Kresoxim methyl dissipation kinetics and its residue effect on soil extra-cellular and intra-cellular enzymatic activity in four different soils of India.

The rate of degradation of kresoxim methyl and its effect on soil extra-cellular (acid phosphatase, alkaline phosphatase and ß-glucosidase) and intra-cellular (dehydrogenase) enzymes were explored in four different soils of India. In all the tested soils, the degradation rate was faster at the beginning, which slowed down with time indicating a non-linear pattern of degradation. Rate of degradation in black soil was fastest followed by saline, brown and red soils, respectively and followed 1st or 1st + 1st order kinetics with half-life ranging between 1-6 days for natural soil and 1-19 days for sterile soils. The rate of degradation in natural against sterilized soils suggests that microbial degradation might be the major pathway of residue dissipation. Although small changes in enzyme activities were observed, kresoxim methyl did not have any significant deleterious effect on the enzymatic activity of the various test soils in long run. Simple correlation studies between degradation percentage and individual enzyme activities did not establish any significant relationships. The pattern and change of enzyme activity was primarily due to the effect of the incubation period rather than the effect of kresoxim methyl itself.

Adsorption-desorption and leaching behavior of kresoxim-methyl in different soils of India: kinetics and thermodynamic studies.

The sorption and leaching behavior of kresoxim-methyl was explored in four different soils, viz., clay, sandy loam, loamy sand, and sandy loam (saline), representing vegetables and fruits growing regions of India. Adsorption of kresoxim-methyl in all the soils reached equilibrium within 48 h. The rate constants for adsorption and desorption at two different temperatures were obtained from the Lindstrom model, which simultaneously evaluated adsorption and desorption kinetics. The data for rate constants, activation energies, enthalpy of activation, entropy of activation, and free energy indicated physical adsorption of kresoxim-methyl on soil. The relative adsorptivity of the test soils could be attributed to different organic matter and clay contents of the soils. A good fit to the linear and Freundlich isotherms was observed for both adsorption as well as desorption. The groundwater ubiquity score (GUS) for different soils varied between 0 and 2.26. The GUS and leaching study indicated moderately low leaching potential of kresoxim-methyl. The adsorption on four soil types largely depended on the soil physicochemical properties such as organic carbon content, cation-exchange capacity, and texture of the soil.

Dissipation kinetics, safety evaluation, and assessment of pre-harvest interval (PHI) and processing factor for kresoxim methyl residues in grape.

A field dissipation study was conducted to evaluate the pre-harvest interval (PHI) and processing factor (PF) for kresoxim methyl (Ergon 44.3 SC) residues in grapes and during raisin making process at recommended dose (RD) and double the recommended dose (DRD). Kresoxim methyl residues dissipated following 1st-order kinetics with a half-life of 10 and 18 days at RD and DRD, respectively. The PHIs with respect to the European Union maximum residue limit (EU-MRL) of 1 mg kg(-1) for grapes were 13 and 30 days at RD and DRD, respectively. The degradation data during grape to raisin making process were best fitted to nonlinear 1st + 1st-order kinetics with a half-life ranging between 4 and 8 days for both shade drying and with raisin dryer at different doses. The PFs were 1.19 and 1.24 with shade drying and 1.09 and 1.10 with raisin dryer, respectively, which indicates concentration of the residues during raisin making process. The dietary exposure of kresoxim methyl on each sampling day was less than the respective maximum permissible intake both at RD and DRD. The residues of kresoxim methyl in market samples of grapes and raisins were well below the EU-MRL and were also devoid of any risk of acute toxicity related to dietary exposure.

Rapid and sensitive multiresidue analysis of pesticides in tobacco using low pressure and traditional gas chromatography tandem mass spectrometry.

Public exposure to pesticide residues through the main/side-stream smoke of tobacco (Nicotiana tabacum L.) is an international concern. This article reports optimization and validation of large-scale multiresidue analysis methods involving low pressure and traditional gas chromatography tandem mass spectrometry in compliance with the guidance residue levels (GRLs) of Cooperative Centre for Scientific Research Relative to Tobacco (CORESTA). Analysis by low pressure GC-MS/MS offered three times rapid turn around time over the traditional GC-MS/MS with limits of quantifications (LOQs) less than 2µg/L for all the 259 test compounds and the recoveries in the range of 70-118% (±20%) at 10 and 20µg/kg levels of fortification.

Residue analysis of fipronil and difenoconazole in okra by liquid chromatography tandem mass spectrometry and their food safety evaluation.

A liquid chromatography tandem mass spectrometry (LC-MS/MS) based method is reported for simultaneous analysis of fipronil (plus its metabolites) and difenoconazole residues in okra. The sample preparation method involving extraction with ethyl acetate provided 80-107% recoveries for both the pesticides with precision RSD within 4-17% estimated at the limits of quantification (LOQ, fipronil=1ngg(-1), difenoconazole=5ngg(-1)) and higher fortification levels. In field, both the pesticides dissipated with half-life of 2.5days. The estimated pre-harvest intervals (PHI) for fipronil and difenoconazole were 15 and 19.5days, and 4 and 6.5days at single and double dose of field applications, respectively. Decontamination of incurred residues by washing and different cooking treatments was quite efficient in minimizing the residue load of both the chemicals. Okra samples harvested after the estimated PHIs were found safe for human consumption.

Validation of a GC-MS method for the estimation of dithiocarbamate fungicide residues and safety evaluation of mancozeb in fruits and vegetables.

A sensitive and rugged residue analysis method was validated for the estimation of dithiocarbamate fungicides in a variety of fruit and vegetable matrices. The sample preparation method involved reaction of dithiocarbamates with Tin(II) chloride in aqueous HCl. The CS2 produced was absorbed into an isooctane layer and estimated by GC-MS selected ion monitoring. Limit of quantification (LOQ) was ⩽40µgkg(-1) for grape, green chilli, tomato, potato, brinjal, pineapple and chayote and the recoveries were within 75-104% (RSD<15% at LOQ). The method could be satisfactorily applied for analysis of real world samples. Dissipation of mancozeb, the most-used dithiocarbamate fungicide, in field followed first+first order kinetics with pre-harvest intervals of 2 and 4days in brinjal, 7 and 10days in grapes and 0day in chilli at single and double dose of agricultural applications. Cooking practices were effective for removal of mancozeb residues from vegetables.

Optimization of a sample preparation method for multiresidue analysis of pesticides in tobacco by single and multi-dimensional gas chromatography-mass spectrometry.

A selective and sensitive multiresidue analysis method, comprising 4 7pesticides, was developed and validated in tobacco matrix. The optimized sample preparation procedure in combination with gas chromatography mass spectrometry in selected-ion-monitoring (GC-MS/SIM) mode offered limits of detection (LOD) and quantification (LOQ) in the range of 3-5 and 7.5-15ng/g, respectively, with recoveries between 70 and 119% at 50-100ng/g fortifications. In comparison to the modified QuEChERS (Quick-Easy-Cheap-Effective-Rugged-Safe method: 2g tobacco+10ml water+10ml acetonitrile, 30min vortexing, followed by dispersive solid phase extraction cleanup), the method performed better in minimizing matrix co-extractives e.g. nicotine and megastigmatrienone. Ambiguity in analysis due to co-elution of target analytes (e.g. transfluthrin-heptachlor) and with matrix co-extractives (e.g. δ-HCH-neophytadiene, 2,4-DDE-linolenic acid) could be resolved by selective multi-dimensional (MD)GC heart-cuts. The method holds promise in routine analysis owing to noticeable efficiency of 27 samples/person/day.

Optimization of gas chromatography-single quadrupole mass spectrometry conditions for multiresidue analysis of pesticides in grapes in compliance to EU-MRLs.

A single quadrupole GC-MS method was optimized for multiresidue determination of 47 pesticides in grapes with limit of quantifications of each compound in compliance with the EU-MRL requirements. Sample preparation involved extraction of 10 g sample with 10 ml ethyl acetate (+10 g sodium sulphate) by homogenization at 15,000 rpm followed by centrifugation at 3000 rpm. The supernatant was cleaned by dispersive solid phase extraction with primary secondary amine and acidified with 0.1% formic acid. Residues were estimated in selected ion monitoring mode with programmable temperature vaporizer-large volume injection (8 µl). All the GC and MS parameters were thoroughly optimized to achieve satisfactory linearity (R(2)>0.99) within 0.01-0.25 mg kg(-1) with minimum matrix interferences. Recoveries at 0.01 and 0.02 mg kg(-1) were within 67-120% with associated precision RSD below 19%. The method was successfully applied for analysis of the real world samples for incurred residues.

Ensuring selectivity and sensitivity by timed- and ultra-selective reaction monitoring during gas chromatography-tandem mass spectrometric determination of pesticides.

In multiresidue analysis, as the complexity of matrix increases, matrix co-extractives might co-elute and interfere with the detection of target analytes, and thereby result in false positives and erroneous quantifications. This paper aims to evaluate the combination of enhanced mass resolution and concurrent selectivity and sensitivity in analyzing a complex mixture of 341 pesticides in grape, orange, tomato, okra and spinach by gas chromatography triple quadrupole mass spectrometry (GC-MS/MS). Timed-selective reaction monitoring (t-SRM) was found advantageous over segment SRM in terms of ease of method optimization and sensitivity. The optimized t-SRM method was used to test the applicability of ultra-SRM (USRM) in filtering out co-eluting interfering matrix compounds. False detections of benfluralin, dimethoate, etc. could be avoided when mass resolution was increased from 0.7 to 0.4 and 0.2Da (full width at half maximum). Similar observations were noted for chlorobenzilate, spiromesifen, tebuconazole, etc., in grape; omethoate, bendiocarb, monocrotophos, etc. in orange; omethoate, dimethoate, ethoxyquin, atrazine, etc., in tomato; and dichlobenil, omethoate, propoxur, monocrotophos, etc., in okra. The analysis at higher mass resolution could significantly minimize matrix effects (ME), e.g., 34% at 0.7Da for spiroxamine in grape to 0.6% (0.4Da) and -44% (0.7Da) for dichlorvos in okra to 8.8% (0.1Da). A feature called "quantitation enhanced data-dependent (QED) scan feature" was found effective in targeted screening to confirm the detection of atrazine, azoxystrobin, λ-cyhalothrin, etc. at trace quantities in incurred samples and avoid false detection of chlorpyrifos.

Validation of a residue analysis method for streptomycin and tetracycline and their food safety evaluation in pomegranate (Punica granatum L.).

A single-step methanol extraction based method was developed and validated for simultaneous estimation of the residues of streptomycin and tetracycline group compounds in pomegranate fruits by LC-MS/MS. The limits of quantification for all target compounds were ≤0.005 mg kg(-1) with recoveries (%) at fortification levels of 0.005, 0.01, and 0.05 mg kg(-1) being within 90-116% (RSD ≤ 9%) and interday precision RSD ≤ 12% at 0.01 mg kg(-1). A field experiment on the dissipation of streptomycin and tetracycline (including 4-epimers) residues in pomegranate fruits with regards to field applications of the commercial formulation Streptocycline SP (streptomycin sulfate 90% + tetracycline hydrochloride 10%) at 200 and 400 g a.i. ha(-1) indicated preharvest intervals of 45 and 55 days for streptomycin and 12 and 15 days for tetracycline, respectively. The study will be useful in promoting effective residue monitoring and ensuring safe use of these antibiotics in managing bacterial diseases of pomegranate.

Dissipation kinetics of forchlorfenuron, 6-benzyl aminopurine, gibberellic acid and ethephon residues in table grapes (Vitis vinifera).

The residue dynamics of plant growth regulators (PGR) forchlorfenuron (CPPU), 6-benzylaminopurine (6-BA), gibberellic acid (GA3) and ethephon in grape are presented, corresponding to their field applications at recommended and double doses. Random samples were collected from each treated and control plot at regular time intervals. The optimised sample preparation technique involves extraction of 10 g homogenised sample with 20 ml methanol (+1% formic acid) and measurement by LC-MS/MS multiple reaction monitoring, offering limit of quantification ≤0.0025 µg/g for all except ethephon with LOQ of 0.005 µg/g. The recoveries at LOQ and above were 84.8-109.5%. Residue dissipation of all the PGRs followed non-linear two-compartment first+first-order kinetics. CPPU, 6-BA and ethephon residues dissipated with preharvest intervals (PHIs) of 33.5, 12 and 32 days at recommended dose with no PHI applicable for GA3. The PHIs successfully minimised residue problems as observed from survey results of traceable field samples.

Dissipation and distribution behavior of azoxystrobin, carbendazim, and difenoconazole in pomegranate fruits.

The dissipation behavior and degradation kinetics of azoxystrobin, carbendazim, and difenoconazole in pomegranate are reported. Twenty fruits/hectare (5 kg) were collected at random, ensuring sample-to-sample relative standard deviation (RSD) within 20-25%. Each fruit was cut into eight equal portions, and two diagonal pieces per fruit were drawn and combined to constitute the laboratory sample, resulting in RSDs <6% (n = 6). Crushed sample (15 g) was extracted with 10 mL of ethyl acetate (+ 10 g Na(2)SO(4)), cleaned by dispersive solid phase extraction on primary secondary amine (25 mg) and C(18) (25 mg), and measured by liquid chromatography tandem mass spectrometry. The limit of quantification was ≤0.0025 µg g(-1) for all the three fungicides, with calibration linearity in the concentration range of 0.001-0.025 µg mL(-1) (r(2) ≥ 0.999). The recoveries of each chemical were 75-110% at 0.0025, 0.005, and 0.010 µg g(-1) with intralaboratory Horwitz ratio <0.32 at 0.0025 µg g(-1). Variable matrix effects were recorded in different fruit parts viz rind, albedo, membrane, and arils, which could be correlated to their biochemical constituents as evidenced from accurate mass measurements on a Q-ToF LC-MS. The residues of carbendazim and difenoconazole were confined within the outer rind of pomegranate; however, azoxystrobin penetrated into the inner fruit parts. The dissipation of azoxystrobin, carbendazim, and difenoconazole followed first + first order kinetics at both standard and double doses, with preharvest intervals being 9, 60, and 26 days at standard dose. At double dose, the preharvest intervals extended to 20.5, 100, and 60 days, respectively.

Multiresidue analysis of 50 pesticides in grape, pomegranate, and mango by gas chromatography-ion trap mass spectrometry.

A selective and sensitive multiresidue analysis method is reported for simultaneous determination of 50 pesticides of different chemical classes in three commercially important fruits of different nature viz. grape, pomegranate, and mango. The sample preparation method involves extraction of a 10 g sample with 10 mL of ethyl acetate; cleanup by dispersive solid phase extraction with primary secondary amine (PSA, 25 mg) for grape and PSA + graphitized carbon black (25 + 5 mg) for pomegranate and mango; and determination by gas chromatography-ion trap mass spectrometry through multiple reaction monitoring (MRM). Sample preparation under acidified (pH 4) and cold (<4 degrees C) conditions, use of PTV-large volume injection (20 microL) through multibaffled liner and chromatographic separation on a short 10 m VF-5MS capillary column gave a satisfactory response for all of the analytes including relatively unstable compounds such as captan, captafol, folpet, endrine, and iprodione within 31.8 min. The limit of quantification (LOQ) of most of the compounds was

Development and interlaboratory validation of a QuEChERS-based liquid chromatography-tandem mass spectrometry method for multiresidue pesticide analysis.

A high-throughput, QuEChERS (Quick, Easy, Cheap, Effective, Rugged, Safe) sample preparation and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method has been developed and validated for the determination of 191 pesticides in vegetation and fruit samples. Using identical LC analytical column and MS/MS instrumentation and operation parameters, this method was evaluated at the U.S. Food and Drug Administration (FDA), National Research Centre for Grapes (NRCG), India, and Ontario Ministry of the Environment (MOE) laboratories. Method validation results showed that all but 1 of these 191 pesticides can be analyzed by LC-MS/MS with instrument detection limits (IDL) in the parts per trillion (ppt) range. Matrix-dependent IDL studies showed that due to either the low ionization efficiency or matrix effect exerted, 14 of these 191 pesticides could not be analyzed by this method. Method recovery (%R) and method detection limits (MDLs) were determined by the three laboratories using four sample matrices in replicates (N = 4). With >79% of %R data from the fortification studies in the range from 80 to 120%, MDLs were determined in the low parts per billion range with >94% of MDLs in the range from 0.5 to 5 ppb. Applying this method to the analysis of incurred samples showed that two multiple reaction monitoring (MRM) transitions may not be enough to provide 100% true positive identification of target pesticides; however, quantitative results obtained from the three laboratories had an excellent match with only a few discrepancies in the low parts per billion levels. The %R data from the fortification studies were subjected to principal component analysis and showed the majority of %R fell into the cluster of 80% < %R < 120%. Due to the matrix effect exerted by ginseng and peach, outliers were observed at the lowest spiking levels of 10 and 25 ppb. The study also showed that QuEChERS samples should be analyzed as soon as prepared or stored in a freezer to avoid any adverse affect on the analytes evaluated.