title: Passive diffusion through polymeric membranes: a novel cleanup procedure for analysis of azinphos-methyl and azinphos-ethyl residues in fruits and vegetables.
abstract: A novel procedure is described for simple removal of coextractives prior to analysis of fruits and vegetables for azinphos-methyl and azinphos-ethyl residues. The solvent extract is concentrated, placed in a polymeric membrane tube, and then dialyzed in cyclohexane. Both azinphos-methyl and azinphos-ethyl diffuse into the surrounding solvent while coextractants remain inside the membrane. The dialyzing solvent is exchanged during concentration with n-hexane and analyzed without further cleanup by gas-liquid chromatography with a specific thermionic detector. The detection limit for a 25 g grape sample with final volume of extract made to 15 mL was 0.01 mg/kg. Recoveries of both residues from grapes averaged 107% (spike levels of 0.3 to 2.0 mg/kg). From a 20 g spinach sample, recoveries averaged 82% for azinphos-methyl and 72% for azinphos-ethyl when final volume of extract was made to 5 mL (spike levels of 0.1 to 1.0 mg/kg). Recoveries from 20 types of fruits and vegetables (20 g sample spiked at 1 mg/kg for both azinphos-methyl and azinphos-ethyl) were consistently greater than 70%, except for strawberries (61-67%) and avocado (28-34%). The high lipid content of avocado may impede diffusion of azinphos-methyl and azinphos-ethyl through the polymeric membrane. A field evaluation of the procedure showed a strong correlation (r = 0.957) between azinphos-methyl residues on grapes and treatments with 2 spray formulations. The membrane cleanup procedure is a simple and cost-effective alternative to other column or liquid-liquid partitioning procedures for azinphos-methyl and azinphos-ethyl residue analysis.
authors.affiliation: New South Wales Department of Agriculture, Biological and Chemical Research Institute, Rydalmere, Australia.
authors.forename: N
authors.initials: N
authors.lastname: Ahmad
authors.forename: L
authors.initials: L
authors.lastname: Guo
authors.forename: P
authors.initials: P
authors.lastname: Mandarakas
authors.forename: S
authors.initials: S
authors.lastname: Appleby
authors.forename: G
authors.initials: G
authors.lastname: Bugueno
mesh_terms: D001387:Azinphosmethyl / Q000031:analogs & derivatives* / Q000032:analysis*; D002849:Chromatography, Gas; D004058:Diffusion; D005506:Food Contamination; D005638:Fruit / Q000737:chemistry; D007306:Insecticides / Q000032:analysis*; D008567:Membranes, Artificial; D010573:Pesticide Residues / Q000032:analysis*; D012995:Solubility; D012997:Solvents; D014675:Vegetables / Q000737:chemistry
chemical_list: D007306:Insecticides; D008567:Membranes, Artificial; D010573:Pesticide Residues; D012997:Solvents; C012762:azinphos ethyl; D001387:Azinphosmethyl