Pesticides, pollutants and related compounds

Residues of benomyl [methyl l-(butylcarbamoyl)-2-benzimidazolecarbamate] in soil and in plant tissues may be determined by high-pressure cation-exchange chromatography after conversion of the fungicide into methyl 2-benzimidazolecarbamate (MBC) by acid hydrolysis [56]. 

Method [56,57]. 50 g of sample are extracted with 150 ml of ethyl acetate by blending at high speed for 5-10 min [54]. [Soil samples (50 g) are heated under reflux for 4 h with 17% 1 Af hydrochloric acid in methanol.] After centrifugation, the ethyl acetate is transferred to a 400-ml beaker containing 25 ml of 0.1 N hydrochloric acid. The resulting mixture is heated on a steam bath in a well ventilated fume hood in order to evaporate the ethyl acetate and reduce the final volume to 10-15 ml. (For soils, the acidic methanol 

The aqueous residue is transferred quantitatively to a 2-ml volumetric flask and diluted to the mark with 0.1 TV phosphoric acid. 

Chromatography of MBC is carried out on a strong Zipax CSX cation-exchange column (100 cm X 0.21 cm I.D.). The column is first equilibrated under the following conditions column temperature, 60 °C mobile phase, 0.025 TV tetramethylammonium nitrate-0.02 TV nitric acid flow-rate, 0.5 ml/min. The chromatogram shown in Fig.4.28 is of the analysis of benomyl (as MBC) and 2-aminobenzimidazole (2-AB), a minor metabolite of benomyl, present in cucumber in amounts of 0.05 and 0.1 ppm respectively. The limits of detection are in the range 0.05-0.1 ppm (equivalent to 5-10 ng of benomyl injected). UV detection is made at 254 nm. 

The coupling of HPLC with a cholinesterase-inhibition AutoAnalyzer for the determination of organophosphate and carbamate insecticides has much potential for the routine screening of residues of these compounds [58]. 

---