The study was conducted to investigate matrix interferences using QuEChERS sample preparation to understand whether the dilution of matrix and/or the grouping of commodities can eliminate the need for selective individual matrix-matched standards in LC with tandem MS (MS/MS) analysis, and whether the calibration graph based on only one matrix can be used for quantification in the other matrixes. Matrix effects (MEs) were studied by comparing the slopes of calibration curves of the matrix-matched standards (diluted with mobile phase) vis-à-vis the solvent-based standards. The present study showed that MEs were dependent on the nature of both the commodity and the analyte. Among the test matrixes, the highest variability in ME was recorded in capsicum. Most of the pesticides showed signal suppression in tomato, capsicum, and cumin matrixes. In brinjal matrix, the signal of most of the pesticides showed slight enhancement. Due to the similar nature of the MEs in tomato and capsicum, these two commodities can be grouped together. Considering analyte variability, acetamiprid, 3-hydroxy carbofuran, dichlorvos, dimethoate, and spinosyn A and D showed no significant ME (≤20%) in tomato. Very high MEs (2360.9 and 1250.8%) were observed for quizalofop-p-tefuryl and tebuconazole, respectively. To check the effect of dilution in minimizing the ME, cucumber and brinjal matrixes were diluted 10×, and calibration curves were drawn with five concentration levels. It was found that about 60% of the total analyzed pesticides showed MEs ≤20%. In cumin, MEs ranged from -5.3% for triazophos to 661% for thiacloprid. Most of the pesticides showed recoveries in the acceptable range of 70-130% with calibration curves from both matrixes. To compensate for MEs, it is suggested that (1) tomato and capsicum matrixes, which show similar trends, can be grouped together; and (2) cucumber matrix, when diluted 10×, can be used to prepare calibration curves for the quantification of pesticides in various fruiting and cucurbit vegetable matrixes by LC-MS/MS.
A method was validated for estimating fluopyram and tebuconazole in onion on LC-MS/MS using dispersive QuEChERS. Three sprays of a combination fungicide fluopyram + tebuconazole (Luna experience, 400 SC) were applied @ 75 + 75 and 150 + 150 g a.i. ha at an interval of 10 days on onion using Knapsack sprayer. First spray was made at bulb setting stage. Spring onion samples were drawn at 0 (1 h), 1, 3, 5, 7, 10, 15, and 20 days and matured onion bulb at harvest (52 days) after the last spray. Soil samples were also drawn at harvest. Foliar application of the combination product resulted in 1.14 and 2.86 mg kg fluopyram residues on spring onion at standard and double dose, respectively, one hour after the last application. The levels of fluopyram residues gradually declined and recorded 0.25 and 0.58 mg kg on 20th day of application with half-lives of 8.8 and 9.1 days at standard and double dose, respectively. For tebuconazole, the corresponding residues observed after 1 h (0 day) of application were 0.92 and 2.29 mg kg. The levels declined gradually to 0.12 and 0.33 mg kg on 20th days with half-life of 6.7 to 7.7 days at standard and double dose, respectively. Here, we are proposing a pre-harvest interval of 7 day for fluopyram and tebuconazole in spring onion when applied at 75 + 75 g a.i. ha (400 SC). Risk assessment was done by calculating hazard quotient and by comparing theoretical maximum residue intake (TMRI) with maximum permissible intake (MPI). In all the cases, results of the study showed that HQ (Hazard Quotient) ≤1 and TMDI < MPI. Hence, the use of this combination product can be recommended with pre harvest interval of 7 days. The data can be used in establishing MRLs (maximum residue limits) for spring onion after considering multilocation trials.
A method was developed and validated for the analysis of 87 pesticides in cotton and groundnut oil by GC with ECD and FPD detectors and LC-MS/MS. The extraction procedure based on QuEChERS followed by low-temperature freezing and dispersive cleanup steps was validated in two oil matrices for 87 pesticides of different classes. Linearity, expressed as coefficient of variation, was within the acceptable range. Of those tested, 77-83 and 77-89% pesticides showed recoveries within the acceptable range of 70-120% on LC-MS/MS in cottonseed oil and groundnut oil, respectively, at different spiking levels. In case of GC analysis, 63-65 and 53-82% pesticides showed recoveries within the acceptable range of 70-120% on GC in cottonseed oil and groundnut oil, respectively, at different spiking levels. The exceptions to these recoveries were the few organochlorines which consistently gave lower recoveries. Recovery factors can be employed while analysing these pesticides by this method as the results obtained were consistent in both oils. RSD was less than 20% for most of the pesticides. The calculated limit of quantitation (LOQ) for most of the pesticides satisfies the maximum residue level (MRL) requirements as per European Union (EU) guidelines and Food Safety and Standards Authority of India (FSSAI).
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