Comparison of tandem-in-space and tandem-in-time mass spectrometry in gas chromatography determination of pesticides: Application to simple and complex food samples

Simultaneous determination of boscalid and fludioxonil in grape and soil under field conditions by gas chromatography/tandem triple quadrupole mass spectrometry

A gas chromatography-tandem mass spectrometry method was developed and validated to simultaneously determine boscalid and fludioxonil in grape and soil samples. These samples were extracted with 10 mL of acetonitrile and purified using a mixed primary secondary amine/octadecylsilane sorbent. The method showed good linearity (R²  > 0.99) in the calibration range 0.005-2 μg/mL for both pesticides. The limits of detection and quantification for the two analytes in grape and soil were 0.006 and 0.02 mg/kg, respectively. Fungicide recoveries in grape and soil were 81.18-92.11% for boscalid and 82.73-97.67% for fludioxonil with relative standard deviations of 1.31-10.31%. The established method was successfully applied to the residual analysis of boscalid and fludioxonil in real grape and soil samples. The terminal residue concentrations of boscalid and fludioxonil in grape samples collected from Anhui and Guizhou were <5 mg/kg (the maximum residue limit set by China) 7 days after the last application and 1 mg/kg (the maximum residue limit set by USA) 14 days after the last application. These results could provide guidance for the proper and safe use of boscalid and fludioxonil in grape and help the Chinese government to establish an MRL for fludioxonil in grape.

Preferential alkali metal adduct formation by cis geometrical isomers of dicaffeoylquinic acids allows for efficient discrimination from their trans isomers during ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry

RATIONALE

Caffeoylquinic acid (CQA) derivatives are a group of structurally diverse phytochemicals that have attracted attention due to their many health benefits. The structural diversity of these molecules is due in part to the presence of regio- and geometrical isomerism. This structural diversity hampers the accurate annotation of these molecules in plant extracts. Mass spectrometry (MS) is successfully used to differentiate between the different regioisomers of the CQA derivatives; however, the accurate discrimination of the geometrical isomers of these molecules has proven to be an elusive task.

METHODS

UV-irradiated methanolic solutions of diCQA were analyzed using an ultra-high-performance liquid chromatography/quadrupole time-of-flight mass spectrometry (UHPLC/QTOFMS) method in negative ionisation mode. An in-source collision-induced dissociation (ISCID) method was optimized by varying both the capillary and cone voltages to achieve differential fragmentation patterns between UV-generated geometrical isomers of the diCQAs during MS analyses.

RESULTS

Changes in the capillary voltage did not cause a significant difference to the fragmentation patterns of the four geometrical isomers, while changes in the cone voltage resulted in significant differences in the fragmentation patterns. The results also show, for the first time, the preferential formation of alkali metal (Li(+), Na(+) and K(+)) adducts by the cis geometrical isomers of diCQAs, compared to their trans counterparts.

CONCLUSIONS

Optimized QTOFMS-based methods may be used to differentiate the geometrical isomers of diCQAs. Finally, additives such as metal salts to induce adduct formation can be applied as an alternative method to differentiate closely related isomers which could have been difficult to differentiate under normal MS settings.

Picogram per liter detections of pyrethroids and organophosphates in surface waters using passive sampling

Pyrethroids and organophosphates are among the most toxic insecticides for aquatic organisms, leading to annual-average environmental quality standards (AA-EQS) in the picogram per liter range in surface waters. For monitoring purposes, it is therefore crucial to develop very sensitive analytical methods. Until now, it is very difficult to reach detection limits at or below given AA-EQSs. Here, we present a passive sampling method using silicone rubber (SR) sheets for the sampling of ten pyrethroids and two organophosphates in surface waters. An analytical method was developed, optimized and validated for the extraction of the insecticides from the SR sheets by accelerated solvent extraction followed by clean-up on C18 and silica gel and detection with GC-MS/MS in positive ionization mode. Good precision (<20%) and absolute recovery (>50%) was observed for all substances, accuracy was between 66% and 139%. Limits of detection between 6 and 200 pg/L were achieved for all substances in surface waters using average sampling rates for PCBs and PAHs. The lack of substance-specific sampling rates and missing performance reference compounds led to an uncertainty in the concentration estimation of factor three in both directions. In a large field study, comprising 40 environmental samples from nine Swiss rivers, eight out of 12 substances were detected (most frequently: chlorpyrifos, cypermethrin). Most of the estimated organophosphate concentrations were between 0.1 and 1 ng/L, most pyrethroid detections below 0.1 ng/L. Four substances (chlorpyrifos-methyl, cypermethrin, deltamethrin and lambda-cyhalothrin) showed exceedances of their respective AA-EQS in multiple samples, also when the uncertainties in the concentration estimation were considered. As pyrethroid and organophosphate detection by SR passive sampling is very practicable and allows sensitive analysis, it has the potential to become a new tool in the monitoring of non-polar pesticides.

Determination of polar organic compounds in atmospheric aerosols by gas chromatography with ion trap tandem mass spectrometry

A gas chromatography with ion trap mass spectrometry method has been developed and validated for the analysis of 27 polar organic compounds in atmospheric aerosols. The target analytes were low-molecular-weight carboxylic acids and methoxyphenols, as relevant markers of source emissions and photochemical processes of organic aerosols. The operative parameters were optimized in order to achieve the best sensitivity and selectivity for the analysis. In comparison with the previous gas chromatography with mass spectrometry procedure based on single ion monitoring detection, the tandem mass spectrometry technique increased the analytical sensitivity by reducing detection limits for standard solutions from 1-2.6 to 0.1-0.4 ng/μL ranges (concentrations in the injected solution). In addition, it enhanced selectivity by reducing matrix interferences and chemical noise in the chromatogram. The applicability of the developed method in air quality monitoring campaigns was effectively checked by analyzing environmental samples collected in the Po Valley (Northern Italy) in different seasons. The obtained results indicate that the ion trap mass spectrometer may be an ideal alternative to high-resolution mass spectrometers for the user-friendly and cost-effective determination of a wide range of molecular tracers in airborne particulate matter.

Ability of NIRS technology to determine pesticides in liquid samples at maximum residue levels

BACKGROUND

Pesticide residues remaining on food represent a potential risk to consumer's health. Determination of these pesticide residues involves tedious procedures of analysis with regard to time and laboratory work. Near-infrared spectroscopy (NIRS) is a possible alternative to these methods. The aim of this research was to evaluate the ability of NIRS to classify two pesticides used for controlling apple fruit pests according to their concentration. Different solutions were prepared, based on the dose recommended by the pesticide producers for apple pest treatments. Spectra were acquired on a spectrophotometer from liquid samples belonging to these solutions.

RESULTS

Calibration models were developed from liquid samples, following the soft independent modelling of class analogy (SIMCA) analysis method. These models classified between 99 and 100% of the validation samples belonging to different pesticide concentration solutions even at the maximum residue limit level of these products in apple fruit.

CONCLUSIONS

NIRS technology shows a high potential for identifying pesticides in liquid samples, according to their concentration, at the levels required by the legislation.

Determination of residual flubendiamide in the cabbage by QuEChERS-liquid chromatography-tandem mass spectrometry

Flubendiamide, which belongs to the new chemical class of phthalic acid diamides, is widely used against lepidopteron pests in a variety of vegetable and rice pests. It provides superior plant protection against a broad range of economically important lepidopterous pests, including Spodoptera exigua and Plutella xylostella. A determination method of flubendiamide in the cabbage was established in this paper. Flubendiamide in the cabbage was extracted with acetonitrile and ultrasonic extraction, and was purified by QuEChERS and analyzed by LC-MS/MS (liquid chromatography-tandem mass spectrometry). The results indicated that the average recovery of flubendiamide in the cabbage was 81.27%-91.45%, the coefficient of variation was 1.79%-4.81%, and the lowest detection concentration was 0.3 μg/kg. The extraction of flubendiamide from the cabbage and its analysis was in accordance with the pesticide residue criterion, i.e., simple, rapid, accurate, reproducible, stable, separatory, and convenient. It identifies and quantifies trace-level flubendiamide residues in the cabbage extracts using LC-MS/MS in the ESI negative mode coupled with the QuEChERS method.

Biophysical influence of isocarbophos on bovine serum albumin: spectroscopic probing

Isocarbophos (ICP) is a phosphorous pesticide with high toxicity. It has been detected in several kinds of food and therefore can enter human body. In this paper, spectroscopic approaches including three-dimensional fluorescence (3D-FL) spectroscopy, UV-visible absorption spectroscopy and circular dichroism (CD) spectroscopy were employed to explore the binding of ICP to bovine serum albumin (BSA) at simulated physiological conditions. It was found that the fluorescence quenching of BSA was caused by the formation of ICP-BSA complex at ground state and belonged to static quenching mechanism. The binding constants, the number of binding sites, enthalpy change (ΔH(θ)), Gibbs free energy change (ΔG(θ)) and entropy change (ΔS(θ)) were calculated at four different temperatures according to Scatchard model and thermodynamic equations. To identify the binding location, fluorescence probe techniques were used. The results showed that warfarin, an acknowledged site marker for BSA, could be partially replaced by ICP when ICP was added to warfarin-BSA systems, which demonstrated that ICP primarily bound on Sudlow's site I in domain IIA of BSA molecule. The distance r (3.06 nm) between donor (Trp-212) and acceptor (ICP) was obtained based on Förster's non-radiation fluorescence resonance energy transfer (FRET) theory. Furthermore, the CD spectral results indicated that the secondary structure of BSA was changed in presence of ICP. The study is helpful to evaluating the toxicology of ICP and understanding its effects on the function of protein during the blood transportation process.

Multiresidue pesticide analysis in Korean ginseng by gas chromatography-triple quadrupole tandem mass spectrometry

In this study, a new analytical method was developed based on gas chromatography-triple quadrupole tandem mass spectrometry (GC-MS/MS) and used to determine 32 multiclass pesticides in ginseng products. The analytical method was validated, yielding recovery rates in the range of 55.2-108.3%, with precision values expressed as relative standard deviation (RSD) lower or equal to 12% at the spiking levels of 30, 100, and 1000 μg/kg. Correlation coefficients and LOQs (limit of quantification) were in the range 0.9801-0.9989 and 0.15-70 g/kg, respectively. With these validation data and this method, multiresidue pesticides of ginseng samples (fresh ginseng (n=118), red ginseng (n=24), dried ginseng (n=10)) were analysed. Among them, the most frequently detected pesticide was tolclofos-methyl. Tolclofos-methyl was detected in 86.4% of fresh ginseng (18.25-404.5 μg/kg), 91.7% of red ginseng (13.14-119.4 μg/kg), and 87.5% of dried ginseng (23.15-3673 μg/kg).

New trends in quantification of acrylamide in food products

Methods applied in acrylamide quantification in foods have been reviewed in this paper. Novel analytical techniques like capillary electrophoresis (CE), immunoenzymatic test (ELISA) and electrochemical biosensors, which can replace traditional methods like high performance liquid chromatography (HPLC) and gas chromatography (GC) were presented. Short time of analysis and high resolution power of electrophoretic techniques caused that they became routinely used in food analysis apart from high performance liquid chromatography and gas chromatography. Application of modern chromatography methods like ultra performance liquid chromatography (UPLC) in acrylamide quantification considerably shortened the time of analysis and decreased the consumption of indispensable reagents. The most promising approaches to acrylamide quantification in foods are electrochemical biosensors and immunoenzymatic tests. In contrast to chromatography and electrophoretic methods they require neither expensive equipment nor time consuming sample preparation and allow for fast screening of numerous samples without the usage of sophisticated apparatuses. Because of many advantages such as miniaturization, rapid and simple analysis, and high sensitivity and selectivity, biosensors are thought to replace conventional methods of acrylamide quantification in food.

Current mass spectrometry strategies for the analysis of pesticides and their metabolites in food and water matrices

Analysis of pesticides and their metabolites in food and water matrices continues to be an active research area closely related to food safety and environmental issues. This review discusses the most widely applied mass spectrometric (MS) approaches to pesticide residues analysis over the last few years. The main techniques for sample preparation remain solvent extraction and solid-phase extraction. The QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) approach is being increasingly used for the development of multi-class pesticide residues methods in various sample matrices. MS detectors-triple quadrupole (QqQ), ion-trap (IT), quadrupole linear ion trap (QqLIT), time-of-flight (TOF), and quadrupole time-of-flight (QqTOF)-have been established as powerful analytical tools sharing a primary role in the detection/quantification and/or identification/confirmation of pesticides and their metabolites. Recent developments in analytical instrumentation have enabled coupling of ultra-performance liquid chromatography (UPLC) and fast gas chromatography (GC) with MS detectors, and faster analysis for a greater number of pesticides. The newly developed "ambient-ionization" MS techniques (e.g., desorption electrospray ionization, DESI, and direct analysis in real time, DART) hyphenated with high-resolution MS platforms without liquid chromatography separation, and sometimes with minimum pre-treatment, have shown potential for pesticide residue screening. The recently introduced Orbitrap mass spectrometers can provide high resolving power and mass accuracy, to tackle complex analytical problems involved in pesticide residue analysis.

Organochlorine pesticide residues in strawberries from integrated pest management and organic farming

A rapid, specific, and sensitive method based on the Quick Easy Cheap Effective Rugged and Safe (QuEChERS) method and a cleanup using dispersive solid-phase extraction with MgSO(4), PSA, and C18 sorbents has been developed for the routine analysis of 14 pesticides in strawberries. The analyses were performed by three different analytical methodologies: gas chromatography (GC) with electron capture detection (ECD), mass spectrometry (MS), and tandem mass spectrometry (MS/MS). The recoveries for all the pesticides studied were from 46 to 128%, with relative standard deviation of <15% in the concentration range of 0.005-0.250 mg/kg. The limit of detection (LOD) for all compounds met maximum residue limits (MRL) accepted in Portugal for organochlorine pesticides (OCP). A survey study of strawberries produced in Portugal in the years 2009-2010 obtained from organic farming (OF) and integrated pest management (IPM) was developed. Lindane and β-endosulfan were detected above the MRL in OF and IPM. Other OCP (aldrin, o,p'-DDT and their metabolites, and methoxychlor) were found below the MRL. The OCP residues detected decreased from 2009 to 2010. The QuEChERS method was successfully applied to the analysis of strawberry samples.

Performance of gas chromatography/tandem mass spectrometry in the analysis of pyrethroid insecticides in environmental and food samples

The performance of gas chromatography coupled with tandem mass spectrometry (GC/MS/MS) was tested for the simultaneous determination of twelve pyrethroid insecticides. First, a comparison of two different ionization modes, electron ionization (EI) and negative chemical ionization (NCI), was carried out using MS and MS/MS. NCI-MS/MS provided the best results in terms of selectivity and sensitivity giving very low detection limits of 0.11 to 450 fg injected. The reliability of the method was confirmed through the evaluation of quality parameters such as accuracy (70-100%), and repeatability and reproducibility, with coefficients of variation below 15% and 10%, respectively. The applicability of the GC/MS/MS method to real samples and influence of matrix effects were evaluated through the analysis of spiked water, sediment and milk at 0.25 ng L(-1) , 5 ng g(-1) dry weight (dw) and 25 ng g(-1) (dw), respectively, of each pyrethroid insecticide considered. Using GC/NCI-MS/MS, matrix spectral interferences were minimized providing method limits of detection (MLODs) of 0.05-2.59 ng L(-1) , 0.10-87.7 pg g(-1) dw, 2.29-1071 pg g(-1) lipid weight (lw) for water, sediment and milk, respectively. To the best of our knowledge, the MLOD values found in our study were better than those reported in previous studies; in particular for sediment and food samples, they were one order of magnitude lower.

Evaluation of two liquid chromatography/tandem mass spectrometry platforms for quantification of monensin in animal feed and milk

Monensin is an anticoccidial drug that has been used as an additive in medicated feed. The United States Food and Drug Administration (USFDA) has included monensin in the national surveillance schemes for residues in foodstuff. In this study, two simple, selective and rapid methods were developed to determine monensin content in animal feed and milk. The methods enabled the detection of monensin residues as low as 1 ppb. Moreover, the two methods were used as models to compare two common liquid chromatography/tandem mass spectrometry (LC/MS/MS) platforms; an LC linear ion trap (LC/LIT) and an LC triple quadrupole (LC/QqQ). The two instrument platforms were evaluated for their matrix effect dependence, precision and accuracy. The LC/QqQ presented a lower limit of detection and limit of quantitation (LOD and LOQ) and showed less matrix dependence as compared to the LC/LIT. The LC/QqQ instrument also demonstrated a better intermediate precision. For example, the intermediate precision standard deviation calculated for 27 analyses across three days was 4% and 11% for LC/QqQ and LC/LIT, respectively. Overall, the LC/QqQ represents a better choice for analysis of monensin with respect to LOD, LOQ, matrix interference and precision.

Method validation and comparison of acetonitrile and acetone extraction for the analysis of 169 pesticides in soya grain by liquid chromatography-tandem mass spectrometry

An acetonitrile-based extraction method for the analysis of 169 pesticides in soya grain, using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in the positive and negative electrospray ionization (ESI) mode, has been optimized and validated. This method has been compared with our earlier published acetone-based extraction method, as part of a comprehensive study of both extraction methods, in combination with various gas chromatography-(tandem) mass spectrometry [GC-MS(/MS)] and LC-MS/MS techniques, using different detection modes. Linearity of calibration curves, instrument limits of detection (LODs) and matrix effects were evaluated by preparing standards in solvent and in the two soya matrix extracts from acetone and acetonitrile extractions, at seven levels, with six replicate injections per level. Limits of detection were calculated based on practically realized repeatability relative standard deviations (RSDs), rather than based on (extrapolated) signal/noise ratios. Accuracies (as % recoveries), precision (as repeatability of recovery experiments) and method limits of quantification (LOQs) were compared. The acetonitrile method consists of the extraction of a 2-g sample with 20 mL of acetonitrile (containing 1% acetic acid), followed by a partitioning step with magnesium sulphate and a subsequent buffering step with sodium acetate. After mixing an aliquot with methanol, the extract can be injected directly into the LC-MS/MS system, without any cleanup. Cleanup hardly improved selectivity and appeared to have minor changes of the matrix effect, as was earlier noticed for the acetone method. Good linearity of the calibration curves was obtained over the range from 0.1 or 0.25 to 10 ng mL(-1), with r(2)>or=0.99. Instrument LOD values generally varied from 0.1 to 0.25 ng mL(-1), for both methods. Matrix effects were not significant or negligible for nearly all pesticides. Recoveries were in the range 70-120%, with RSD Collapse

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MESH Headings

• Acetone/chemistry
• Acetonitriles/chemistry
• Calibration
• Chromatography, Liquid/methods
• Pesticide Residues/analysis
• Pesticides/analysis
• Plant Extracts/chemistry
• Reproducibility of Results
• Seeds/chemistry
• Glycine max/chemistry
• Tandem Mass Spectrometry/methods

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Affiliation(s)

Ionara R Pizzutti Chemistry Department, Federal University of Santa Maria, Center of Research and Analysis of Residues and Contaminants, Santa Maria, RS, Brazil.
André de Kok
Maurice Hiemstra
Cristine Wickert
Osmar D Prestes

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