Photodegradation of Oryzalin in aqueous isopropanol and acetonitrile.

The phototransformation of Oryzalin was studied under UV light (λmax ≥ 290 nm) and sunlight (λmax ≥ 250 nm) in aqueous isopropanol and acetonitrile solution in absence and presence of TiO2 as sensitizer. The rate of photodegradation of Oryzalin in different solvent system followed first-order kinetics, and calculated half-lives were found to be in the range of 23.52-53.75 h for UV light and 41.23-61.43 h for sunlight. From this study, total 12 photoproducts were identified and characterized on the basis of column chromatography and Q-Tof micromass spectral data. The plausible mechanism of phototransformation involved was hydrolysis, breaking of sulfonic bond, and loss of amino and sulfonic acid group.

Photodegradation of hexythiazox in different solvent systems under the influence of ultraviolet light and sunlight in the presence of TiO2, H2O2, and KNO3 and identification of the photometabolites.

The photodegradation of the carboxamide acaricide hexythiazox in three different solvent systems (aqueous methanolic, aqueous isopropanolic, and aqueous acetonitrilic solutions) in the presence of H(2)O(2), KNO(3), and TiO(2) under ultraviolet (UV) light (λ(max) ≥ 250 nm) and sunlight (λ(max) ≥290 nm) has been assessed in this work. The kinetics of photodecomposition of hexythiazox and the identification of photoproducts were carried out using liquid chromatography-mass spectrometry. The rate of photodecomposition of hexythiazox in different solvents followed first-order kinetics in both UV radiation and natural sunlight, and the degradation rates were faster under UV light than under sunlight. Hexythiazox was found to be more efficiently photodegraded in the presence of TiO(2) than in the presence of H(2)O(2) and KNO(3). Two major photoproducts were separated in pure form using column chromatography and identified according to IR, (1)H NMR, and mass spectral information as cyclohexylamine and 5-(4-chlorophenyl)-4-methylthiazolidin-2-one. Another nine photoproducts were identified according to LC-MS/MS spectral information. The plausible photodegradation pathways of hexythiazox were proposed according to the structures of the photoproducts.

Dissipation study of difenoconazole in/on chili fruit and soil in India.

One field experiment was conducted with Difenoconazole (25% EC) on chili crop during December 2009 to January 2010 at two different locations of West Bengal and Maharashtra. The main objective was to understand the residue and persistence behaviour of fungicide difenoconazole in chili fruit and soil samples. Difenoconazole was applied in chili field at 50 mL and 100 mL/100 liter of water. Its residue was analyzed by using LC-MS/MS and it dissipated in chili fruit and soil following first order kinetics. The half life values of difenoconazole were found in the range 2.15-2.32 days and 4.68-8.09 days for chili fruit and soil, respectively.

Dissipation study of thiophanate methyl residue in/on grapes (Vitis vinifera L.) in India.

A multi-location field trial was conducted in India during 2006-2008 to evaluate the dissipation pattern of thiophanate methyl (75% WP) in/on grapes at two application rates (500 and 1,000 g a.i. ha(-1)). The quantitative analysis of the fungicide residues as carbendazim was performed using a UV/VIS spectrophotometer at the maximum absorption band of 281 nm. The average recovery was found 87% and the relative standard deviations (RSD) were below 3.8%. Following the first order kinetics the fungicide dissipates in grapes with a half-life (t(1/2)) value of 4.74-6.52 days irrespective of locations and doses.

Analytical method validation for the determination of meptyldinocap as 2,4-dinitrooctylphenol metabolite in mango and soil using LC-MS/MS and dissipation study of the fungicide in Indian mango field ecosystem.

An analytical method for the quantitative determination of meptyldinocap (2,4-DNOPC) as 2,4-dinitrooctylphenyl (2,4-DNOP) in mango and soil was developed as well as validated using liquid chromatography tandem mass spectrometry (LC-MS/MS). The method comprised an extraction with an acetone:methanol:4 N HCl (100:10:5, v/v/v) mixture followed by hydrolytic conversion of parent 2,4-DNOPC to the corresponding phenol metabolite (2,4-DNOP), and cleanup was done by liquid:liquid partition using ethyl acetate. Final quantitation was performed by LC-MS/MS of 2,4-DNOP with negative electrospray ionization using gradient elution. The method was validated at concentrations ranging from 0.025 to 2 µg/g, and the limit of quantification (LOQ) of meptyldinocap in mango and soil samples was 0.025 µg/g. The recovery of meptyldinocap from mango and soil sample was found to be 93-98% spiked at different levels with analyte, and the relative standard deviation for repeatability (RSD(r)) and reproducibility (RSD(R)) were acceptable (2-6%). The method was rugged as evident from a low measurement uncertainty at 0.05 µg/g. In order to evaluate its safety use in India a multilocational field dissipation study on meptyldinocap in mango was conducted by following the proposed analytical method.

Photodegradation of the herbicide penoxsulam in aqueous methanol and acetonitrile.

Penoxsulam is a triazolopyrimidine sulfonamide group of rice herbicide. The phototransformation of penoxsulam was studied under UV light (lambda max >or= 290 nm) and sunlight in aqueous methanol and acetonitrile solvent system using TiO2 as sensitizer. The rate of photodegradation of penoxsulam in different solvent systems followed first-order kinetics and calculated half-lives was found to be in the range of 51.89-73.41 h and 62.70-97.09 h for UV light and sunlight respectively in the presence or absence of sensitizer. From this study, a total of six photoproducts were identified and characterized on the basis of Q-Tof micromass spectral data. The plausible mechanism of phototransformation involved were hydrolysis, photo oxidation of the sulfonamide group, breaking of sulfonamide bond, loss of amino and sulfonic acid group.