Pesticide standards, carbamate

Leon-Gonzalez, M.E., and Townshend, A. (1991) Determination of organophosphorus and carbamate pesticide standards by liquid chromatography with detection by inhibition of immobilized acetylcholinesterase, J. Chromatogr. 539, 47-54. 

Obtain organochlorine and carbamate pesticide standards from a commercial source such as Polyscience Corp. or ChemService (Westchester, PA). Obtain standards of phorate and its metabolites from the manufacturer, American Cya-namid Co., Princeton, NJ. Prepare individual and mixture solutions at a level of 1 J,g/)il by dissolving 25 mg of each compound in 25 ml of solvent. For the study of chlorinated pesticides, prepare individual solutions and a mixture of heptachlor, endosulfan (Thiodan), heptachlor epoxide, lindane, dieldrin, and dico-fol (Kelthane) in hexane. For organophosphate pesticides, use phorate and its metabolites phoratoxon, phorate sulfoxide, and phoratoxon sulfoxide in ethyl acetate. For carbamates, use 3-keto carbofuran (a metabolite of carbofuran), carbaryl, and metalkamate (Bux) in ethyl acetate. 

Meier, E.R, M.C. Warner, W.H. Dennis, W.F. Randall, and T.A. Miller. 1976. Chemical Degradation of Military Standard Formulations of Organophosphate and Carbamate Pesticides. I. Chemical Hydrolysis of Diazinon. U.S. Army Med. Bioengin. Res. Dev. Lab., Fort Detrick, Frederick, MD. Tech. Rep. 7611. 32 pp. 

Materials. Aldicarb standards were obtained from the United States Environmental Protection Agency (USEPA), Quality Assurance Section and from Union Carbide Corporation. Crystalline samples of carbofuran and 3-hydroxycarbofuran were supplied by the Agricultural Chemical Group of FMC Corporation. Reference standards of methomyl (99% pure) and oxamyl (99% pure) were obtained from USEPA. HPLC grade methanol was purchased from Burdick and Jackson, Inc. Methylene chloride used for bulk extractions of the carbamate pesticides in solution was recovered, distilled and reused. Analytical reagent grade chemicals and solvents were used in all experiments. Doubly distilled deionized water was used for solution rate studies. Deionized distilled water (DDW) was used for dilutions in reactive ion exchange experim ts., , ... 

Thiocholine was studied first as a standard thiol compound because of its importance in environmental analysis. Determination of thiocholine is in fact usually carried out to evaluate the degree of inhibition of acetylcholinesterase, a target enzyme of pesticides, as a means for indirect measurements of organophosphorous and carbamate pesticides. 

Most SPME applications involve GC. Following extraction, the analytes are thermally desorbed in the chromatograph injector. More recently, the scope of apphcation has been extended to nonvolatile and thermally unstable compounds by coupling SPME to LC. Desorption is performed at an appropriate interface consisting of a standard six-way HPLC injector with a special fiber-desorption chamber used instead of the sample loop. A different approach to SPME-LC called in-tube SPME has also been developed, it uses an open tubular fused-silica capillary column instead of the typical SPME fiber. This latter method has been used for the determination of carbamate pesticides in water with relative standard deviations of... 

OP), and carbamate pesticides are available as standard methods by the AO AC covering both nonfatty and fatty foods. These methods are based on solvent extraction and a variety of column chromatographic cleanup procedures with determination by GC using selective detectors. The International Dairy Federation has approved similar methods for OC and OP pesticide residues in milk and milk products. The AOAC have standard methods for specific pesticides or groups of pesticides that are approved for certain foodstuffs these methods involve colorimetric, spectrophotometric, or gas chromatographic determination. In the case of me-thylcarbamate pesticides, a liquid chromatographic method is approved. 

The insecticide carbaryl (1-naphthyl-A-methylcarbamate, Figure 7.4) has been measured on filter paper exposed during aerial spraying using an ODS-modified silica column and ED (GCE, +0.75 V vs Ag/AgCl) after pre-column alkaline hydrolysis to 1-naphthol. The eluent was acetonitrile-acetic acid-aq. potassium chloride (0.5 mol L ) (50 + 1 + 49). 2-Naphthol was the internal standard. Postcolumn hydrolysis with sodium hydroxide of carbaryl and some other A -methyl-carbamate pesticides has also been employed in measuring crop residues of these compounds. The analytical column used was octyl-modified silica. Elution was... 

The anticholinesterase inhibitors (organophosphorous and carbamate), have come into widespread use in the last decades, because they are less persistent in the environment than other pesticides, such as organochlorine. However their presence in water and food is a potential hazard to human health and there is a growing interest in their rapid and accurate determination. Standard methods, based on gas chromatography (GC), are very reliable but there is the need for fast and innovative methods. The use of enzymatic biosensors, and especially electrochemical biosensors, for organophosphorus and carbamate pesticides detection has been reported by many authors [22-26]. 

Methyl 5-hydroxy-2-benzimidazole carbamate (MHBC, Figure 7.4), a urinary metabolite of the pesticides carbendazium, benomyl and thiophanate-methyl, has been measured using an ODS-modihed silica analytical column with methanol-aq. ammonium acetate (approximately 60 mmol L , pH 8) (27 + 73) as eluent and ED (PGE, +0.22 V vs Pd). Sample preparation was by a complex procedure involving SPE (SCX-modified silica) of hydrolysed specimens. No internal standard... 

DDT), organophosphorus (chloipyrifos), and carbamate (carbaryl) pesticides. The lowest limit of detection (LOD) was obtained for DDT with 20 ng 1 , while 50 ng 1 and 0.9 pg 1 were achieved for chloipyrifos and carbaryl, respectively. Matrix effects were evaluated for the carbaryl immunoassay in different water t3tpes with detection limits within the range of carbaryl standards in distilled water (0.9-1.4 pg 1 ). This portable SPR-sensor system is already a product on the market, commercialized by the company SENSIA, SL (Spain). The size and the electronic configuration of the device allow its portabihty and utilization at contaminated locations. ... 

---