisons in human blood using Orbitrap technology with gas chromatography-high resolution accurate mass spectrometry

The screening analysis for drugs and poisons always symbolizes the capabilities of a forensic laboratory. Due to the rapid emergence of new compounds in clinical and forensic intoxication cases, sensitive and specific methods are necessary for the screening of wide range of target compounds. A novel high-throughput screening method has been developed for the toxicological analysis of 288 drugs and poisons in human blood using Orbitrap technology with gas chromatography-high resolution mass spectrometry (GC-HRMS). This method allows for the fast detection and identification of high-throughput forensically important drugs and poisons, e.g., drugs of abuse (cocaine, amphetamines, synthetic cannabinoids, opiates, hallucinogen), sedative-hypnotics, antidepressants, non-steroidal anti-inflammatory drugs, pesticides (acaricides, fungicides, insecticides, nematicides), and cardiovascular agents in one single GC-Q Exactive run. After a simple extraction with ethyl ether and buffer, following centrifugation, the supernatant was injected into the system. For detection, spiked blood samples were analyzed by Orbitrap-GC-HRMS using an electrospray ionization in full scan mode with a scan range from 40 to 650 (m/z). The identification of drugs and poisons in the samples was carried out by searching the accurate molecular mass of characteristic fragment ions, ion rations and retention time (RT) against the in-house library that we developed with 70 ev electron energy. The limit of detection (LOD) for most compounds (249 in a total of 288 compounds) was below 100 ng/mL. For selectivity, no substances have been identified in drug-free blood samples from six different sources, and the method was suitable for the recovery and the carryover. The coefficient of variation (CV) of the RTs was below 0.99% in all reproducibility experiments. Mass accuracy was always better than 3 ppm, corresponding to a maximum mass error of 1.04 millimass units (mmu). The developed method was applied to 136 real samples from forensic cases, demonstrating its suitability for the sensitive and fast screening of high-throughput drugs in human blood samples.

Occurrence and distribution of pesticides in precipitation as revealed by targeted screening through GC-MS/MS

Facing the tough challenge of precise measurement of ever-increasing numbers of organic contaminants in the environment, there is an urgent need for more reliable and cost-effective methodologies. In this study, we developed and validated a screening method for analysis of over 450 pesticides in precipitation using gas chromatography with tandem mass spectrometry (GC-MS/MS) in multiple reaction monitoring (MRM) mode. Solid phase extraction (SPE) was applied to extract target analytes from precipitation. Using this targeted approach, we managed to detect 123 pesticides with maximum retention time shifts below 0.1 min (except for DEET) in 101 precipitation samples collected between October 2015 and March 2017 in Singapore. This is probably the first study to report the measurements of a wide range of pesticides in precipitation. A spectrum of insecticides, herbicides, fungicides and their synergists were detected and among them DEET, malathion and carbaryl were the most frequently detected pesticides (detection frequency: 100%, 96% & 67%). The Spearman correlations suggest that some pesticides of different subgroups had significant correlations. It is believed that these finding could shed light on the understanding of the contribution of precipitation to environmental contaminants in water cycle.

High-resolution gas chromatography/mass spectrometry metabolomics of non-human primate serum

RATIONALE

Metabolomics analyses using gas chromatography/mass spectrometry (GC/MS)-based metabolomics are heavily impeded by the lack of high-resolution mass spectrometers and limited spectral libraries to complement the excellent chromatography that GC platforms offer, a challenge that is being addressed with the implementation of high-resolution (HR) platforms such as 1D-GC/Orbitrap-MS.

METHODS

We used serum samples from a non-human primate (NHP), a baboon (Papio hamadryas), with suitable quality controls to quantify the chemical space using an advanced HRMS platform for confident metabolite identification and robust quantification to assess the suitability of the platform for routine clinical metabolomics research. In a complementary approach, we also analyzed the same serum samples using two-dimensional gas chromatography/time-of-flight mass spectrometry (2D-GC/TOF-MS) for metabolite identification and quantification following established standard protocols.

RESULTS

Overall, the 2D-GC/TOF-MS (~5000 peaks per sample) and 1D-GC/Orbitrap-MS (~500 peaks per sample) analyses enabled identification and quantification of a total of 555 annotated metabolites from the NHP serum with a spectral similarity score Rsim  ≥ 900 and signal-to-noise (S/N) ratio of >25. A common set of 30 metabolites with HMDB and KEGG IDs was quantified in the serum samples by both platforms where 2D-GC/TOF-MS enabled quantification of a total 384 metabolites (118 HMDB IDs) and 1D-GC/Orbitrap-MS analysis quantification of a total 200 metabolites (47 HMDB IDs). Thus, roughly 30-70% of the peaks remain unidentified or un-annotated across both platforms.

CONCLUSIONS

Our study provides insights into the benefits and limitations of the use of a higher mass resolution and mass accuracy instrument for untargeted GC/MS-based metabolomics with multi-dimensional chromatography in future studies addressing clinical conditions or exposome studies.

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.