Does further clean-up reduce the matrix enhancement effect in gas chromatographic analysis of pesticide residues in food?

Simultaneous Analysis of 272 Pesticides in Agricultural Products by the QuEChERS Method and Gas Chromatography with Tandem Mass Spectrometry

The aim of this study is to develop a rapid and accurate method for simultaneous analysis of multi-residue pesticides and conduct pesticide monitoring in agricultural products produced by the production and distribution stage in Korea. The representative agricultural products were selected as brown rice, soybean, potato, mandarin, and green pepper and developed using gas chromatography with tandem mass (GC-MS/MS) for the analysis of 272 pesticide residues. The experimental samples were extracted by the QuEChERS-EN method and then cleaned up by using d-SPE, including MgSO4 and primary secondary amine (PSA) sorbents. The established method was validated in accordance with Codex CAC-GL/40, and the limit of quantitation (LOQ) was determined to be 0.01 mg/kg. A total of 243 pesticides satisfied the guidelines in five samples at three levels with values of 60 to 120% (recovery) and ≤45% (coefficient of variation, CV). The remaining 29 pesticides did not satisfy the guidelines, and these pesticides are expected to be used as a screening method for the routine inspection of agricultural products. As a result of analyzing 223 agricultural products in South Korea by applying the simultaneous analysis method, none of the detected levels in the samples exceeded the standard values based on maximum residue limits (MRLs). The developed method in this study will be used to inspect residual pesticides in agricultural products, and it is anticipated to contribute to the distribution of safe agricultural products to consumers.

Application of the Bland-Altman and Receiver Operating Characteristic (ROC) Approaches to Study Isotope Effects in Gas Chromatography-Mass Spectrometry Analysis of Human Plasma, Serum and Urine Samples

The Bland-Altman approach is one of the most widely used mathematical approaches for method comparison and analytical agreement. This work describes, for the first time, the application of Bland-Altman to study 14N/15N and 1H/2H (D) chromatographic isotope effects of endogenous analytes of the L-arginine/nitric oxide pathway in human plasma, serum and urine samples in GC-MS. The investigated analytes included arginine, asymmetric dimethylarginine, dimethylamine, nitrite, nitrate and creatinine. There was a close correlation between the percentage difference of the retention times of the isotopologs of the Bland-Altman approach and the area under the curve (AUC) values of the receiver operating characteristic (ROC) approach (r = 0.8619, p = 0.0047). The results of the study suggest that the chromatographic isotope effects in GC-MS result from differences in the interaction strengths of H/D isotopes in the derivatives with the hydrophobic stationary phase of the GC column. D atoms attenuate the interaction of the skeleton of the molecules with the lipophilic GC stationary phase. Differences in isotope effects in plasma or serum and urine in GC-MS are suggested to be due to a kind of matrix effect, and this remains to be investigated in forthcoming studies using Bland-Altman and ROC approaches.

Improved analysis of folpet and captan in foods using liquid chromatography-triple quadrupole linear ion trap mass spectrometry: applying mass filtering, collision, and trapping conditions

Accurate and highly sensitive analysis of folpet and captan was accomplished using liquid chromatography-triple quadrupole linear ion trap mass spectrometry (LC-QqQIT) with selective ion mode; mass filtering, collision, and trapping condition. Dimensional mass spectrometry (MS³) parameters were optimized for the residue detection of folpet and captan in six food commodities (apples, tomatoes, sweet pepper, wheat flour, sesame seeds, and fennel seeds). The sample preparation method was based on the known QuEChERS protocol, except a mixture of acetonitrile/acetone was used for the sample extraction from the sesame seeds. The robustness and reliability of the developed MS³ method were demonstrated by performing a full validation, according to SANTE/11312/2021, at 0.01-0.25 mg/kg. Recovery ranged from 83 to 118% with a relative standard deviation below 19% in all the tested commodities, and limits of quantifications (LOQs) were 0.01 mg/kg in apples and tomatoes; 0.03 mg/kg in sweet pepper; and 0.05 mg/kg in wheat flour, sesame seeds, and fennel seeds. Monitoring results showed that about 90% of apples contained captan residue, and in sweet pepper, concentrations of captan and folpet as high as 1.57 and 0.97 mg/kg were found, respectively. The novel developed MS³ method enabled more reliable identification of these commonly problematic fungicides at lower LOQs than previously reported methods.

Development and validation of a GC-MS method for analysis of Dithiocarbamate Fungicide residues in the Spices Cardamom (Elettaria cardamomom) and black pepper (Piper nigrum)

Dithiocarbamates constitute an important class of broad-spectrum antifungal compounds used extensively in agriculture, including in the cultivation of spices. Maximum residue limits for these compounds have been enforced by several importing countries in international food trade. Validation of analytical methods for dithiocarbamates in spices have not been reported previously. A quick and sensitive method for estimation of total dithiocarbamates as carbon disulphide (CS2) using GC-MS in two major spices, viz. small cardamom (Elettaria cardamomom) and black pepper (Piper nigrum) was optimized and validated. Dithiocarbamate residues in these spice matrices were extracted and subjected to acid hydrolysis followed by reduction to CS2, which was then quantitatively absorbed into isooctane and analysed using GC-MS, employing selected ion monitoring and post-run mid-column backflush technique. For fortification levels from 0.1 to 1.0 mg kg- 1, recoveries obtained ranged from 75 to 98% in cardamom and 76-98% in black pepper, with intra-day precision (RSDr) < 12% and inter-day precision (RSDR) < 15% in all cases. Limit of Quantification of 0.05 mg kg- 1 was achieved in both spices. It was found that there was negligible interference in quantitative accuracy due to essential oils present in the two spices studied. Matrix effect was seen to be suppressive in the two spices studied, and sufficiently low to exclude the use of matrix-matched calibration in routine quantitative analysis. The optimized analytical method was found to be suitable for evaluation of compliance of real samples against the Codex maximum residue limits for cardamom and black pepper. Safety evaluation for human consumption, based on the incidence of Dithiocarbamate residues, was performed in real samples of cardamom and black pepper. This method offers the possibility of extending applicability to other spices also.

Supplementary information

The online version contains supplementary material available at 10.1007/s13197-022-05462-9.

Sandwich injection and analyte protectants as a way to decrease the drift due to matrix effect between bracketing calibration in GC-MS/MS: A case study

In pesticide residues analysis, the drift is the difference between the concentration of two bracketing calibrations in the same batch. According to the SANTE/12682/2019 guideline a criterion of ±30% must be met or positive samples should be reanalyzed. This study aimed to investigate, for the first time, the efficiency of using analyte protectants (Aps) and the sandwich injection approach (SIA) to eliminate the drift between bracketing matrix matched-calibrations taking strawberry as an example. The strawberry samples were prepared according to the citrate-buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure, followed by solvent exchange from acetonitrile to n-hexane:actone (9:1). Two batches were injected with the same sequence on GC-MS/MS, the only difference was that the first batch was without Aps and the second was with Aps. The sequence of the batch was as follows: blank solvent injection, 5 strawberry matched-calibrations at 0.05 μg/ml, separated by 20 blank strawberry injections after each strawberry matched-calibration injection. The drift was measured by considering the results of the first calibration as 100% and comparing the rest 4 injections with it. After 20 injections, out of the studied 219 pesticides, more than half of the pesticides fell out of criteria when analyte protectants were not used, and by the end of the samples batch 95% of the analytes were out of criteria. Only 8% of the studied analytes were out of criteria for the Aps batch after 20 injections. In the end of the 80 samples batch, 17% were out of criteria. Furthermore, at the end of the protected matrix-matched calibration batch, 90% of the pesticides had an RSD less than 15% in comparison with only 5% of the analytes for the non-protected batch. Moreover, the non-protected batch had an obvious negative drift in comparison with the protected batch. For example, the number of pesticides that had a lower result in the second matrix matched-calibration for the non-protected batch was more than twice the number in the protected batch (194 compared to 91 out of 219 pesticides for both experiments).

Compensation of matrix effects in seed matrices followed by gas chromatography-tandem mass spectrometry analysis of pesticide residues

Despite analytical advances, matrix effects (MEs) in pesticide residue analysis by gas chromatography - tandem mass spectrometry continue to be a challenge, especially in difficult samples such as seeds. In this study, the influence of different clean-up sorbents (chitin, chitosan, Z-Sep+, EMR-Lipid) and different mixtures of primary secondary amine (PSA), C18, graphitized carbon black (GCB) and MgSO₄ were investigated in terms of MEs and recoveries in four types of seeds: cress, fennel, flax, and hemp. Additionally, different volumes of water (5, 7.5 and 10 mL) were investigated for QuEChERS extraction. Under the selected conditions: the largest volume of water (10 mL) and PSA/C18/GCB/MgSO₄ (50/150/50/50 mg, respectively) as clean-up sorbent yielded acceptable recoveries of 70-120% for most of the pesticides (211-225 out of 248 compounds) and the lowest MEs were between -20%>MEs>20% (27-50 compounds). The final method was validated for 248 pesticides with LOQs equal to 0.005 mg kg^-1. Additionally, matrix-matched calibration was used as a practical method to compensate for MEs. Among the 21 pesticides found in 12 of the samples, chlorpyrifos (0.008-1.1 mg kg^-1), tebuconazole (0.071-0.96 mg kg^-1), and trifloxystrobin (0.007-0.15 mg kg^-1) were most commonly determined.

Stereoselective Analysis of Chiral Pyrethroid Insecticides Tetramethrin and α-Cypermethrin in Fruits, Vegetables, and Cereals

This manuscript presents an effective and robust method for simultaneous stereoselective determination of two pyrethroid insecticides, tetramethrin and α-cypermethrin in different food products by high-performance liquid chromatography. Enantioseparation was carried out using reversed-phase chromatography, and the influences of four polysaccharide-based chiral columns, mobile phase composition, and column temperature on retention were fully investigated. Satisfactory separation was obtained on Chiralpak IG column using acetonitrile-water (75:25, v/v) under isocratic conditions. To extract and purify the target analytes from food matrices, matrix solid-phase dispersion was employed with C₁₈ as dispersant and primary secondary amine as well as graphitized carbon black as cleanup sorbents. Response surface method based on Box-Behnken design was implemented to assist optimization of the extraction variables. Then, method validation was done in real samples including specificity, linearity, sensitivity, trueness, precision, as well as stability, and its analytical performance fulfills the criteria recommended by the European Union SANTE/11945/2015, demonstrating its applicability in studying the stereochemistry of chiral tetramethrin and α-cypermethrin in food products.

Chitosan-reduced graphene oxide composites with 3D structures as effective reverse dispersed solid phase extraction adsorbents for pesticides analysis

Chitosan-reduced graphene oxide composites with 3D structures (3D CS-rGO) were prepared via a facile solvothermal synthetic strategy. The reduction of GO and crosslinking of rGO nanosheets with CS into 3D structures were achieved simultaneously in one step. The resulting 3D CS-rGO composite achieves high adsorption capacities of catechins, caffeine and pigments from tea acetonitrile extraction, especially for catechins, which is 10 times higher than that of GO (179.3 mg g^-1vs. 18.7 mg g^-1). The 3D CS-rGO composite exhibits the best removal efficiency of matrix interference in comparison to other traditional adsorbents, which could diminish the matrix effect on targeted pesticides by 1%-55%. A determination method of 70 kinds of pesticides is successfully established for tea based on 3D CS-rGO composite as an efficient reverse dispersed solid phase extraction adsorbent. The established method has the great advantages of operation simplicity, being time saving and high purification performance using only one kind and a low amount of adsorbent. 3D graphene based materials are expected to be promising adsorbents for sample pretreatment in trace contaminant analysis of complex food samples.

Purification Method for Multi-residual Pesticides in Green Tea

Dried green tea leaves, fortified with more than 190 multi-class pesticides, were analyzed by the newly modified Luke multiresidue method. This consists of acetone-acetonitrile extraction, dichloromethane partition and florisil cartridge purification, eluting with n-hexane-dichloromethane-acetonitrile (50:45:5), which was optimized in this study. The final sample, in n-hexane, was analyzed by GC-ECD and/or NPD. Of the 194 pesticides tested, 147 pesticides were recovered with more than 70% from dried green tea leaves. Eighteen pesticides were not recovered at all with this method.

Combined use of a modifier gas generator, analyte protectants and multiple internal standards for effective and robust compensation of matrix effects in gas chromatographic analysis of pesticides

In the analysis of pesticides performed with gas chromatography, the quantitative performance of measurements can be severely compromised by phenomena known as matrix effects. In seeking a solution to the problem of matrix effects, the application of a modifier gas generator (MGG) was investigated in this study, together with analyte protectants and multiple internal standards. Ethylene glycol (EG) was used as modifier gas and matrix effects in GCMS analysis were then evaluated by using the extracts of various food commodities. MGG was used in combination with other known methods of matrix effect compensation and its performance in reducing matrix effects tested. We have found that by combining MGG with conventional analyte protectants, matrix effects were substantially reduced for most of pesticides. Use of EG was especially effective for organophosphate pesticides and those with amino groups. Using this approach, the shortcomings of conventional analyte protectants were remedied. Although neither EG nor analyte protectants could sufficiently reduce the matrix effects for certain classes of pesticides, this limitation could be overcome with the use of multiple internal standards (IS) in the analysis. Finally, it was shown that the method we developed could achieve better analytical performance than the matrix-matched calibration method. Our method was robust with respect to the variation of food matrix components, so its application to real-world analyses would be practical and promising.

Three approaches to minimize matrix effects in residue analysis of multiclass pesticides in dried complex matrices using gas chromatography tandem mass spectrometry

This paper discusses one of the major concerns in pesticide residue analysis: the matrix effect related to gas chromatography (GC), which can adversely affect quantification. In this study, a comparison of approaches for dealing with the matrix effect was investigated for 236 pesticides in complex matrices, including dried herbs (Centaurea cyanus L., Matricaria chamomilla L., Thymus vulgaris L.) and dried fruit (currants, chokeberry), using a modified QuEChERS method and GC-MS/MS analysis. Three approaches were evaluated: (i) using matrix-matched calibration, (ii) adding a mixture of analyte protectants (APs) to every extract or (iii) injection prior to GC-MS/MS analysis. Finally, minimization of the matrix effect to the acceptable levels of -20 to 20% for over 80% of investigated pesticides was found when APs mixture was injected at the beginning of the sequence. In this approach, the matrix effects were significantly weaker for some pesticides than when matrix-matched calibration was used.

Trace Level Analysis of Sarin and VX in Food Using Normal Phase Silica Gel and Ultra-Performance Liquid Chromatography-Time-of-Flight Mass Spectrometry (UPLC-TOF-MS)

Ultra-Performance Liquid Chromatography/electrospray ionization mass spectrometry was used for the trace level determination of isopropyl methylphosphonofluoridate (Sarin, GB) and ( O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX) after extraction from various foods. A method utilizing normal phase silica gel was developed for the sample preparation and extraction of VX and GB from food. The extraction efficiencies of the normal phase silica gel method for VX was compared to those of other commercial solid phase extraction media and was found to be comparable. Sarin was found to be incompatible with both the mixed mode cation exchange (MCX) sorbents and QuEChERS methods that are commercially available but was successful with the normal phase silica gel method. The linear range of quantitation for VX was 0.1-330 ng/mL and for GB was 20-1200 ng/mL. The average recoveries of VX and GB from the various food matrices along with the corresponding relative standard deviations (RSDs) are reported.

Compensation for matrix effects in GC analysis of pesticides by using cucumber extract

Matrix effects (MEs) can adversely affect quantification in pesticide residue analysis using GC. Analyte protectants (APs) can effectively interact with and mask active sites in the GC system, and are added individually or in combination to sample extracts and calibration solutions to minimize errors related to MEs. Unfortunately, APs cannot sufficiently compensate for MEs in all cases. Plant extracts, containing a broad range of natural compounds with AP properties, can also be used for this purpose. In this study, the applicability of cucumber extract as a natural AP mixture was investigated both alone and in combination with traditional APs. Extracts of two selected difficult matrices (onion and garlic) were prepared according to the citrate-buffered QuEChERS (quick, easy, cheap, effective, rugged, and safe) procedure. ME values of 40 representative GC-amenable pesticides were compared when calibrating against standards in pure solvent and in cucumber extract, with and without the addition of APs. Using a GC system with a contaminated inlet liner, the use of a cucumber-based calibration solution decreased MEs remarkably. The combination of APs with cucumber raw extract further decreased MEs, resulting in more than 85% of the tested pesticides showing ≤ 10% ME in onion and ≤ 20% ME in garlic. These results demonstrate that the preparation of calibration standards based on cucumber extracts (with or without the addition of APs) is a very useful and practical approach to compensate for MEs in pesticide residue analysis using QuEChERS and GC-MS/MS. The use of various internal standards is furthermore critically discussed.

Gas chromatography-mass spectrometry determination of polycyclic aromatic hydrocarbons in baby food using QuEChERS combined with low-density solvent dispersive liquid-liquid microextraction

A sensitive GC-MS method is reported for the determination of twelve polycyclic aromatic hydrocarbons (PAHs) in baby food. The sample preparation involves QuEChERS extraction combined with low-density solvent dispersive liquid-liquid microextraction (LDS-DLLME) and ultra-low temperature (-80 °C). Plackett-Burman screening design was employed to identify the main sample preparation variables that affect the extraction efficiency, such as the volume of toluene used in LDS-DLLME. The suitability of proposed method was verified by analytical selectivity, linearity in solvent and matrix-matched calibration curves and adequate recoveries (72-112%) and precision (RSD values ≤11%), under repeatability and within-laboratory reproducibility conditions. High analytical sensitivity was achieved for the monitoring of PAHs at the strict limit of 1 µg kg^-1 fixed by the European Commission for baby foods. The validated method was applied to thirty-two commercial baby food samples, and the investigated PAHs were not detected in any sample.

Rapid and Simultaneous Analysis of 360 Pesticides in Brown Rice, Spinach, Orange, and Potato Using Microbore GC-MS/MS

A multiresidue method for the simultaneous and rapid analysis of 360 pesticides in representative agricultural produce (brown rice, orange, spinach, and potato) was developed using a modified QuEChERS procedure combined with gas chromatography-tandem mass spectrometry (GC-MS/MS). Selected reaction monitoring transition parameters (e.g., collision energy, precursor and product ions) in MS/MS were optimized to achieve the best selectivity and sensitivity for a wide range of GC-amenable pesticides. A short (20 m) microbore (0.18 mm i.d.) column resulted in better signal-to-noise ratio with reduced analysis time than a conventional narrowbore column (30 m × 0.25 mm i.d.). The priming injection dramatically increased peak areas by masking effect on a new GC liner. The limit of quantitation was <0.01 mg/kg, and the correlation coefficients (r²) of matrix-matched standards were >0.99 within the range of 0.0025-0.1 mg/kg. Acetonitrile with 0.1% formic acid without additional buffer salts was used for pesticide extraction, whereas only primary-secondary amine (PSA) was used for dispersive solid phase extraction (dSPE) cleanup, to achieve good recoveries for most of the target analytes. The recoveries ranged from 70 to 120% with relative standard deviations of ≤20% at 0.01 and 0.05 mg/kg spiking levels (n = 6) in all samples, indicating acceptable accuracy and precision of the method. Seventeen real samples from local markets were analyzed by using the optimized method, and 14 pesticides in 11 incurred samples were found at below the maximum residue limits.

Evaluation of pesticide residues of organochlorine in vegetables and fruits in Qatar: statistical analysis

The study aimed to examine the residues of organochlorines pesticides (OCPs) in vegetables and fruits in Qatar. A total of 127 samples was studied. Ninety percent of the imported samples recorded residues above the maximum residue levels (MRLs). The most frequently detected OCP in the samples was heptachlor (found in 75 samples). In the comparisons between the washed and unwashed samples, no significant differences were observed (P > 0.05). However, the effect of washing process with tap water depended on the type of vegetables and fruits.

Determination of matrix effects occurred during the analysis of organochlorine pesticides in agricultural products using GC-ECD

Matrix effects observed during the multiresidue analysis of seven organochlorine pesticides in six different agricultural products with GC-ECD were assessed. The presence of matrix coextractives, a major cause of observed matrix effects, directly and/or indirectly influenced the chromatographic responses of some pesticides. Two types of external calibrations, solvent calibration (SC) and matrixmatched calibration (MC), were used to assess matrix effects. Greater matrix effects were observed at the lower concentrations of each pesticide. The extent of matrix effects varied unpredictably with matrix type. Among the analyzed pesticides, iprodione, cyhalothrin, and cypermethrin exhibited greater matrix effects (>150%) for almost all matrices. The pesticide recovery rates obtained with MC were not statistically different from a 100% recovery rate in most samples, which indicates that MC may diminish the overestimates occurred due to matrix effects in GC analysis.

Injection-port derivatization coupled to GC-MS/MS for the analysis of glycosylated and non-glycosylated polyphenols in fruit samples

Polyphenols, including glycosylated polyphenols, were analyzed via a procedure based on injection-port derivatization coupled to gas chromatography-tandem mass spectrometry (GC-MS/MS). The polyphenols in lyophilized fruit samples were extracted with an acidified MeOH mixture assisted by ultrasound. Samples were dried under vacuum, and carbonyl groups were protected with methoxylamine. Free hydroxyl groups were subsequently silylated in-port. Mass fragmentations of 17 polyphenol and glycosylated polyphenol standards were examined using Multiple Reaction Monitoring (MRM) as the acquisition mode. Furthermore, in-port derivatization was optimized in terms of optimal injection port temperature, derivatization time and sample: N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) volume ratio. A C18 solid-phase-extraction clean-up method was used to reduce matrix effects and injection liner degradation. Using this clean-up method, recoveries for samples spiked at 1 and 10μg/g ranged from 52% to 98%, depending on the chemical compound. Finally, the method was applied to real fruit samples containing the target compounds. The complete chromatographic runtime was 15min, which is faster than reported for recent HPLC methods able to analyze similar compounds.

Enantioseparation and determination of the chiral phenylpyrazole insecticide ethiprole in agricultural and environmental samples and its enantioselective degradation in soil

An effective method for the enantioselective determination of ethiprole enantiomers in agricultural and environmental samples was developed. The effects of solvent extraction, mobile phase and thermodynamic parameters for chiral recognition were fully investigated. Complete enantioseparation of the ethiprole enantiomers was achieved on a Lux Cellulose-2 column. The stereochemical structures of ethiprole enantiomers were also determined, and (R)-(+)-ethiprole was first eluted. The average recoveries were 82.7-104.9% with intra-day RSD of 1.7-8.2% in soil, cucumber, spinach, tomato, apple and peach under optimal conditions. Good linearity (R(2)≥0.9991) was obtained for all the matrix calibration curves within a range of 0.1 to 10 mg L(-1). The limits of detection for both enantiomers were estimated to be 0.008 mg kg(-1) in soil, cucumber, spinach and tomato and 0.012 mg kg(-1) in apple and peach, which were lower than the maximum residue levels established in Japan. The results indicate that the proposed method is convenient and reliable for the enantioselective detection of ethiprole in agricultural and environmental samples. The behavior of ethiprole in soil was studied under field conditions and the enantioselective degradation was observed with enantiomer fraction values varying from 0.494 to 0.884 during the experiment. The (R)-(+)-ethiprole (t1/2=11.6 d) degraded faster than (S)-(-)-ethiprole (t1/2=34.7 d). This report is the first describe a chiral analytical method and enantioselective behavior of ethiprole, and these results should be extremely useful for the risk evaluation of ethiprole in food and environmental safety.

Evaluation of the matrix effect on gas chromatography--mass spectrometry with carrier gas containing ethylene glycol as an analyte protectant

The consequences of matrix effects in GC are a major issue of concern in pesticide residue analysis. The aim of this study was to evaluate the applicability of an analyte protectant generator in pesticide residue analysis using a GC-MS system. The technique is based on continuous introduction of ethylene glycol into the carrier gas. Ethylene glycol as an analyte protectant effectively compensated the matrix effects in agricultural product extracts. All peak intensities were increased by this technique without affecting the GC-MS performance. Calibration curves for ethylene glycol in the GC-MS system with various degrees of pollution were compared and similar response enhancements were observed. This result suggests a convenient multi-residue GC-MS method using an analyte protectant generator instead of the conventional compensation method for matrix-induced response enhancement adding the mixture of analyte protectants into both neat and sample solutions.

Biological Matrix Effects in Quantitative Tandem Mass Spectrometry-Based Analytical Methods: Advancing Biomonitoring

The ability to quantify levels of target analytes in biological samples accurately and precisely in biomonitoring involves the use of highly sensitive and selective instrumentation such as tandem mass spectrometers and a thorough understanding of highly variable matrix effects. Typically, matrix effects are caused by co-eluting matrix components that alter the ionization of target analytes as well as the chromatographic response of target analytes, leading to reduced or increased sensitivity of the analysis. Thus, before the desired accuracy and precision standards of laboratory data are achieved, these effects must be characterized and controlled. Here we present our review and observations of matrix effects encountered during the validation and implementation of tandem mass spectrometry-based analytical methods. We also provide systematic, comprehensive laboratory strategies needed to control challenges posed by matrix effects in order to ensure delivery of the most accurate data for biomonitoring studies assessing exposure to environmental toxicants.

Measurement of macrocyclic trichothecene in floor dust of water-damaged buildings using gas chromatography/tandem mass spectrometry-dust matrix effects

Gas chromatography-tandem mass spectrometry (GC-MS/MS) was used to detect fungal secondary metabolites. Detection of verrucarol, the hydrolysis product of Stachybotrys chartarum macrocyclic trichothecene (MCT), was confounded by matrix effects associated with heterogeneous indoor environmental samples. In this study, we examined the role of dust matrix effects associated with GC-MS/MS to better quantify verrucarol in dust as a measure of total MCT. The efficiency of the internal standard (ISTD, 1,12-dodecanediol), and application of a matrix-matched standard correction method in measuring MCT in floor dust of water-damaged buildings was additionally examined. Compared to verrucarol, ISTD had substantially higher matrix effects in the dust extracts. The results of the ISTD evaluation showed that without ISTD adjustment, there was a 280% ion enhancement in the dust extracts compared to neat solvent. The recovery of verrucarol was 94% when the matrix-matched standard curve without the ISTD was used. Using traditional calibration curves with ISTD adjustment, none of the 21 dust samples collected from water damaged buildings were detectable. In contrast, when the matrix-matched calibration curves without ISTD adjustment were used, 38% of samples were detectable. The study results suggest that floor dust of water-damaged buildings may contain MCT. However, the measured levels of MCT in dust using the GC-MS/MS method could be significantly under- or overestimated, depending on the matrix effects, the inappropriate ISTD, or combination of the two. Our study further shows that the routine application of matrix-matched calibration may prove useful in obtaining accurate measurements of MCT in dust derived from damp indoor environments, while no isotopically labeled verrucarol is available.

Stereoselective degradation of flutriafol and tebuconazole in grape

The stereoselective dissipation of flutriafol and tebuconazole in grape had been studied. A simple and sensitive method for determination of flutriafol and tebuconazole enantiomers in grape was developed by high-performance liquid chromatography on a cellulose tris(3-chloro-4-methylphenylcarbamate) column. The limits of quantification for flutriafol and tebuconazole in grape were 0.033 and 0.043 mg kg(-1), respectively. The dissipations of flutriafol and tebuconazole stereoisomers in grape followed first-order kinetics (R (2) > 0.93). The stereoisomers of flutriafol and tebuconazole were enantioselectively degraded in grape, and tebuconazole was more enantioselective than flutriafol. The half-life of (-)-tebuconazole was 5.2 days and shorter than (+)-tebuconazole with half-life of 6.4 days. The (-)-flutriafol was also preferentially degraded in grape, the half-lives of which were 6.59 and 6.98 days for (-) and (+)-flutriafol, respectively. The enantiomeric ratio value of the two fungicides was nearly 1.0 at the 1st day and increased to 1.143 for flutriafol and 2.015 for tebuconazole at the 28th day. The stereoselective dissipations could provide a reference to fully evaluate the risks of two important chiral triazole fungicides.

Alternative calibration techniques for counteracting the matrix effects in GC-MS-SPE pesticide residue analysis - a statistical approach

This paper investigates the efficiency of application of four different multivariate calibration techniques, namely matrix-matched internal standard (MMIS), matrix-matched external standard (MMES), solvent-only internal standard (SOIS) and solvent-only external standard (SOES) on the detection and quantification of 20 organochlorine compounds from high, low and blank matrix water sample matrices by Gas Chromatography-Mass Spectrometry (GC-MS) coupled to solid phase extraction (SPE). Further statistical testing, using Statistical Package for the Social Science (SPSS) by applying MANOVA, T-tests and Levene's F tests indicates that matrix composition has a more significant effect on the efficiency of the analytical method than the calibration method of choice. Matrix effects are widely described as one of the major sources of errors in GC-MS multiresidue analysis. Descriptive and inferential statistics proved that the matrix-matched internal standard calibration was the best approach to use for samples of varying matrix composition as it produced the most precise average mean recovery of 87% across all matrices tested. The use of an internal standard calibration overall produced more precise total recoveries than external standard calibration, with mean values of 77% and 64% respectively. The internal standard calibration technique produced a particularly high overall standard deviation of 38% at 95% confidence level indicating that it is less robust than the external standard calibration method which had an overall standard error of 32% at 95% confidence level. Overall, the matrix-matched external standard calibration proved to be the best calibration approach for analysis of low matrix samples which consisted of the real sample matrix as it had the most precise recovery of 98% compared to other calibration approaches for the low-matrix samples.

Extraction and GC-MS analysis of phthalate esters in food matrices: a review

According to the Scopus database, using “phthalate” and “GC” as keywords, 758 papers have been found between 1990 and 2014, showing strong and increasing interest in this class of compounds from the scientific community.