Analytical methods
Fruit and vegetables. The Netherlands submitted a qualitative multi-residue TLC method which allows the determination of the (E)- and (Z)- isomers of chlorfenvinphos (Anon., 1988a). Samples are extracted with ethyl acetate in the presence of sodium sulfate. An aliquot of the extract is run on a TLC plate using an organic solvent mixture (chloroform/diethyl ether, benzene/acetone, benzene/acetone/hexane, or hexane/acetone). The plate is then sprayed with a homogenate of bee heads, incubated at 370°C and subsequently sprayed with a solution of 2-naphthyl acetate and Fast Blue B. The cholinesterase from the bee heads hydrolyses 2-naphthyl acetate to 2-naphthol, which reacts with the Fast Blue B to form a dye. Where inactivators of cholinesterase are present no dye is formed, so such places appear as white spots on a pink-violet background.
It was reported that 0.2 mg/kg of the (E)- isomer and 2 to <20 mg/kg of the (Z)- isomer could be detected. The method is not suitable for quantitative determination.
Fruit and vegetables, animal products, and grains. A quantitative multi-residue method, also submitted by The Netherlands, allowed determination of the (E)- and (Z)- isomers of chlorfenvinphos (Anon., 1988b,c). Samples are extracted with ethyl acetate in the presence of sodium sulfate, cleaned up where necessary by gel permeation chromatography using cyclohexane/ethyl acetate as eluant, and determined in the filtered extract by GLC with a phosphorus-specific detector. The LOD was stated to be in the range 0.01-0.05 mg/kg with a recovery of >80%, although no further information on validation of the method was given.
Carrots and onions. The Netherlands provided brief details of the methods of analysis used in the trials which they reported (Olthof, 1996). Extraction with petroleum ether or ethyl acetate is followed by analysis by GLC with FP detection. The limits of determination ranged from 0.005 to 0.02 mg/kg.
Crops and soil. In a method developed by Shell (Anon., 1966) samples were extracted by maceration with acetone in petroleum spirit in the presence of anhydrous sodium sulfate. After filtering, determination was by GLC with EC detection. Interfering co-extractives were removed with a Florisil column clean-up. An LOD of 0.01 mg/kg was reported although no chromatograms or details of the commodities with which this had been achieved were submitted. No recovery or other validation data were provided.
In a second reported method (Anon., 1990) soil was mixed with anhydrous sodium sulfate before extraction of soil and crop samples with acetone/hexane, and extracts of oily crops were partitioned between hexane and aqueous acetonitrile. The extracts were cleaned up on Florisil before analysis by GLC with an NPD. The method was validated with three soils (clay loam, sandy loam and silty clay), apples, soya beans, wheat grain and cabbage by fortifying with 0.05-0.5 mg/kg of each isomer. Recoveries were consistently between 75 and 115%. At each level the standard deviation was <12% of the mean. Sample chromatograms showed resolution of the isomers. The limit of determination was 0.01 mg/kg of each isomer in all samples.
A further method (Anon., 1969) was submitted for the determination of 2,4-dichloroacetophenone, 1-(2,4-dichlorophenyl)ethanol, and 2,4-dichlorophenacyl chloride. Crop and soil samples were extracted with a mixture of acetone and petroleum spirit. The extracts were washed with water, dried, and analysed by GLC with an ECD. Where required, an alumina column clean-up (elution with diethyl ether in petroleum spirit) was included. The method was stated to be suitable for determining metabolites down to a level of 0.01 mg/kg except 2,4-dichloroacetophenone, 2,4-dichlorophenacyl chloride and 1-(2,4-dichlorophenyl)ethanol. The LOD for the dichlorophenylethanol was 0.1 mg/kg.
Analysis of crops in supervised trials. Several other methods (Mathews, 1972; Bosio, 1981i) included in the reports of residue trials were modifications of the methods for crops reviewed above. Extraction was into either acetone/hexane or acetone/petroleum spirit and determination was by GLC with either FP or EC detection. LODs in the range 0.01-0.05 mg/kg were reported although generally no sample chromatograms were submitted. Some samples were analysed for 1-(2,4-dichlorophenyl)ethanol, 2,4-dichlorophenacyl chloride and 2,4-dichoroacetophenone, but with limited data on validation of the methods and few sample chromatograms. Confirmation of residues, when carried out, was by GC-MS.
Grass. Samples were extracted by tumbling with anhydrous sodium sulfate, acetone and petroleum spirit. The extracts were filtered and analysed without clean-up by GLC with an ECD (Elgar, 1966e).
Milk. In a briefly summarized method (Elgar, 1966e), samples of milk were diluted with ethanol and extracted with an ether/hexane mixture. After drying over anhydrous sodium sulfate the solvent was evaporated and the fatty residue washed with hexane and extracted into acetonitrile. The acetonitrile extract was cleaned up on Florisil columns, eluting with ether in petroleum spirit. Analysis was by GLC with EC detection.
Stability of pesticide residues in stored analytical samples
No data were submitted.
Residue definition
The studies of animal and plant metabolism indicate that chlorfenvinphos is the main residue in products of animal and plant origin. A definition of the residue as "chlorfenvinphos, sum of (E)- and (Z)- isomers" is therefore considered appropriate.
