Direct determination of some carbamate pesticides in water and soil by high-performance liquid chromatography

Multiresidue analysis of carbamate pesticides in soil by sonication-assisted extraction in small columns and liquid chromatography

A rapid multiresidue method has been developed for the analysis of carbamate insecticides (oxamyl, methomyl, propoxur, carbofuran, carbaryl and methiocarb) in soil. The method is based on the sonication-assisted extraction of soil samples placed in small columns using a low volume of methanol. Residue levels in soil were determined by reversed-phase high-performance liquid chromatography with fluorescence detection after post-column derivatisation. The separation of carbamates is performed on a C8 column with water-methanol as mobile phase. Recovery studies were carried out at 0.5, 0.1 and 0.01 microg/g fortification levels and average recoveries obtained for carbamates ranged from 82 to 99% with relative standard deviations between 0.4 and 10%. The effect of residue residence time and soil moisture content on the insecticide recovery was also studied. The method is linear over the range assayed, from 0.1 to 1 microg/ml. The detection limit for the carbamates varied from 1.6 to 3.7 microg/kg and the quantification limit obtained was 10 microg/kg. The emission and excitation allowed the confirmation of residues at levels around 0.1 microg/g.

A Fully Automated LC/MS Method Development and Quantification Protocol Targeting 52 Carbamates, Thiocarbamates, and Phenylureas

We have developed a fully automated LC/MS method development and quantification protocol targeting 52 carbamtes, thiocarbamates, and phenylureas. This is a simple LC/MS method with direct injection; no post-column derivatization was required. The method utilized the Waters Alliance HT Chromatography System and the Waters ZQ 2000 mass spectrometer. System control and data processing was by MassLynx 4.0 with QuanLynx Application Manager. Analyte separation was accomplished by Waters Symmetry reversed-phase C8 column. An ammonium acetate water/acetonitrile binary gradient was used for the separation. The MS multichannel ability minimized the LC method development time with less demand on chromatographic peak resolution. Quantification results were obtained for 46 analytes out of the 52 targets. The coefficients of determination ranged from 0.886 to 0.999. The automated LC/MS protocol has sufficient sensitivity to accommodate the current EPA requirements. The limits of detection (3 times the S/N) ranged from 0.091 to 19.3 ng/mL with 50-microL injection. The highly selective MS detector enabled the matrix effect to be minimized. This method was applied to local drinking water and wastewater samples. Each matrix was spiked with the 52 target analytes at 2 and 20 ng/mL. The recoveries were within the EPA acceptance range.

Electrochemical detection of carbamate pesticides at conductive diamond electrodes

Conductive boron-doped diamond thin-film electrodes were used for the electrochemical detection of selected N-methylcarbamate pesticides (carbaryl, carbofuran, methyl 2-benzimidazolecarbamate, bendiocarb) after liquid chromatographic separation. Two kinds of detection methods were adopted in this study. In the first method, a direct detection of underivatized pesticides was carried out at an operating potential of 1.45 V versus Ag/AgCl, which resulted in the detection limits of 5-20 ng/mL (or 5-20 ppb) with S/N = 2 due to the low background current and wide potential window of the diamond electrode. In the second method, the detection limits were improved by subjecting the pesticide samples to alkaline hydrolysis in a separate step prior to injection. The phenolic derivatives obtained by alkaline hydrolysis oxidize at a relatively lower potential (0.9 V vs Ag/AgCl), which increases the sensitivity drastically. The advantage of the diamond electrode for the detection of phenolic derivatives is that it offers excellent stability in comparison to other electrodes. This method gives the detection limits of 0.6-1 ng/mL (or 0.6-1 ppb), which are well below the maximum residue levels allowed for carbaryl, carbofuran, and bendiocarb. While the lowest detection limits (LOD) obtained by the direct detection of pesticides are comparable to the those reported by the well-established HPLC-fluorescence, the LODs of the alkaline hydrolysis method are found to be even lower than the reported limits. On-line reactivation of the diamond electrode surface was shown to be possible by an anodic treatment of the electrode at approximately 3 V for 30 min in case of electrode fouling, which may occur after a prolonged use. Such a treatment damages the glassy carbon (GC) and metal electrodes, while the diamond electrode remains stable. These results suggest that the diamond electrode is superior to the other previously used electrodes such as GC and Kelgraf type for highly sensitive and stable detection of carbamate pesticides.

Accumulation pattern of pesticides in tropical fresh waters

High-performance liquid chromatography has been used to study the persistence of commonly used organophosphorus and carbamate pesticides-carbaryl, carbendazim, carbofuran, dimethoate, malathion and methyl parathion in river water in the presence of bottom sediment in laboratory aquaria. The fate of pesticides in water and sediment in pre- and post-monsoon water from three sources has been compared. It has been established that rapid degradation occurs once the pesticide leaches into sediment from water. Degradation was at a much faster rate in post-monsoon water and sediment. It was found that pH and organic matter content affect rate of decay.

Simultaneous determination of a mixture of organophosphorus and carbamate pesticides by high performance liquid chromatography

A simple HPLC procedure has been developed for the simultaneous determination of a mixture of standard carbaryl, carbofuran, carbendazim, dimethoate, malathion and methyl parathion from a spiked agricultural soil sample. The pesticide mixture has been extracted using methanol-water. A concave gradient elution with acetonitrile-phosphate buffer for 15 min followed by linear elution for 5 min, using a wavelength of 224 nm for detection, has been found to resolve the mixture efficiently.

High-performance liquid chromatographic analysis of carbofuran residues in tomatoes grown in hydroponics

Tomato plants grown in hydroponics were irrigated three times on alternate days with nutrient solutions fortified with carbofuran at levels of 36, 111 and 222 mg 1-1, and carbofuran residues were analysed in tomato fruits. Residues were found to be below the maximum residue level set up by Codex Alimentarius Mundi (0.1 mg kg-1) 6, 11 and 18 days after the third irrigation with nutrient solutions fortified with carbofuran. Consequently, the withholding period of 60 days may be reduced to allow continuous harvest of tomatoes under the conditions used in this experiment.