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

Automated micro-solid-phase extraction clean-up and gas chromatography-tandem mass spectrometry analysis of pesticides in foods extracted with ethyl acetate

Generic extraction methods for the multi-compound pesticide analysis of food have found their solid place in laboratories. Ethyl acetate and acetonitrile extraction methods have been developed as fast and easy to handle standard multi-compound methods, both feature benefits and limitations. The direct injection to gas chromatography can be impaired by a high burden of coextracted matrix, resulting in deterioration of the chromatographic system and matrix effects, requiring frequent maintenance. Therefore, common clean-up methods, such as dispersive solid-phase extraction, freeze-out of fats, or gel permeation chromatography, have been applied in clean-up. Automated clean-up using micro-solid-phase extraction (µSPE) is a recent development with several demonstrated advantages when employed in the analysis of pesticides and other contaminants in foods extracted with acetonitrile, but it has not yet been evaluated in this application using ethyl acetate for extraction. In this study, an automated procedure using µSPE cartridges was developed and established on an x,y,z robotic sampler for the raw extract clean-up and preparation of diluted samples for injection on a GC-MS/MS system. Validation experiments for 212 pesticides, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons in lettuce, avocado, raspberry, paprika, egg, and liver extracts were performed using µSPE with MgSO4, PSA, C18, and CarbonX. The performance in routine operation is briefly discussed.

Dissipation kinetics of co-formulation with two herbicides, clodinafop-propargyl and oxyfluorfen, in/on onion (Allium cepa) samples

Supervised field trail on dissipation of co-formulation with herbicides clodinafop-propargyl and oxyfluorfen in spring onion showed similar pattern of dissipation during two different seasons. Residues of clodinafop-propargyl reached ≤ limit of quantitation (LOQ, 0.05 mg kg^-1) on 3rd day after application at both standard and double dose during both the seasons. Oxyfluorfen residues followed first-order kinetics in both the doses during first season with half-life of 0.81 to 3.14 days. The residues of clodinafop-propargyl were detected in soil at both the doses during first season. However, residues were ≤ LOQ (0.05 mg kg^-1) during second season. The residues of oxyfluorfen were detected only in double dose during first season in soil. In all other cases and in onion bulb, residues were ≤ LOQ (0.05 mg kg^-1) at the time of harvest. As the residues were either ≤ LOQ (0.05 mg kg^-1) on 3rd day or have a half-life of 3.14 days, the co-formulation can be used safely, provided a pre harvest interval (PHI) of 3 days is followed. On the basis of maximum residue limits (MRLs) in other commodities and from the data of present study, a default MRL of 0.05 mg kg^-1 is proposed for both the pesticides.

An aptamer and flower-shaped AuPtRh nanoenzyme-based colorimetric biosensor for the detection of profenofos

A GO grafted SSM was prepared to load the freely mobile capture probe and novel flower-shaped AuPtRh nanospheres were synthesized to be a signal probe, which were constructed to form a colorimetric biosensor for the detection of profenofos.

Facile Detection and Quantification of Acetamiprid Using a Portable Raman Spectrometer Combined with Self-Assembled Gold Nanoparticle Array

Rapid and facile determination of pesticides is critically important in food and environmental monitoring. This study developed a self-assembled gold nanoparticle array based SERS method for highly specific and sensitive detection of acetamiprid, a neonicotinoid pesticide that used to be difficult in SERS analysis due to its low affinity with SERS substrates. SERS detection and quantification of acetamiprid was conducted with self-assembled gold nanoparticle arrays at the interface of chloroform and water as the enhancing substrate. Since targets dissolved in chloroform (organic phase) also have access to the hot-spots of Au NP array, the developed method exhibited good sensitivity and specificity for acetamiprid determination. Under the optimal conditions, SERS intensities at Raman shifts of 631 cm−1 and 1109 cm−1 displayed a good linear relationship with the logarithm concentration of acetamiprid in the range of 5.0 × 10−7 to 1.0 × 10−4 mol/L (0.11335 ppm to 22.67 ppm), with correlation coefficients of 0.97972 and 0.97552, respectively. The calculated LOD and LOQ of this method were 1.19 × 10−7 mol/L (0.265 ppb) and 2.63 × 10−7 mol/L (0.586 ppb), respectively, using SERS signal at 631 cm−1, and 2.95 × 10−7 mol/L (0.657 ppb) and 3.86 × 10−7 mol/L (0.860 ppb) using SERS signal at 1109 cm−1, respectively. Furthermore, the developed SERS method was successfully applied in determining acetamiprid on the surface of apple and spinach. This method offers an exciting opportunity for rapid detection of acetamiprid and other organic pesticides considering its advantages of simple preparation process, good specificity and sensitivity, and short detection time (within 1 h).

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).

Critical review and re-assessment of analyte protectants in gas chromatography

Despite nearly 80 years of advancements in gas chromatography (GC), indirect chemical matrix effects (MEs), known as the matrix-induced response enhancement effect, still occur to cause a high bias in the GC analysis of susceptible analytes, unless precautions are taken. Matrix-matched calibration is one common option used in GC to compensate for the MEs, but this approach is usually inconvenient, imprecise, and inefficient. Other options, such as the method of standard additions, surface deactivation techniques, chemical derivatizations, priming the GC, and/or use of internal standards, also have flaws in practice. When methods are accommodating, the use of analyte protectants (APs) can provide the best practical solution to not only overcome MEs, but also to maximize analyte signal by increasing chromatographic and detection efficiencies for the analytes. APs address the source of MEs in every injection by filling active sites in the GC inlet, column, and detector, particularly in GC-MS, rather than the analytes that would otherwise undergo degradation, peak tailing, and/or diminished response due to interactions with the active sites. The addition of an adequate amount of APs (e.g. sugar derivatives) to all calibration standards and final extracts alike often leads to lower detection limits, better accuracy, narrower peaks, and greater robustness than the other options to compensate for MEs in GC. This article consists of a critical review of the scientific literature, proposal of mechanisms and theory, and re-evaluation studies involving APs for the first time in GC-orbitrap and GC-MS/MS with a high-efficiency ion source design. The findings showed that 1 µg each of co-injected shikimic acid and sorbitol in the former case, and 1 µg shikimic acid alone in the latter case, led to high quality results in multi-residue analysis of pesticides and environmental contaminants.

A modified quick, easy, cheap, effective, rugged, and safe method with hydrophobic natural deep eutectic solvent as extractant and analyte protectant for analyzing pyrethroid residues in tomatoes

In this work, a novel quick, easy, cheap, effective, rugged, and safe technique with hydrophobic natural deep eutectic solvent as both extractant and analyte protectant was developed and combined with gas chromatography-tandem mass spectrometry to analyze pyrethroid residues in tomatoes. Eight hydrophobic natural deep eutectic solvents were first evaluated as analyte protectants and those with decanoic acid or lactic acid as hydrogen bond donor were demonstrated to be effective in compensating for the matrix effects of pyrethroids in the gas chromatography system. Hence, they were added to solvent standards for correcting the quantitation errors instead of matrix-matched calibration standards. Then the abilities of these acid-based deep eutectic solvents to extract pyrethriods from tomatoes were evaluated. Results showed the recoveries of all pyrethroids reached to over 80% with only 5 mL menthol:decanoic acid (1:1) used, and good phase separation was easily achieved without the addition of inorganic salt in the extraction step, indicating hydrophobic natural deep eutectic solvent could be a green substitute for acetonitrile in the quick, easy, cheap, effective, rugged, and safe extraction. Compared with the conventional method, the proposed protocol improved the recoveries, reduced the matrix effects, and simplified the extraction step, demonstrating to be an effective, fast, and green 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.