Sulfur-containing pesticides, detection

Another spray reagent used by Belliveau and Frei (25) after treatment of the chromatogram with bromine vapours, is 1,2-dichloro-4,5-dicyanobenzoquinone (DDQ). This compound was used to detect a large number of sulfur-containing pesticides. Unfortunately the reagent is sensitive to light which causes... 

The non-polar chlorinated hydrocarbon pesticides are routinely quantified using gas chromatography (GC) and electron capture(EC) detection. Alternate detectors include electrolytic conductivity and microcoulometric systems. Organophosphate pesticides which are amenable to GC are responsive to either the flame photometric detector (FPD) or the alkali flame detector (AFD). Sulfur containing compounds respond in the electrolytic conductivity or flame photometric detectors. Nitrogen containing pesticides or metabolites are generally detected with alkali flame or electrolytic conductivity detectors. 

The flame photometric detector (FPD) is a mass-sensitive detector, which is speciflc for sulfur and phosphorous. The light that is emitted from phosphorus or sulfur combustion products is measured. The detection limit is about 5 pg S s and 50-100 pg P s and the linearity is 10 -10". Main area of use is speciflc detection of sulfur in petroleum and petrochemical samples as well as of phosphorus containing pesticides. 

Most sulfur-containing compounds can be detected by UV-vis. Pico et al. [2] analyzed pesticides using low-wavelength UV detection in water. 

Carbamate pesticides can be determined using different detectors in GC or HPLC analysis. A characteristic feature of a carbamate molecule is the nitrogen atom, which can form the bases for quantitation and some carbamates also contain chlorine, sulfur, or other heteroatoms in the molecule. This allows the use of various detection techniques for their determination (139,140), such as electrical conductivity (165), alkali flame (141) photometry, and mass spectrometry (44,166). 

Benomyl absorbed by plants is rapidly metabolised in the tissue fluids into MBC (Sims et al., 1969 Peterson and Edgington, 1970), so that benomyl itself can be detected only rarely in the tissue fluids. Sunlight, heat and various solvents enhance the transformation. At the same time, Baude et al. (1973) showed by the chemical approach that benomyl has adequate stability in aqueous suspensions at a concentration usual in sprays. An aqueous suspension of the benomyl preparation Benlate at 23°C contained more than 90% of the original benomyl even after 48 hours. After a longer time, the larger part of the residue found on the leaves consisted of intact benomyl. No other metabolites were found in the plant in addition to MBC, even if benomyl was used in combination with alkaline pesticides (basic copper sulfate or lime sulfur solution) in the spray. Thus, because of its low solubility, the hydrolysis of benomyl in practice is not as rapid as has been measured in dilute solutions by several authors (Jhooty and Singh, 1972 Brown and Albrigo,... 

The popularity of the BCD can be attributed to the high sensitivity to organohalogen compounds, which include many compounds of environmental interest, including polychlorinated biphenyls and pesticides. It is the least selective of the so-called selective detectors but has the highest sensitivity of any contemporary detector. The NPD or thermionic ionization or emission detector is a modified FID in which a constant supply of an alkali metal salt, such as rubidium chloride, is introduced into the flame. It is a detector of choice for analysis of organophosphorus pesticides and pharmaceuticals. The FPD detects specific luminescent emission originating from various excited state species produced in a flame by sulfur- and phosphorus-containing compounds. 

Carbaiyl, bendiocaib, carbofiiran. baygmi, ziram, zineb, and aldicaib were separated on silica gel G layers impregnated with Vh zinc acetate. Zinc sulfate, cadmium acetate, and ntanganese acetate were studied as impregnants, but the best resolution was observed on the above-mentioned zinc acetate-containing suppcxt /fy values are summarized in Table 4. The detection of these pesticides was carried out by cesium sulfate in 60% sulfuric acid solution (67). 

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