A multi-residue method for the determination of organochlorine, organophosphorus and synthetic pyrethroid pesticides and carbaryl in grain is presented. After extraction with acetone -methanol, the pesticides are separated from co-extractives by a partition process with dichloromethane and chromatography on an acidic aluminium oxide column. Quantitative determinations are made by packed column gasliquid chromatography using an electron-capture detector for the organochlorine pesticides and a flame-photometric detector for the organophosphorus pesticides. High-performance liquid chromatography using an ultraviolet spectrophotometric detector is used for the determination of synthetic pyrethroids and carbaryl. Capillary column gas -liquid chromatography is used for confirmation of identity of suspected residues of organochlorine, organophosphorus and synthetic pyrethroid pesticides.
A multi-residue method for the determination of synthetic pyrethroids in fruit and vegetables is .presented. After extraction with hexaneacetone, the pyrethroids are separated from co-extractives by a partition process and chromatography on a silica gel column and quantitatively determined by electron-capture gasliquid chromatography and/or high-performance liquid chromatography using an ultraviolet spectrophotometric detector. Keywords : Synthetic pyrethroids ; gasliquid chromatography ; high-performance liquid chromatography ; f r u i t and vegetables ; residues Crown Copyright.
A review is presented of the analytical methods for the detection and determination of polychlorodibenzo-p-dioxins and polychlorodibenzofurans in phenoxyalkanoic acid herbicides.
A method for the determination of dithianon in apples is presented. After extraction with acetonehydrochloric acid, the dithianon is separated from co-extracted compounds by a partition process and chromatography on a silica-gel column before quantitative determination by high-performance liquid chromatography using an ultraviolet spectrophotometric detector. Confirmation of residues may be achieved by high-performance liquid chromatography using post-column derivatisation.
Pyrimethamine [5-~-chlorophenyl-6-ethylpyrimidine-2,4-diamine] is used in rabbit and poultry feeds at levels of 5-7.5mg k g l for the prevention of coccidiosis. It is normally used in the presence of sulphaquinoxaline, with which it exerts a synergistic effect.A spectrophotometric method for the determination of pyrimethamine in animal feeds was described by Garber et a1.l This method is based on the formation of a complex betweeen pyrimethamine and bromocresol green in aqueous solution. In our experience, this method is subject to interference from certain ingredients in some feeds, particularly grassmeal. The method for the determination of pyrimethamine in feeds by HPLC recently described by Cox and Sugden2 allows determinations only to the nearest 1 mg kg-1.Methods for the determination of pyrimethamine in animal tissue have been described by Cala et aL3 (gasliquid chromatography), and Golinskii and Repin4 (adsorption chromatography). However, neither of these methods is directly applicable to animal feeds, Royere et al.5 described a gasliquid chromatographic method for the determination of pyrimethamine in animal feeds. The method involves the extraction of pyrimethamine with 50% hydrochloric acid followed by determination using an electron-capture detector. However, when the method was applied in this Laboratory to compound feeds it was not possible to resolve the pyrimethamine peak from those of co-extractives and difficulty was often experienced during the clean-up stages owing to the formation of emulsions. It was considered that the use of an organic solvent to reduce the amount of co-extracted material, coupled with a more thorough clean-up procedure, would permit satisfactory determinations by gas-liquid chromatography. In the Report of the Government Chemist for 19746 a modification to the method of Garber et a1.l was described in which the extraction solvent was changed from benzene to methanol; the latter solvent has been retained for the method described in this paper.
Experimental ApparatusA gasliquid chromatograph fitted with a nickel-63 electron-capture detector (Pye, Model GCV, fitted for on-column injections) was used, with a glass column (1 m x 4mm) containing 10% m/m Versamid 900 on Diatomite CLQ (80-100 mesh). The carrier gas was nitrogen (oxygen free) at a flow-rate of 50ml min-l and the purge gas was also nitrogen (oxygen free) at a flow-rate of 30 ml min-l. The column was maintained at 230 "C, the injector port at 250 "C and the detector at 300 "C.A sintered-glass micro-filter, porosity 1, i.d. 10 mm (available from Scientific Supplies Co. Ltd., London), and a rotary vacuum evaporator were used.
ReagentsSodium sulphate, anhydrous. Heated overnight at 350 "C.
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