Identification and quantification of flavor compounds in smoked tuna fish based on GC-Orbitrap volatolomics approach.

Cold smoking enhances the appeal of fish products, offering consumers a smooth texture and a delicate smoky flavor. This study aims to explore variations in the volatile profile from different exposure times during cold smoking processing (light, moderate, and full-cure) in tune samples. An innovative untargeted analytical approach, headspace solid-phase microextraction combined with gas chromatography and a hybrid quadrupole-orbitrap mass analyzer, was employed to identify 86 volatiles associated with the cold smoking process. Most of these compounds, including phenols, furan derivates, aldehydes, cyclic ketones, and different aromatic species, were found to contribute to the smoke odor. The development of a QuEChERS-based extraction and clean-up method facilitated the quantification of 25 relevant smoky markers across all smoking degrees, revealing significant concentration differences after 15 h of smoking. This research sheds light on the dynamics of cold smoking impact and its on the flavor profile and safety quality of processed fish products.

A comprehensive study on diesel oil bioremediation under microcosm conditions using a combined microbiological, enzymatic, mass spectrometry, and metabarcoding approach.

This study aims at the application of a marine fungal consortium (Aspergillus sclerotiorum CRM 348 and Cryptococcus laurentii CRM 707) for the bioremediation of diesel oil-contaminated soil under microcosm conditions. The impact of biostimulation (BS) and/or bioaugmentation (BA) treatments on diesel-oil biodegradation, soil quality, and the structure of the microbial community were studied. The use of the fungal consortium together with nutrients (BA/BS) resulted in a TPH (Total Petroleum Hydrocarbon) degradation 42% higher than that obtained by natural attenuation (NA) within 120 days. For the same period, a 72 to 92% removal of short-chain alkanes (C12 to C19) was obtained by BA/BS, while only 3 to 65% removal was achieved by NA. BA/BS also showed high degradation efficiency of long-chain alkanes (C20 to C24) at 120 days, reaching 90 and 92% of degradation of icosane and heneicosane, respectively. In contrast, an increase in the levels of cyclosiloxanes (characterized as bacterial bioemulsifiers and biosurfactants) was observed in the soil treated by the consortium. Conversely, the NA presented a maximum of 37% of degradation of these alkane fractions. The 5-ringed PAH benzo(a)pyrene, was removed significantly better with the BA/BS treatment than with the NA (48 vs. 38 % of biodegradation, respectively). Metabarcoding analysis revealed that BA/BS caused a decrease in the soil microbial diversity with a concomitant increase in the abundance of specific microbial groups, including hydrocarbon-degrading (bacteria and fungi) and also an enhancement in soil microbial activity. Our results highlight the great potential of this consortium for soil treatment after diesel spills, as well as the relevance of the massive sequencing, enzymatic, microbiological and GC-HRMS analyses for a better understanding of diesel bioremediation.

Ecological risk assessment of pesticides in the Mijares River (eastern Spain) impacted by citrus production using wide-scope screening and target quantitative analysis.

The widespread use of pesticides, especially in agricultural areas, makes necessary to control their presence in surrounding surface waters. The current study was designed to investigate the occurrence and ecological risks of pesticides and their transformation products in a Mediterranean river basin impacted by citrus agricultural production. Nineteen sites were monitored in three campaigns distributed over three different seasons. After a qualitative screening, 24 compounds was selected for subsequent quantitative analysis. As expected, the lower section of the river was most contaminated, with total concentration >5 µg/L in two sites near to the discharge area of wastewater treatment plants. The highest concentrations were found in September, after agricultural applications and when the river flow is reduced. Ecological risks were calculated using two mixture toxicity approaches (Toxic Unit and multi-substance Potentially Affected Fraction), which revealed high acute and chronic risks of imidacloprid to invertebrates, moderate-to-high risks of diuron, simazine and 2,4-D for primary producers, and moderate-to-high risks of thiabendazole for invertebrates and fish. This study shows that intensive agricultural production and the discharge of wastewater effluents containing pesticide residues from post-harvest citrus processing plants are threatening freshwater biodiversity. Further actions are recommended to control pesticide use and to reduce emissions.

Identification of new, very long-chain polyunsaturated fatty acids in fish by gas chromatography coupled to quadrupole/time-of-flight mass spectrometry with atmospheric pressure chemical ionization.

The characterization of very long-chain (>C24) polyunsaturated fatty acids (VLC-PUFAs), which are essential in the vision, neural function, and reproduction of vertebrates, is challenging because of the lack of reference standards and their very low concentrations in certain lipid classes. In this research, we have developed a new methodology for VLC-PUFA identification based on gas chromatography coupled to quadrupole/time-of-flight mass spectrometry with an atmospheric pressure chemical ionization source (GC-APCI-QTOF MS). The mass accuracy attainable with the innovative QTOF instrument, together with the soft ionization of the APCI source, provides valuable information on the intact molecule, traditionally lost with electron ionization sources due to the extensive fragmentation suffered. We have identified, for the first time, VLC-PUFAs with chains up to 44 carbons in eyes, brain, and gonads of gilthead sea bream, a commercially important fish in the Mediterranean. The added value of ion mobility-mass spectrometry (IMS), recently developed in combination with GC-QTOF MS, and the contribution of the collisional cross section (CCS) parameter in the characterization of novel VLC-PUFAs (for which reference standards are not available) have been also evaluated. The methodology developed has allowed assessing qualitative differences between farmed and wild fish, and opens new perspectives in a still scarcely known field of research.

Gas chromatography-mass spectrometry based untargeted volatolomics for smoked seafood classification.

With the increase of the demand of low flavouring smoked seafood products, there is a need of methodologies able to distinguish between different seafood treatments, as not all of them are allowed in all markers. Following this objective, in the present work an untargeted volatolomics approach was applied to identify volatile markers that demonstrate that Cold smoked products can be distinguished from Tasteless smoke neither Carbon monoxide treated seafood, which are prohibited in the European Union. The use of dynamic headspace for the volatile extraction followed by thermal desorption in combination with Gas Chromatography (GC) coupled to single quadrupole Mass Spectrometry (MS) has been employed for the determination of volatile composition of smoked fish. Data processing consisted on the use of PARADISe software, applied for GC/MS data treatment, followed by the multivariate analysis with PLS_Toolbox (MATLAB), and finally the creation and validation of statistical classification model. All 107 variables obtained allowed the construction of a model reaching the correct classification of 97% of the blind samples, while a simplified model with only 11 variables correctly classified up to 93% of the blind samples. These 11 compounds were elucidated to develop subsequent target volatolomics approaches, if needed. Ordered according to the importance in the classification model, the elucidated compounds were: 3-methyl-cyclopentanone, ethylbenzene, 2-methyl-2-cyclopenten-1-one, 2-methyl-benzofuran, furfuryl alcohol, 2-acetylfuran, acetophenone, guaiacol, 1-hydroxy-2-butanone, 4-vinylguaicol and acetoin. The results demonstrated the great potential of untargeted volatolomics for smoked seafood treatments classification.

LC-MS/MS method for the determination of organophosphorus pesticides and their metabolites in salmon and zebrafish fed with plant-based feed ingredients.

The composition of Atlantic salmon feed has changed considerably over the last two decades from being marine-based (fishmeal and fish oil) to mainly containing plant ingredients. Consequently, concern related to traditional persistent contaminants typically associated with fish-based feed has been replaced by other potential contaminants not previously associated with salmon farming. This is the case for many pesticides, which are used worldwide to increase food production, and may be present in plant ingredients. Earlier studies have identified two organophosphorus pesticides, chlorpyrifos-methyl and pirimiphos-methyl, in plant ingredients used for aquafeed production. In the present study, we developed a reliable and sensitive analytical method, based on liquid chromatography coupled to tandem mass spectrometry, for the determination of these pesticides and their main metabolites in warm water (zebrafish) and cold water (Atlantic salmon) species, where possible differences in metabolites could be expected. The method was tested in whole zebrafish and in different salmon tissues, such as muscle, bile, kidney, fat, and liver. The final objective of this work was to assess kinetics of chlorpyrifos-methyl and pirimiphos-methyl and their main metabolites in fish tissue, in order to fill the knowledge gaps on these metabolites in fish tissues when fed over prolonged time.

Potential of gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry for screening and quantification of hexabromocyclododecane.

A fast method for the screening and quantification of hexabromocyclododecane (sum of all isomers) by gas chromatography using a triple quadrupole mass spectrometer with atmospheric pressure chemical ionization (GC-APCI-QqQ) is proposed. This novel procedure makes use of the soft atmospheric pressure chemical ionization source, which results in less fragmentation of the analyte than by conventional electron impact (EI) and chemical ionization (CI) sources, favoring the formation of the [M - Br](+) ion and, thus, enhancing sensitivity and selectivity. Detection was based on the consecutive loses of HBr from the [M - Br](+) ion to form the specific [M - H5Br6](+) and [M - H4Br5](+) ions, which were selected as quantitation (Q) and qualification (q) transitions, respectively. Parameters affecting ionization and MS/MS detection were studied. Method performance was also evaluated; calibration curves were found linear from 1 pg/µL to 100 pg/µL for the total HBCD concentration; instrumental detection limit was estimated to be 0.10 pg/µL; repeatability and reproducibility, expressed as relative standard deviation, were better than 7% in both cases. The application to different real samples [polyurethane foam disks (PUFs), food, and marine samples] pointed out a rapid way to identify and allow quantification of this compound together with a number of polybrominated diphenyl ethers (BDE congeners 28, 47, 66, 85, 99, 100, 153, 154, 183, 184, 191, 196, 197, and 209) and two other novel brominated flame retardants [i.e., decabromodiphenyl ethane (DBDPE) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE)] because of their presence in the same fraction when performing the usual sample treatment.

Identification of substances migrating from plastic baby bottles using a combination of low-resolution and high-resolution mass spectrometric analysers coupled to gas and liquid chromatography.

This work presents a strategy for elucidation of unknown migrants from plastic food contact materials (baby bottles) using a combination of analytical techniques in an untargeted approach. First, gas chromatography (GC) coupled to mass spectrometry (MS) in electron ionisation mode was used to identify migrants through spectral library matching. When no acceptable match was obtained, a second analysis by GC-(electron ionisation) high resolution mass spectrometry time of flight (TOF) was applied to obtain accurate mass fragmentation spectra and isotopic patterns. Databases were then searched to find a possible elemental composition for the unknown compounds. Finally, a GC hybrid quadrupole-TOF-MS with an atmospheric pressure chemical ionisation source was used to obtain the molecular ion or the protonated molecule. Accurate mass data also provided additional information on the fragmentation behaviour as two acquisition functions with different collision energies were available (MS(E) approach). In the low-energy function, limited fragmentation took place, whereas for the high-energy function, fragmentation was enhanced. For less volatile unknowns, ultra-high pressure liquid chromatography-quadrupole-TOF-MS was additionally applied. Using a home-made database containing common migrating compounds and plastic additives, tentative identification was made for several positive findings based on accurate mass of the (de)protonated molecule, product ion fragments and characteristic isotopic ions. Six illustrative examples are shown to demonstrate the modus operandi and the difficulties encountered during identification. The combination of these techniques was proven to be a powerful tool for the elucidation of unknown migrating compounds from plastic baby bottles.

Novel analytical approach for brominated flame retardants based on the use of gas chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry with emphasis in highly brominated congeners.

The analysis of brominated flame retardants (BFRs) commonly relies on the use of gas chromatography coupled to mass spectrometry (GC-MS) operating in electron ionization (EI) and electron capture negative ionization (ECNI) modes using quadrupole, triple quadrupole, ion trap, and magnetic sector analyzers. However, these brominated contaminants are examples of compounds for which a soft and robust ionization technique might be favorable since they show high fragmentation in EI and low specificity in ECNI. In addition, the low limits of quantification (0.01 ng/g) required by European Commission Recommendation 2014/118/EU on the monitoring of traces of BFRs in food put stress on the use of highly sensitive techniques/methods. In this work, a new approach for the extremely sensitive determination of BFRs taking profit of the potential of atmospheric pressure chemical ionization (APCI) combined with GC and triple quadrupole (QqQ) mass analyzer is proposed. The objective was to explore the potential of this approach for the BFRs determination in samples at pg/g levels, taking marine samples and a cream sample as a model. Ionization and fragmentation behavior of 14 PBDEs (congeners 28, 47, 66, 85, 99, 100, 153, 154, 183, 184, 191, 196, 197, and 209) and two novel BFRs, decabromodiphenyl ethane (DBDPE) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE), in the GC-APCI-MS system has been investigated. The formation of highly abundant (quasi) molecular ion was the main advantage observed in relation to EI. Thus, a notable improvement in sensitivity and specificity was observed when using it as precursor ion in tandem MS. The improved detectability (LODs < 10 fg) achieved when using APCI compared to EI has been demonstrated, which is especially relevant for highly brominated congeners. Analysis of samples from an intercomparison exercise and samples from the marine field showed the potential of this approach for the reliable identification and quantification at very low concentration levels.

Gas chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization for fluorotelomer alcohols and perfluorinated sulfonamides determination.

Ionization and in source-fragmentation behavior of four fluorotelomer alcohols (FTOH) (4:2 FTOH, 6:2 FTOH, 8:2 FTOH and 10:2 FTOH) and four N-alkyl fluorooctane sulfonamides/-ethanols (N-MeFOSA, N-EtFOSA, N-MeFOSE and N-EtFOSE) by APCI has been studied and compared with the traditionally used EI and CI. Protonated molecule was the base peak of the APCI spectrum in all cases giving the possibility of selecting it as a precursor ion for MS/MS experiments. Following, CID fragmentation showed common product ions for all FOSAs/FOSEs (C4F7 and C3F5). Nevertheless, the different functionality gave characteristic pattern fragmentations. For instance, FTOHs mainly loss H2O+HF, FOSAs showed the losses of SO2 and HF while FOSEs showed the losses of H2O and SO2. Linearity, repeatability and LODs have been studied obtaining instrumental LODs between 1 and 5fg. Finally, application to river water and influent and effluent waste water samples has been carried out in order to investigate the improvements in detection capabilities of this new source in comparison with the traditionally used EI/CI sources. Matrix effects in APCI have been evaluated in terms of signal enhancement/suppression when comparing standards in solvent and matrix. No matrix effects were observed and concentrations found in samples were in the range of 1-100pgL(-1) far below the LODs achieved with methods previously reported. Unknown related perfluoroalkyl substances, as methyl-sulfone and methyl-sulfoxide analogues for FTOHs, were also discovered and tentatively identified.

Use of electron ionization and atmospheric pressure chemical ionization in gas chromatography coupled to time-of-flight mass spectrometry for screening and identification of organic pollutants in waters.

A new approach has been developed for multiclass screening of organic contaminants in water based on the use of gas chromatography coupled to hybrid quadrupole high-resolution time-of-flight mass spectrometry with atmospheric pressure chemical ionization (GC-(APCI)QTOF MS). The soft ionization promoted by the APCI source allows effective and wide-scope screening based on the investigation of the molecular ion and/or protonated molecule. This is in contrast to electron ionization (EI) where ionization typically results in extensive fragmentation, and diagnostic ions and/or spectra need to be known a priori to facilitate detection of the analytes in the raw data. Around 170 organic contaminants from different chemical families were initially investigated by both approaches, i.e. GC-(EI)TOF and GC-(APCI)QTOF, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and a notable number of pesticides and relevant metabolites. The new GC-(APCI)QTOF MS approach easily allowed widening the number of compounds investigated (85 additional compounds), with more pesticides, personal care products (UV filters, musks), polychloronaphthalenes (PCNs), antimicrobials, insect repellents, etc., most of them considered as emerging contaminants. Both GC-(EI)TOF and GC-(APCI)QTOF methodologies have been applied, evaluating their potential for a wide-scope screening in the environmental field.

Screening of pesticides and polycyclic aromatic hydrocarbons in feeds and fish tissues by gas chromatography coupled to high-resolution mass spectrometry using atmospheric pressure chemical ionization.

This paper reports a wide-scope screening for detection and identification of pesticides and polycyclic aromatic hydrocarbons (PAHs) in feeds and fish tissues. QuEChERS sample treatment was applied, using freezing as an additional cleanup. Analysis was carried out by gas chromatography coupled to hybrid quadrupole time-of-flight mass spectrometry with atmospheric pressure chemical ionization (GC-(APCI) QTOF MS). The qualitative validation was performed for over 133 representative pesticides and 24 PAHs at 0.01 and 0.05 mg/kg. Subsequent application of the screening method to aquaculture samples made it possible to detect several compounds from the target list, such as chlorpyrifos-methyl, pirimiphos-methyl, and ethoxyquin, among others. Light PAHs (≤4 rings) were found in both animal and vegetable samples. The reliable identification of the compounds was supported by accurate mass measurements and the presence of at least two representative m/z ions in the spectrum together with the retention time of the peak, in agreement with the reference standard. Additionally, the search was widened to include other pesticides for which standards were not available, thanks to the expected presence of the protonated molecule and/or molecular ion in the APCI spectra. This could allow the detection and tentative identification of other pesticides different from those included in the validated target list.

Application of gas chromatography-(triple quadrupole) mass spectrometry with atmospheric pressure chemical ionization for the determination of multiclass pesticides in fruits and vegetables.

A multi-residue method for the determination of 142 pesticide residues in fruits and vegetables has been developed using a new atmospheric pressure chemical ionization (APCI) source for coupling gas chromatography (GC) to tandem mass spectrometry (MS). Selected reaction monitoring (SRM) mode has been applied, acquiring three transitions for each compound. In contrast to the extensive fragmentation typically obtained in classical electron ionization (EI), the soft APCI ionization allowed the selection of highly abundant protonated molecules ([M+H](+)) as precursor ions for most compounds. This was favorable for both sensitivity and selectivity. Validation of the method was performed in which both quantitative and qualitative parameters were assessed using orange, tomato and carrot samples spiked at two levels, 0.01 and 0.1mg/kg. The QuEChERS method was used for sample preparation, followed by a 10-fold dilution of the final acetonitrile extract with a mixture of hexane and acetone. Recovery and precision were satisfactory in the three matrices, at both concentration levels. Very low limits of detection (down 0.01µg/kg for the most sensitive compounds) were achieved. Ion ratios were consistent and identification according to EU criteria was possible in 80% (0.01mg/kg) to 96% (0.1mg/kg) of the pesticide/matrix combinations. The method was applied to the analysis of various fruits and vegetables from the Mediterranean region of Spain.

Improved gas chromatography-tandem mass spectrometry determination of pesticide residues making use of atmospheric pressure chemical ionization.

The capabilities of a recently launched atmospheric pressure chemical ionization (APCI) source for mass spectrometry (MS) coupled to gas chromatography (GC) have been tested in order to evaluate its potential in pesticide residue analysis in fruits and vegetables. Twenty-five pesticides were selected due to their high fragmentation under electron ionization (EI), making that the molecular ion (M+) is practically absent in their spectra. The fragmentation of these pesticides under APCI conditions was studied, with the result that M+ was not only present but also highly abundant for most compounds, with noticeable differences in the fragmentation patterns in comparison with EI. Moreover, the addition of water as modifier was tested to promote the formation of protonated molecules ([M+H]+). Under these conditions, [M+H]+ became the base peak of the spectrum for the majority of compounds, thus leading to an increase of sensitivity in the subsequent GC-MS/MS method developed using triple quadrupole analyzer (QqQ). Highly satisfactory sensitivity and precision, in terms of repeatability, were reached and linearity was satisfactory in the range 0.01-100 ng/mL. The developed methodology was applied to apple, orange, tomato and carrot QuEChERS fortified extracts in order to evaluate the matrix effects. In summary, the soft and reproducible ionization in the APCI source has greatly favored the formation of [M+H]+ oppositely to EI where abundant fragmentation occurs and where the molecular ions have low abundance or are even absent in the mass spectrum. In this way, the use of APCI has facilitated the development of tandem MS methods based on the selection of abundant [M+H]+ as precursor ion.

Characterization of the organic contamination pattern of a hyper-saline ecosystem by rapid screening using gas chromatography coupled to high-resolution time-of-flight mass spectrometry.

In this paper, gas chromatography coupled to high-resolution time-of-flight mass spectrometry (GC-TOF MS) has been applied to evaluate organic pollution in a hyper-saline aquatic environment. Firstly, a target screening was made for a list of 150 GC-amenable organic micro-contaminants, including PAHs, octyl/nonyl phenols, PCBs, PBDEs, and a notable number of pesticides, such us insecticides (organochlorines, organophosphorus, carbamates and pyrethroids), herbicides (triazines and chloroacetanilides), fungicides and several transformation products. This methodology was applied to brine samples, with a salt content from 112 g/L to saturation, and to samples from Artemia populations (crustacean Anostraca) collected during 1 year from three sampling stations in saltworks bodies sited in the Ebro river delta. Around 50 target contaminants, belong to chemical families included in the list of priority substances within the framework on European water policy. Additionally, a non-target analysis was performed in both types of samples with the objective of investigating the presence of other non-selected organic compounds taking advantage of the potential of GC-TOF MS (high sensitivity in full-spectrum acquisition mode, accurate mass measurements) for searching unknowns. Organophosphorus pesticides were the contaminants more frequently detected in brine samples. Other compounds usually present in urban and industrial wastewaters, like caffeine, methylparaben, butylated-hydroxytoluene and N-butylbenzenesulfonamide were also detected in brines. The herbicide simazine and the insecticide chlorpyrifos were among the contaminants detected in Artemia samples. Results of this work reveal a potential threat to vulnerable populations inhabiting the hyper-saline ecosystem. The valuable contribution of GC-TOF MS in environmental analysis, allowing the rapid screening of a large number of organic contaminants, is also demonstrated in this paper.

Multiclass determination of 66 organic micropollutants in environmental water samples by fast gas chromatography-mass spectrometry.

A multiresidue method has been developed for quantification and identification of 66 multiclass priority organic pollutants in water by fast gas chromatography (GC) coupled to mass spectrometry (MS). Capabilities and limitations of single quadrupole mass spectrometer as detector in fast GC were studied evaluating the chromatographic responses in terms of sensitivity and chromatographic peak shapes, as they were influenced by scan time. The number of monitored ions in a selected ion monitoring (SIM) group strongly conditioned the scan time and subsequently the number of data points per peak. A compromise between peak shape and scan time was adopted in order to reach the proper conditions for quantitative analysis. An average of 10-15 points per peak was attained for most compounds, involving scan times between 0.1 and 0.22 s. The method was validated for mineral, surface, and groundwater. A solid-phase extraction pre-concentration step using C(18) cartridges was applied. Four isotopically labeled standards were added to the samples before extraction and used as surrogates to ensure a reliable quantification. Analyses were performed by GC-MS in electron ionization mode, monitoring the three most abundant and/or specific ions for each compound and using the intensity ratios as a confirmatory parameter. With a chromatographic run of less than 10 min, SIM mode provided excellent sensitivity and identification capability due to the monitoring of three ions and the evaluation of their intensity ratio. Limits of detection below 10 ng/L were reached for most of the 66 compounds in the three matrices studied. Accuracy and precision of the method were evaluated by means of recovery experiments at two fortification levels (10 and 100 ng/L), obtaining recoveries between 70% and 120% in most cases and relative standard deviations below 20%. The possibilities of a simultaneous SIM scan method have also been explored for non-target qualitative analysis. The developed method has been applied to the analysis of surface water samples collected from the Mediterranean region of Spain.

Non-target screening of organic contaminants in marine salts by gas chromatography coupled to high-resolution time-of-flight mass spectrometry.

Gas chromatography coupled to time-of-flight mass spectrometry (GC-TOF MS) has been applied to characterize the organic pollution pattern of marine salt samples collected in saltworks from the Spanish Mediterranean coast. After dissolving the samples in water, a solid-phase extraction was applied reaching with a 250-preconcentration factor. The screening methodology allowed the detection of sample components without any kind of pre-selection of target pollutants. The identity of components detected was established by accurate mass measurements and comparison of experimental full-acquisition spectra with theoretical MS libraries. Several organic pollutants were identified in the samples, like plasticizers - potentially toxic to humans - and fragrances -included within the group of pharmaceuticals and personal care products-, among others. Our results indicate that these contaminants can be found in the marine salt after the crystallization process. GC-TOF MS is a powerful technique for wide-scope screening of (semi)volatile, low-polar organic contaminants, able to investigate the presence of a large number of compounds. Searching of contaminants is not restricted to a target list of compounds. Therefore, unexpected contaminants can be discovered in an efficient way, with better sensitivity and selectivity than other conventional analytical techniques, and making use of the powerful qualitative information provided by full-spectrum acquisition at accurate mass.

Use of soft and hard ionization techniques for elucidation of unknown compounds by gas chromatography/time-of-flight mass spectrometry.

Investigation of trace-level non-target compounds by gas chromatography/mass spectrometry (GC/MS) often is a challenging task that requires powerful software tools to detect the unknown components, to obtain the deconvoluted mass spectra, and to interpret the data if no acceptable library match is obtained. In this paper, the complementary use of electron ionization (EI) and chemical ionization (CI) is investigated in combination with GC/time-of-flight (TOF) MS for the elucidation of organic non-target (micro)contaminants in water samples. Based on accurate mass measurement of the molecular and fragment ions from the TOF MS, empirical formulae were calculated. Isotopic patterns, carbon number prediction filter and nitrogen rule were used to reduce the number of possible formulae. The candidate formulae were searched in databases to find possible chemical structures. Selection from possible structure candidates was achieved using information on substructures and observed neutral losses derived from the fragment ions. Four typical examples (bifenazate, boscalid, epoxiconazole, and fenhexamid) are used to illustrate the methodology applied and the various difficulties encountered in this process. Our results indicate that elucidation of unknowns cannot be achieved by following a standardized procedure, as both expertise and creativity are necessary in the process.

Development and validation of a rapid and wide-scope qualitative screening method for detection and identification of organic pollutants in natural water and wastewater by gas chromatography time-of-flight mass spectrometry.

In this work, a multiclass screening method for organic contaminants in natural and wastewater has been developed and validated for qualitative purposes, i.e. to ensure the reliable and sensitive identification of compounds detected in samples at a certain level of concentration. The screening is based on the use of GC-TOF MS, and the sample procedure involves solid phase extraction with C(18) cartridges. Around 150 organic contaminants from different chemical families were investigated, including PAHs, octyl/nonyl phenols, PCBs, PBDEs and a notable number of pesticides, such as insecticides (organochlorines, organophosphorus, carbamates and pyrethroids), herbicides (triazines and chloroacetanilides), fungicides and several relevant metabolites. Surface water, ground water and effluent wastewater were spiked with all target analytes at three concentration levels (0.02, 0.1 and 1 µg/L). Influent wastewater and raw leachate from a municipal solid waste treatment plant were spiked at two levels (0.1 and 1 µg/L). Up to five m/z ions were evaluated for every compound. The identification criterion was the presence of, at least, two m/z ions at the expected retention time, measured at their accurate mass, and the accomplishment of the Q/q(i) intensity ratio within specified tolerances. The vast majority of compounds investigated were correctly identified in the samples spiked at 1 µg/L. When analyte concentration was lowered down to 0.1 µg/L the identification was more problematic, especially in complex-matrix samples like influent wastewater. On the contrary, many contaminants could be properly identified at the lowest level 0.02 µg/L in cleaner matrices. The procedure was applied to the screening of water samples of different origin and matrix composition and allowed the detection of several target contaminants. A highly reliable identification could be carried out thanks to the sensitive full-spectrum acquisition at accurate mass, the high selectivity reached with the use of narrow-mass window extracted ion chromatograms, the low mass errors observed in the positive detections and the Q/q ratio accomplishment.

GC-MS/MS multi-residue method for the determination of organochlorine pesticides, polychlorinated biphenyls and polybrominated diphenyl ethers in human breast tissues.

In this work, a multiresidue method for the quantification and confirmation of around 30 organohalogenated compounds in human breast tissue samples has been developed. Analytes tested included organochlorine (OC) (pesticides and polychlorinated biphenyls) and organobromine (OBr) (polybrominated diphenyl ether) compounds. The approach is based on a simple extraction with hexane, followed by a SPE clean-up using silica cartridges and final measurement by GC coupled to triple quadrupole MS. Analyses were performed in both ionizations, electron impact (EI) (selected reaction monitoring (SRM) mode) and negative chemical ionization (NCI) (selected ion recording (SIR) mode). Three isotopically labeled standards were added before extraction and used as surrogates: HCB-13C6, lindane-D6 and p,p'-DDE-D8. The method was validated in terms of accuracy, precision, LOQ and LOD and confirmation reliability, using breast tissue spiked at three concentration levels in the range 1-100 ng/g for OC compounds and at two levels 0.1 and 10 ng/g for OBr compounds (0.5 and 50 ng/g for BDE 209). The usefulness of the developed method was tested by the analysis of real human samples, giving as a result the detection of several OC and OBr compounds in different samples analyzed. The acquisition of at least two SRM transitions (in EI) or ions (in NCI) per analyte allowed positive findings to be confirmed by accomplishment of ion ratios between the quantification and the confirmation transitions or ions.