Global and selective detection of organohalogens in environmental samples by comprehensive two-dimensional gas chromatography–tandem mass spectrometry and high-resolution time-of-flight mass spectrometry

Screening Disinfection Byproducts in Arid-Coastal Wastewater: A Workflow Using GC×GC-TOFMS, Passive Sampling, and NMF Deconvolution Algorithm

Disinfection during tertiary municipal wastewater treatment is a necessary step to control the spread of pathogens; unfortunately, it also gives rise to numerous disinfection byproducts (DBPs), only a few of which are regulated because of the analytical challenges associated with the vast number of potential DBPs. This study utilized polydimethylsiloxane (PDMS) passive samplers, comprehensive two-dimensional gas chromatography (GC×GC) coupled with time-of-flight mass spectrometry (TOFMS), and non-negative matrix factorization (NMF) spectral deconvolution for suspect screening of DBPs in treated wastewater. PDMS samplers were deployed upstream and downstream of the chlorination unit in a municipal wastewater treatment plant located in Abu Dhabi, and their extracts were analyzed using GC×GC-TOFMS. A workflow incorporating a multi-tiered, eight-filter screening process was developed, which successfully enabled the reliable isolation of 22 candidate DBPs from thousands of peaks. The NMF spectral deconvolution improved the match factor score of unknown mass spectra to the reference mass spectra available in the NIST library by 17% and facilitated the identification of seven additional DBPs. The close match of the first-dimension retention index data and the GC×GC elution patterns of DBPs, both predicted using the Abraham solvation model, with their respective experimental counterparts-with the measured data available in the NIST WebBook and the GC×GC elution patterns being those observed for the candidate peaks-significantly enhanced the accuracy of peak assignment. Isotopic pattern analysis revealed a close correspondence for 11 DBPs with clearly visible isotopologues in reference spectra, thereby further strengthening the confidence in the peak assignment of these DBPs. Brominated analogues were prevalent among the detected DBPs, possibly due to seawater intrusion. The fate, behavior, persistence, and toxicity of tentatively identified DBPs were assessed using EPI Suite™ and the CompTox Chemicals Dashboard. This revealed their significant toxicity to aquatic organisms, including developmental, mutagenic, and endocrine-disrupting effects in certain DBPs. Some DBPs also showed activity in various CompTox bioassays, implicating them in adverse molecular pathways. Additionally, 11 DBPs demonstrated high environmental persistence and resistance to biodegradation. This combined approach offers a powerful tool for future research and environmental monitoring, enabling accurate identification and assessment of DBPs and their potential risks.

Comprehensive Two-Dimensional Gas Chromatography as a Bioanalytical Platform for Drug Discovery and Analysis

Over the last decades, comprehensive two-dimensional gas chromatography (GC×GC) has emerged as a significant separation tool for high-resolution analysis of disease-associated metabolites and pharmaceutically relevant molecules. This review highlights recent advances of GC×GC with different detection modalities for drug discovery and analysis, which ideally improve the screening and identification of disease biomarkers, as well as monitoring of therapeutic responses to treatment in complex biological matrixes. Selected recent GC×GC applications that focus on such biomarkers and metabolite profiling of the effects of drug administration are covered. In particular, the technical overview of recent GC×GC implementation with hyphenation to the key mass spectrometry (MS) technologies that provide the benefit of enhanced separation dimension analysis with MS domain differentiation is discussed. We conclude by highlighting the challenges in GC×GC for drug discovery and development with perspectives on future trends.

Comprehensive screening of polybromochlorodibenzo-p-dioxins, dibenzofurans as mixed halogenated compounds in wastewater samples from industrial facilities by GC×GC/ToFMS and post-data processing

An enormous number of pollutants must be investigated to be able to understand which types threaten human health and environmental biota. In this study, we propose a workflow for screening polybromochlorodibenzo-p-dioxins and dibenzofurans (PBCDD/Fs), which are compounds that have thousands of isomers and congeners, by combining measurement of a sample without any in-laboratory-cleanup with the results of comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry and post-data processing. This process can be regarded as "in silico sample cleanup." The post-data processing stage comprises two methods in which the extracted mass spectra are matched to exact mass and isotopic ratios specified as formulae and filtering via mass deficiency. We applied this workflow to wastewater samples from industrial facilities to identify mixtures of halogenated dioxins. As a result, it was estimated that dioxins in an absolute quantity of 10-500 pg could be detected with sufficient accuracy by recovery testing of a standard mixture against sample crude extracts. Tri- to octa-halogenated dioxins were detected in 8 of 13 samples. Leachate from an industrial landfill was found to contain relatively large numbers of PBCDD/Fs, and several congeners were found in wastewater from an industrial fabric facility that handles decabromodiphenyl ether. The workflow, including the post-data processing method developed and applied in this study, has the advantage that additional identifications can be performed at any time from a single set of measurement data. This also enables the screening of substances that have thousands of homologous isomers, such as chlorinated and brominated dioxins, as well as other non-halogenated compounds.

Automated Screening and Filtering Scripts for GC×GC-TOFMS Metabolomics Data

Comprehensive two-dimensional gas chromatography mass spectrometry (GC×GC-MS) is a powerful tool for the analysis of complex mixtures, and it is ideally suited to discovery studies where the entire sample is potentially of interest. Unfortunately, when unit mass resolution mass spectrometers are used, many detected compounds have spectra that do not match well with libraries. This could be due to the compound not being in the library, or the compound having a weak/nonexistent molecular ion cluster. While high-speed, high-resolution mass spectrometers, or ion sources with softer ionization than 70 eV electron impact (EI) may help with some of this, many GC×GC systems presently in use employ low-resolution mass spectrometers and 70 eV EI ionization. Scripting tools that apply filters to GC×GC-TOFMS data based on logical operations applied to spectral and/or retention data have been used previously for environmental and petroleum samples. This approach rapidly filters GC×GC-TOFMS peak tables (or raw data) and is available in software from multiple vendors. In this work, we present a series of scripts that have been developed to rapidly classify major groups of compounds that are of relevance to metabolomics studies including: fatty acid methyl esters, free fatty acids, aldehydes, alcohols, ketones, amino acids, and carbohydrates.

Automating and Extending Comprehensive Two-Dimensional Gas Chromatography Data Processing by Interfacing Open-Source and Commercial Software

Comprehensive two-dimensional gas chromatography (GC×GC) is a powerful analytical tool for both nontargeted and targeted analyses. However, there is a need for more integrated workflows for processing and managing the resultant high-complexity datasets. End-to-end workflows for processing GC×GC data are challenging and often require multiple tools or software to process a single dataset. We describe a new approach, which uses an existing underutilized interface within commercial software to integrate free and open-source/external scripts and tools, tailoring the workflow to the needs of the individual researcher within a single software environment. To demonstrate the concept, the interface was successfully used to complete a first-pass alignment on a large-scale GC×GC metabolomics dataset. The analysis was performed by interfacing bespoke and published external algorithms within a commercial software environment to automatically correct the variation in retention times captured by a routine reference standard. Variation in ¹t_R and ²t_R was reduced on average from 8 and 16% CV prealignment to less than 1 and 2% post alignment, respectively. The interface enables automation and creation of new functions and increases the interconnectivity between chemometric tools, providing a window for integrating data-processing software with larger informatics-based data management platforms.

The pollution profiles and human exposure risks of chlorinated and brominated PAHs in indoor dusts from e-waste dismantling workshops: Comparison of GC-MS, GC-MS/MS and GC × GC-MS/MS determination methods

The toxicities of some chlorinated and brominated polycyclic aromatic hydrocarbons (X-PAHs) are higher than their corresponding parent PAHs. However, the identification and quantitation of X-PAHs in environment are still changeable and limitedly reported. To develop a robust method for routine analysis of X-PAHs in environmental samples, the determination of 34 X-PAHs was performed and compared using different instruments, including gas chromatography-mass spectrometry (GC-MS), gas chromatography-tandem mass spectrometry (GC-MS/MS) in both electron ionization (EI) and negative chemical ionization (NCI) modes, and comprehensive two-dimensional gas chromatograph-tandem mass spectrometer (GC × GC-MS/MS). GC-EI-MS/MS possessed the highest sensitivity with method detection limits of 2.00-40.0 and 2.00-20.0 pg/g dry weight (dw) for Cl-PAHs and Br-PAHs, respectively. This validated method was then applied to analyze X-PAHs in indoor dusts from a typical e-waste dismantling workshop, and the concentrations of Σ₁₈Br-PAHs (8.80-399 ng/g dw) were higher than Σ₁₆Cl-PAHs (7.91-137 ng/g dw). The toxicity equivalency quantities (TEQs) of Cl-PAHs at e-waste dismantling workshop and Br-PAHs at raw materials crushing workshop showed the highest values of 176 and 453 pg·TEQ/g, respectively. Cl-PAHs and Br-PAHs posed a potential health risk to workers through dust ingestion in workshops. Further attention should be payed to the formation mechanism of X-PAHs and the health risk.

Ascertaining Hydrogen-Abstraction Reaction Efficiencies of Halogenated Organic Compounds in Electron Impact Ionization Processes by Gas Chromatography-High-Resolution Mass Spectrometry

H-Abstraction reactions occurring during electron impact ionization processes in electron ionization mass spectrometry (EI-MS) are a long-standing and crucial topic in MS research. Yet, some critical relevant mechanisms are controversial and ambiguous, and information about the EI-induced H-abstraction reactions of halogenated organic compounds (HOCs) is completely in the dark. This study provides a systematic investigation of H-abstraction reactions of HOCs taking place in the EI source using ¹³C₆-hexachlorobenzene (¹³C₆-HCB) and ¹³C₆-hexabromobenzene (¹³C₆-HBB) as exemplary compounds by gas chromatography (GC)-high-resolution mass spectrometry (GC-HRMS). The H-abstraction efficiencies were evaluated with the MS signal intensity ratios of ions with H-abstraction relative to the corresponding original ions (without H-abstraction). Ion source temperatures, EI energies, and numbers of heavy isotope atoms (³⁷Cl or ⁸¹Br) of isotopologues were investigated in terms of their effects on the H-abstraction efficiencies. The H-abstraction efficiencies of individual isotopologues generally decreased from the first to the last isotopologues of respective ions, and those of individual ions were different from each other, with the highest values of 0.017 and 0.444 for ¹³C₆-HCB and ¹³C₆-HBB, respectively. The overall H-abstraction efficiencies involving all measured ions of ¹³C₆-HCB and ¹³C₆-HBB were 0.004 and 0.128, respectively. With increasing ion source temperatures, the H-abstraction efficiencies first increased to a summit and then began to linearly decrease. EI energies and emission currents could impact the H-abstraction efficiencies but showed no certain tendency. The H-abstraction reactions were inferred to belong to ion-molecule reactions, and the siloxanes bleeding from the GC column might be a hydrogen source. Some strategies were proposed for eliminating or alleviating the interference triggered by the H-abstraction reactions in EI-MS in identification of halogenated organic pollutants (HOPs). Our findings provide a better understanding of the EI-induced H-abstraction reactions of HOCs and may benefit the identification of HOPs in environmental analysis, especially for novel HOPs.

Quantitative and semiquantitative analyses of hexa-mix-chlorinated/brominated benzenes in fly ash, soil and air using gas chromatography-high resolution mass spectrometry assisted with isotopologue distribution computation

Hexa-mix-chlorinated/brominated benzenes (HXBs), a group of newly found analogues of hexachlorobenzene (HCB) and hexabromobenzene (HBB), may exhibit similar environmental risks and toxicities as HCB and HBB, and therefore possess high interests in environmental and toxicological research. Yet information regarding HXBs in the environment remains scarce. In this study, we developed an isotope dilution method for quantitative and semiquantitative determination of five HXBs in fly ash, soil and air using gas chromatography high resolution mass spectrometry (GC-HRMS) in multiple ion detection mode. The samples were Soxhlet-extracted and purified with multilayer composite silica gel-alumina columns, followed by GC-HRMS detection. Identification of HXBs was conducted by the comparison between theoretical and detected mass spectra using paired-samples T test and cosine similarity analysis. Two HXBs (C₆BrCl₅ and C₆Br₄Cl₂) with reference standards were quantitatively determined while the rest three (C₆Br₂Cl₄, C₆Br₃Cl₃ and C₆Br₅Cl) without reference standards were semiquantitatively analyzed by sharing the calibration curves of C₆BrCl₅ and C₆Br₄Cl₂ in cooperation with isotopologue distribution computation. The accuracies for C₆BrCl₅ and C₆Br₄Cl₂ were 87.3-107.8% with relative standard deviations (RSD) of 2.8-5.0%. The method limits of quantification of the HXBs were 0.10 ng/g in fly ash and soil samples and 0.09 pg/m³ in ambient air samples. The recoveries ranged from 42.7% to 102.1% with RSD of 3.7-13.9%. This method has been successfully applied to the analysis of the HXBs in the environmental samples. The total concentrations of HXBs in the fly ash, soil and ambient air samples were 19.48 ng/g, 10.44 ng/g and 5.13 pg/m³, respectively, which accounted for 10.6%, 0.4% and 10.8% of the corresponding total concentrations of HCB and HBB. This study provides a reference method for quantitative and/or semiquantitative analyses of novel mix-halogenated organic compounds, and sheds light on the full picture of HXBs pollution in the environment.

Biodegradation of the aromatic fraction from petroleum diesel fuel by Oerskovia sp. followed by comprehensive GC×GC-TOF MS

Polycyclic aromatic hydrocarbons (PAHs) from petroleum and fossil fuels are one of the most dominant pollutants in the environment. Since aromatic fraction from petroleum diesel fuel is mainly composed of PAHs, it is important to discover new microorganisms that can biodegrade these compounds. This article describes the biodegradation of the aromatic fraction separated from petroleum diesel fuel using the strain Oerskovia sp. CHP-ZH25 isolated from petroleum oil-contaminated soil. The biodegradation was monitored by gravimetry and GC × GC-TOF MS. An innovative method was applied to visualize degraded compounds in the data provided by a GC × GC-TOF MS. It was shown that Oerskovia sp. CHP-ZH25 degraded 77.4% based on gravimetric analysis within 30 days. Average rate of degradation was 14.4 mg/L/day, 10.5 mg/l/day and 4.0 mg/l/day from 0 to 10 day, 10-20 and 20-30 day, respectively. The order of PAH degradation based on decrease in peak volume after 30 days of incubation was as follows: dibenzothiophene derivatives > benzo[b]thiophene derivatives > naphthalene derivatives > acenaphthene derivatives > acenaphthylene/biphenyl derivatives > fluorene derivatives > phenanthrene/anthracene derivatives. Here we demonstrated that Oerskovia sp. CHP-ZH25 could potentially be a suitable candidate for use in bioremediation of environments polluted with different PAHs.

Selective and comprehensive analysis of organohalogen compounds by GC × GC-HRTofMS and MS/MS

Thousands of organohalogen compounds, including hazardous chemicals such as polychlorinated biphenyls (PCBs) and other persistent organic pollutants (POPs), were selectively and simultaneously detected and identified with simple, or no, purification from environmental sample extracts by using several advanced methods. The methods used were software extraction from two-dimensional gas chromatography-high-resolution time-of-flight mass spectrometry (GC × GC-HRTofMS) data, measurement by negative chemical ionization with HRTofMS, and neutral loss scanning (NLS) with GC × GC-MS/MS. Global and selective detection of organochlorines and bromines in environmental samples such as sediments and fly ash was achieved by NLS using GC × GC-MS/MS (QQQ), with the expected losses of ³⁵Cl and ⁷⁹Br. We confirmed that negative chemical ionization was effective for sensitive and selective ionization of organohalogens, even using GC × GC-HRTofMS. The 2D total ion chromatograms obtained by using negative chemical ionization and selective extraction of organohalogens using original software from data measured by electron impact ionization were very similar; the software thus functioned well to extract organohalogens. Combining measurements made by using these different methods will help to detect organohalogens selectively and globally. However, to compare the data obtained by individual measurements, the retention times of the peaks on the 2D chromatograms need to match.

Comprehensive two-dimensional gas chromatography-mass spectrometry: Recent evolution and current trends

The present contribution is focused on the evolution and current trends of comprehensive two-dimensional gas chromatography-mass spectrometry (GC × GC-MS), with respect to a review that described this specific methodology published at the beginning of 2008 (Mondello et al., 2008). In fact, since then there has been considerable evolution in the MS field, certainly exceeding that observed in GC × GC. In particular, the present paper will cover the combination of novel MS machines [single quadrupole (Q) and triple quadrupole, isotope ratio, low- and high-resolution time-of-flight (ToF), hybrid (Q-ToF)] to GC × GC systems, and will position comprehensive two-dimensional gas chromatography within the wider context of separation science. © 2014 Wiley Periodicals, Inc. Mass Spec Rev 35:524-534, 2016.

Global spectral deconvolution based on non-negative matrix factorization in GC × GC-HRTOFMS

A global spectral deconvolution, based on non-negative matrix factorization (NMF) in comprehensive two-dimensional gas chromatography high-resolution time-of-flight mass spectrometry, was developed. We evaluated the ability of various instrumental parameters and NMF settings to derive high-performance detection in nontarget screening using a sediment sample. To evaluate the performance of the process, a NIST library search was used to identify the deconvoluted spectra. Differences of the instrumental scan rates (25 and 50 Hz) in deconvolution were evaluated and results show that a high scan rate enhanced the number of compounds detected in the sediment sample. A higher mass resolution in the range of 1,000 to 10,000 and a higher m/z precision in the deconvolution were needed to obtain an accurate mass database. After removal of multiple duplicate hits, which occurred in batch processes of NIST library search on the deconvolution result, 62 unique assignable spectra with a match factor ≥900 were obtained in the deconvoluted chromatogram from the sediment sample, including 54 spectra that were refined by the deconvolution. This method will help to detect and build up well-resolved reference spectra from various complex mixtures and will accelerate nontarget screening.

Complementary nontargeted and targeted mass spectrometry techniques to determine bioaccumulation of halogenated contaminants in freshwater species

Assessing the toxicological significance of complex environmental mixtures is challenging due to the large number of unidentified contaminants. Nontargeted analytical techniques may serve to identify bioaccumulative contaminants within complex contaminant mixtures without the use of analytical standards. This study exposed three freshwater organisms (Lumbriculus variegatus, Hexagenia spp., and Pimephales promelas) to a highly contaminated soil collected from a recycling plant fire site. Biota extracts were analyzed by Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) and mass defect filtering to identify bioaccumulative halogenated contaminants. Specific bioaccumulative isomers were identified by comprehensive two-dimensional gas chromatography high-resolution time-of-flight mass spectrometry (GCxGC-HRToF). Targeted analysis of mixed brominated/chlorinated dibenzo-p-dioxins and dibenzofurans (PXDD/PXDFs, X = Br and Cl) was performed by atmospheric pressure gas chromatography tandem mass spectrometry (APGC-MS/MS). Relative sediment and biota instrument responses were used to estimate biota-sediment accumulation factors (BSAFs). Bioaccumulating contaminants varied among species and included polychlorinated naphthalenes (PCNs), polychlorinated dibenzofurans (PCDFs), chlorinated and mixed brominated/chlorinated anthracenes/phenanthrenes, and pyrenes/fluoranthenes (Cl-PAHs and X-PAHs, X = Br and Cl), as well as PXDD/PXDFs. Bioaccumulation potential among isomers also varied. This study demonstrates how complementary high-resolution mass spectrometry techniques identify persistent and bioaccumulative contaminants (and specific isomers) of environmental concern.

Identification of the halogenated compounds resulting from the 1997 Plastimet Inc. fire in Hamilton, Ontario, using comprehensive two-dimensional gas chromatography and (ultra)high resolution mass spectrometry

Between July 9-12, 1997, at least 400 tonnes of polyvinyl chloride (PVC) were consumed in a fire at the Plastimet Inc. plastics recycling facility in Hamilton, Ontario, Canada. This led to the release of contaminants, including highly toxic polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF). This study re-examines a composite soil sample collected shortly after the fire using state-of-the-art FT-ICR (Fourier transform ion cyclotron resonance) and GC × GC-TOF (comprehensive two-dimensional gas chromatography-time-of-flight) mass spectrometry. The FT-ICR experiments led to the identification of approximately 150 molecular formulas, corresponding to chlorinated and mixed chloro/bromo compounds. The majority of these are halogenated polycyclic aromatic hydrocarbons (halo-PAHs), including highly substituted (e.g., C14HCl9 and C16HCl9) and high molecular weight (e.g., C28H12Cl4) Cl-PAHs that have not been reported previously in environmental samples. Complementary GC × GC-TOF experiments resolved individual halo-PAHs, some of which were confirmed with available standards. The concentrations of the most abundant halo-PAH groups, C14H8Cl2 (22 μg/g) and C16H8Cl2 (20 μg/g) are much higher than reported dioxin values and comparable to the corresponding PAH groups C14H10 (12 μg/g) and C16H10 (19 μg/g). The high abundance of the halo-PAHs identified in this study highlights the need for further investigation into their environmental occurrence and risk.

Identification of potential novel bioaccumulative and persistent chemicals in sediments from Ontario (Canada) using scripting approaches with GC×GC-TOF MS analysis

This work describes a single and fast approach using a filtering script as a means of prioritizing sample processing of data acquired by GC×GC-TOF MS for the identification of potentially novel persistent and bioaccumulative halogenated chemicals. The proposed script is based on the recognition of a generic halogenated isotope cluster pattern that allows for the simultaneous detection of chlorinated, brominated, or mixed halogen-substituted compounds in a single classification. Once developed, the script was applied to the identification of organohalogens in stream sediments collected across the southern region of Ontario (Canada). Classified peaks were first compared with available analytical standards and reference libraries to confirm the known chemicals. Unknown potential persistent organic pollutants (POPs) were evaluated for occurrence within the samples and high resolution mass spectrometry was used in order to identify some of the most prevalent compounds in the samples and resulting in the identification of three decachlorinated dechlorane analogs (C18H14Cl10), two undecachlorinated dechlorane species (C18H13Cl11), and a novel mixed chloro/bromo-carbazole (C12H5NCl2Br2) in a number of sediments analyzed. Relative peak abundances of these unknown halogenated compounds were in the same order of magnitude or slightly higher than levels observed for conventional POPs detected in the samples.

Mapping environmental partitioning properties of nonpolar complex mixtures by use of GC × GC

Comprehensive two-dimensional gas chromatography (GC × GC) is effective for separating and quantifying nonpolar organic chemicals in complex mixtures. Here we present a model to estimate 11 environmental partitioning properties for nonpolar analytes based on GC × GC chromatogram retention time information. The considered partitioning properties span several phases including pure liquid, air, water, octanol, hexadecane, particle natural organic matter, dissolved organic matter, and organism lipids. The model training set and test sets are based on a literature compilation of 648 individual experimental partitioning property data. For a test set of 50 nonpolar environmental contaminants, predicted partition coefficients exhibit root-mean-squared errors ranging from 0.19 to 0.48 log unit, outperforming Abraham-type solvation models for the same chemical set. The approach is applicable to nonpolar organic chemicals containing C, H, F, Cl, Br, and I, having boiling points ≤402 °C. The presented model is calibrated, easy to apply, and requires the user only to identify a small set of known analytes that adapt the model to the GC × GC instrument program. The analyst can thus map partitioning property estimates onto GC × GC chromatograms of complex mixtures. For example, analyzed nonpolar chemicals can be screened for long-range transport potential, aquatic bioaccumulation potential, arctic contamination potential, and other characteristic partitioning behaviors.

Environmental mass spectrometry

Environmental mass spectrometry is an important branch of science because it provides many of the data that underlie policy decisions that can directly influence the health of people and ecosystems. Environmental mass spectrometry is currently undergoing rapid development. Among the most relevant directions are a significant broadening of the lists of formally targeted compounds; a parallel interest in nontarget chemicals; an increase in the reliability of analyses involving accurate mass measurements, tandem mass spectrometry, and isotopically labeled standards; and a shift toward faster high-throughput analysis, with minimal sample preparation, involving various approaches, including ambient ionization techniques and miniature instruments. A real revolution in analytical chemistry could be triggered with the appearance of robust, simple, and sensitive portable mass spectrometers that can utilize ambient ionization techniques. If the cost of such instruments is reduced to a reasonable level, mass spectrometers could become valuable household devices.

Untargeted and targeted comprehensive two-dimensional GC analysis using a novel unified high-speed triple quadrupole mass spectrometer

The present manuscript is focused on the evaluation of a novel high-speed triple quadrupole mass spectrometer (QqQ MS), carried out under extreme GC conditions, namely those generated by a flow-modulated (FM) comprehensive two-dimensional GC (GC×GC) system. The novel QqQ MS system is capable of operation under high speed conditions, in both full-scan (maximum scan speed: 20,000 amu/s) and multiple reaction monitoring (MRM) modes. Moreover, the QqQ MS instrument can generate simultaneous full scan/MRM data, also in a very rapid manner. An FM GC × GC-MSMS method was developed for the simultaneous full-scan qualitative analysis of untargeted essential oil compounds, and MRM quali/quantitative analysis of targeted ones, namely three preservatives [o-phenylphenol (OPP), butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA)]. The QqQMS system generated a sufficient number of data points per peak, for both qualitative and quantitative purposes. The degree of sensitivity, reached through the MRM analysis, widely exceeded current-day regulations. Method validation, related to the MRM analysis, was performed considering retention time, peak area and ion ratio repeatability, limits of detection and quantification, and accuracy. Additionally, a spearmint essential oil was spiked with 5 phytosanitary compounds at the 1 ppb level, and analysed through an MRM-only GC × GC-MSMS application. Emphasis was devoted not only on sensitivity (satisfactory for all the contaminants), but also on the importance of precursor ion selection, and of the GC × GC separation process. Finally, sensitivity was compared between the MRM and SIM modes, in scan/MRM, MRM, scan/SIM and SIM analyses, performed on a mixture of 22 phytosanitary products, at a concentration level in the 50-150 ppb range.