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 synthetic pyrethroid pesticides in grapes by gas chromatography with programmed temperature vaporizing-large volume injection coupled with ion trap mass spectrometry.

A multiresidue analysis method was optimized and validated for simultaneous estimation of 21 synthetic pyrethroid pesticides and their isomers in grape matrix at 10 ng/g and higher levels. The method involves extraction of a 10 g sample with 10 mL ethyl acetate, cleanup by dispersive SPE with primary-secondary amine (25 mg) sorbent, and estimation by GC/MS/MS large volume injection (LVI) through a programmed temperature vaporizer (PTV) injector. The PTV-LVI parameters of the gas chromatograph and the multiple reaction monitoring (MRM) parameters of the ion trap mass spectrometer were optimized for each compound to achieve the highest SIN. For each analyte, the unique and most abundant MRM transition was used for quantification, along with the next most abundant MRM transition for confirmatory identification. The abundance ratio of the confirmatory to quantifier MRMs was used to ensure unambiguous residue monitoring in unknown samples within a 20% tolerance range at the 10 ng/g level. The analytes were separated on a TR-5MS capillary column within a 22 min run time. The method was selective and sensitive and ensured separation of the synthetic pyrethroids from high-boiling matrix components. The LOD and LOQ of the analytes ranged between 0.5 to 3.1 and 2.5 to 10 ng/g, respectively. Linearity of solvent and matrix-matched calibrations between 2.0 and 250 ng/g was established for each compound with r2 > 0.99. Recovery at 10, 25, and 50 ng/g levels of fortification in grapes ranged within 77-115% with associated RSD values (n = 8) up to 20%.

Optimization of two-dimensional gas chromatography time-of-flight mass spectrometry for separation and estimation of the residues of 160 pesticides and 25 persistent organic pollutants in grape and wine.

Two-dimensional gas chromatography (GCxGC) coupled with time-of-flight mass spectrometric (TOFMS) method was optimized for simultaneous analysis of 160 pesticides, 12 dioxin-like polychlorinated biphenyls (PCBs), 12 polyaromatic hydrocarbons (PAHs) and bisphenol A in grape and wine. GCxGC-TOFMS could separate all the 185 analytes within 38min with >85% NIST library-based mass spectral confirmations. The matrix effect quantified as the ratio of the slope of matrix-matched to solvent calibrations was within 0.5-1.5 for most analytes. LOQ of most of the analytes was < or =10microg/L with nine exceptions having LOQs of 12.5-25microg/L. Recoveries ranged between 70 and 120% with <20% expanded uncertainties for 151 and 148 compounds in grape and wine, respectively, with intra-laboratory Horwitz ratio <0.2 for all analytes. The method was evaluated in the incurred grape samples where residues of cypermethrin, permethrin, chlorpyriphos, metalaxyl and etophenprox were detected at below MRL.

Ultrasound-assisted emulsification microextraction for determination of 2,4,6-trichloroanisole in wine samples by gas chromatography tandem mass spectrometry.

A fast and effective microextraction technique is proposed for preconcentration of 2,4,6-trichloroanisole (2,4,6-TCA) from wine samples prior gas chromatography tandem mass spectrometric (GC-MS/MS) analysis. The proposed technique is based on ultrasonication (US) for favoring the emulsification phenomenon during the extraction stage. Several variables influencing the relative response of the target analyte were studied and optimized. Under optimal experimental conditions, 2,4,6-TCA was quantitatively extracted achieving enhancement factors (EF) > or = 400 and limits of detection (LODs) 0.6-0.7 ng L(-1) with relative standard deviations (RSDs) < or = 11.3%, when 10 ng L(-1) 2,4,6-TCA standard-wine sample blend was analyzed. The calibration graphs for white and red wine were linear within the range of 5-1000 ng L(-1), and estimation coefficients (r(2)) were > or = 0.9995. Validation of the methodology was carried out by standard addition method at two concentrations (10 and 50 ng L(-1)) achieving recoveries >80% indicating satisfactory robustness of the method. The methodology was successfully applied for determination of 2,4,6-TCA in different wine samples.

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

Multiresidue determination and uncertainty analysis of 87 pesticides in mango by liquid chromatography-tandem mass spectrometry.

A liquid chromatography-tandem mass spectrometry (LC-MS/MS)-based method was optimized and validated for the multiresidue analysis of 87 pesticides in mango at the ≤ 10 ng g(-1) level. The method involves extraction of 10 g of homogenized mango samples (+10 mL of water + 1 g of sodium acetate + 10 g of sodium sulfate) with 10 mL of ethyl acetate; cleanup by dispersive solid-phase extraction with a combination of primary secondary amine (PSA, 50 mg), graphitized carbon black (GCB, 25 mg), and anhydrous sodium sulfate (150 mg); and final estimation by LC-MS/MS with multiple reaction monitoring. Direct analysis (no clean up) resulted in significant suppression in ionization of the majority of the test compounds over the electrospray ionization probe. However, clean up with the above combination of PSA + GCB reduced the matrix-induced signal suppressions significantly, and the signals in the cleaned extracts were nearly equivalent to the corresponding solvent standards. Substitution of PSA with florisil also gave equivalent clean up effects. The method was quite rugged as evident from a low Horwitz ratio (mostly <0.5) and low measurement uncertainties at 10 ng g(-1). The limit of quantification was <10 ng g(-1) for all of the pesticides with recoveries within 70-120% for most pesticides even at 2.5 ng g(-1). The method offers a significantly effective, sensitive, cheaper, and safer alternative to the existing methods of multiresidue analysis.

Multiresidue analysis of 83 pesticides and 12 dioxin-like polychlorinated biphenyls in wine by gas chromatography-time-of-flight mass spectrometry.

A multiresidue method is described for simultaneous estimation of 83 pesticides and 12 dioxin-like polychlorinated biphenyls (PCBs) in red and white wines. The samples (20mL wine, acidified with 20 mL 1% HCl) were extracted with 10 mL ethyl acetate (+20 g sodium sulphate) and cleaned by dispersive solid-phase extraction (DSPE) with anhydrous calcium chloride and Florisil successively. The final extract (5 mL) was solvent exchanged to 1mL of cyclohexane:ethyl acetate (9:1), further cleaned by DSPE with 25mg primary secondary amine sorbent and analyzed by gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS) within 31 min run time. The limits of quantification of most analytes were 80% for most analytes except cyprodinil, buprofezin and iprodione. The expanded uncertainties at 10 ng/mL were <20% for most analytes. Intra-laboratory precision in terms of Horwitz ratio of all the analytes was below 0.5, suggesting ruggedness of the method. Effectively, the method detection limit for most analytes was as low as up to 1 ng/mL in both red and white wine, except for cyfluthrin and cypermethrin.

Degradation kinetics and safety evaluation of buprofezin residues in grape (Vitis vinifera L.) and three different soils of India.

BACKGROUND: This work was undertaken to determine the preharvest interval (PHI) of buprofezin to minimize its residues in grapes and thereby ensure consumer safety and avoid possible non-compliance in terms of residue violations in export markets. Furthermore, the residue dynamics in three grapevine soils of India was explored to assess its environmental safety. RESULTS: Residues dissipated following non-linear two-compartment first + first-order kinetics. In grapes, the PHI was 31 days at both treatments (312.5 and 625 g a.i. ha(-1)), with the residues below the maximum permissible intake even 1 h after foliar spraying. Random sampling of 5 kg comprising small bunchlets (8-10 berries) collected from a 1 ha area gave satisfactory homogeneity and representation of the population. A survey on the samples harvested after the PHI from supervised vineyards that received treatment at the recommended dose showed residues below the maximum residue limit (MRL) of 0.02 mg kg(-1) applicable for the European Union. In soil, the degradation rate was fastest in clay soil, followed by sandy loam and silty clay, with a half-life within 16 days in all the soils. CONCLUSION: The recommendation of the PHI proved to be effective in minimizing buprofezin residues in grapes. Thus, this work is of high practical significance to the domestic and export grape industry of India to ensure safety compliance in respect of buprofezin residues, keeping in view the requirements of international trade.

Degradation kinetics of forchlorfenuron in typical grapevine soils of India and its influence on specific soil enzyme activities.

The rate of degradation of forchlorfenuron, a cytokinin-based plant growth regulator (PGR) was explored in typical grapevine soils of India with simultaneous evaluation of its effect on biochemical attributes of the test soils in terms of the activities of specific soil microbial enzymes. In all the test soils, namely clay, sandy-loam and silty-clay, the dissipation rate was faster at the beginning, which slowed down with time, indicating a non-linear pattern of degradation. Degradation in soils could best be explained by two-compartment 1st+1st order kinetics with half-life ranging between 4-10 days. The results suggest that organic matter might be playing a major role in influencing the rate of degradation of forchlorfenuron in soil. The rate of degradation in sandy-loam soil was fastest followed by clay and silty-clay soils, respectively. Comparison of the rate of degradation in natural against sterilized soils suggests that microbial degradation might be the major pathway of residue dissipation. Changes in soil enzyme activities as a consequence of forchlorfenuron treatment were studied for extra-cellular enzymes namely acid phosphatase, alkaline phosphatase and beta -glucosidase and intracellular enzyme-dehydrogenase. Although small changes in enzyme activities were observed, forchlorfenuron did not have any significant deleterious effect on the enzymatic activity of the test soils. 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 the effect of the incubation period rather than the effect of forchlorfenuron itself.

Optimization of separation and detection conditions for the multiresidue analysis of pesticides in grapes by comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry.

A comprehensive GCxGC-TOFMS method was optimized for multiresidue analysis of pesticides using a combination of a non-polar (RTX-5MS, 10 m x 0.18 mm x 0.2 microm) and a polar capillary column (TR-50MS, 1 m x 0.1 mm x 0.1 microm), connected in series through a dual stage thermal modulator. The method resolved the co-elution problems as observed in full scan one-dimensional GC-MS analysis and allowed chromatographic separation of 51 pesticides within 24 min run time with library-searchable mass spectrometric confirmation. Four pesticides, viz. chlorpyrifos-methyl, vinclozoline, parathion-methyl and heptachlor could be baseline separated on GCxGC, which were otherwise closely eluting and interfering each other's detection in 1D GC-MS run. Similarly, it could be possible to separate myclobutanil, buprofezin, flusilazole and oxyfluorfen on GCxGC. Although in 1D GC-MS, these closely eluting compounds could be identified through deconvolution algorithm and 'peak-find' option of the Chromatof software but the spectral purity significantly improved on GCxGC analysis. Thorough optimization was accomplished for the oven temperature programming, ion source temperature and GCxGC parameters like modulation period, duration of hot pulses, modulation-offset temperature, acquisition rate, etc. to achieve best possible separation of the test compounds. The limit of detection significantly improved by 2-12 times on GCxGC-TOFMS against GC-TOFMS because of sharper and narrower peak shapes. The method was tested for grape matrix after preparing the samples using previously described method and recoveries of the entire test pesticides were within 70-110% at 10 ng/g level of fortification. GCxGC-TOFMS was found to be an excellent technique for library-based screening of pesticides with high accuracy and sensitivity.

Sorption of thiamethoxam in three Indian soils.

The sorption behavior of the insecticide thiamethoxam [3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro)amine] on three Indian soils with different physico-chemical properties was investigated. The soils represent the major grapevine growing areas of India, where the vineyards frequently receive thiamethoxam applications as foliar spray, soil drenching and through drip irrigation for the management of various insect pests. 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 thiamethoxam on soil. The adsorptivity of different soils might be attributed to the organic matter and clay contents. A good fit to the linear and Freundlich isotherms was observed for both adsorption as well as desorption. Thiamethoxam could be categorized as a chemical with medium leaching potential.

Degradation kinetics and safety evaluation of tetraconazole and difenoconazole residues in grape.

BACKGROUND: Tetraconazole and difenoconazole are triazole fungicides with proven bioefficacy against grapevine powdery mildew disease. In the present work, the authors explored the residue dynamics of these two compounds in grapes and determined their preharvest intervals (PHIs) corresponding to multiple field applications at recommended and double rates considering the most critical use pattern in Indian viticulture. A confirmatory residue analysis method was validated for trace-level determination of both the compounds. RESULTS: Dissipation of both the fungicides followed non-linear two-compartment first + first-order rate kinetics. Tetraconazole and difenoconazole dissipated with PHIs of 12.5 and 25.5 days at recommended rates and of 28.5 and 38.5 days at double application rates respectively. On all the sampling days, the residues were below the maximum permissible intake, indicating consumer safety. The residues in the grape samples drawn from the farms where these two fungicides were applied, maintaining the above PHIs, were below their respective MRLs. CONCLUSION: The rate of degradation of tetraconazole was faster than that of difenoconazole. Thus, the growers will have the choice of using these new chemicals for the management of powdery mildews in succession, difenoconazole at early growth stages, followed by tetraconazole during the last month before harvest. The recommendations of PHIs proved to be effective in minimizing residues in farm grape samples. Thus, this work is of high significance to the grape industry of India, and will support the registration of these new fungicides for effective management of powdery mildews with minimum residue problems.

Sorption behaviour of forchlorfenuron in soil.

Adsorption of forchlorfenuron on three Indian soils reached equilibrium within 48 h with rate of adsorption being highest on sandy-loam followed by clay and silty-clay soils. The relative adsorptivity of the test soils could be attributed to the different organic matter and clay contents. Desorption rate followed the reverse trend. The rate constants for adsorption and desorption at 298 and 308 K were determined from 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 chemical adsorption of forchlorfenuron on soil. A good fit to the linear and Freundlich isotherms was observed with correlation coefficients >0.97. The groundwater ubiquity score for different soils varied between 1.6 and 2.2, on the basis of which forchlorfenuron could be categorised as a chemical with low to medium leaching category.

Single-laboratory validation and uncertainty analysis of 82 pesticides determined in pomegranate, apple, and orange by ethyl acetate extraction and liquid chromatography/tandem mass spectrometry.

Single-laboratory validation results are reported for the multiresidue determination of 82 pesticides at < or = 10 ng/g levels in pomegranate, apple, and orange. Samples were extracted with ethyl acetate, and the extracts were cleaned up by dispersive solid-phase extraction with primary secondary amine sorbent. The concentrations of the pesticides were estimated within 18 min of chromatographic run time by liquid chromatography/mass spectrometry with multiple-reaction monitoring. The method was reproducible (HorRat of < 0.5 at 10 ng/g) with measurement uncertainties of < 15% for all the compounds at 10 nglg in all 3 matrixes. The limits of quantitation ranged from 2.5 to 5.0 ng/g with recoveries of 70-120% for most pesticides. Matrix-induced signal suppressions were significantly higher in orange compared with those in pomegranate and apple. The method offers a less expensive and safer alternative to the existing multiresidue analysis methods for fruits and vegetables.

Validation and uncertainty analysis of a multi-residue method for pesticides in grapes using ethyl acetate extraction and liquid chromatography-tandem mass spectrometry.

A method was validated for the multi-residue analysis of 82 pesticides in grapes at

Rate of degradation of lambda-cyhalothrin and methomyl in grapes (Vitis vinifera L.).

Rates of degradation of lambda-cyhalothrin and methomyl residues in grape are reported. The dissipation behavior of both insecticides followed first-order rate kinetics with similar patterns at standard and double-dose applications. Residues of lambda-cyhalothrin were lost with pre-harvest intervals (PHI) of 12.0-12.5 and 15.0-15.5 days, corresponding to the applications at 25 and 50 g a.i. ha-1, respectively. In the case of methomyl, residues were lost with PHI of 55.0 and 61.0 days, following applications at 1 and 2 kg a.i. ha-1, respectively. The PHI, recommended on the basis of the experimental results, was shown to be effective in minimizing residue load of these insecticides below their maximum residue limits (MRLs) in vineyard samples.