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2992950 
Technical Report 
Microanalysis of methyl bromide residues.) 
Asaka, S; Seguchi, K 
1973 
PESTAB/74/0244 
J 
J. Pestic. Sci. 
Japanese 
PESTAB Although methyl bromide residues in crops have been determined by GLC, it is difficult to concentrate the residue because of its high volatility. An attempt was made to obtain derivatives offering specificity and selectivity in GLC, and it was found that O,O-diethyl S-methyl dithiophosphate (DEMDP) and 2,5-dichlorophenyl methylsulfide (DCPMS) serve for the purpose. The derivatives were synthesized by bubbling methyl bromide, stripped from the specimens by codistillation with a nitrogen stream, into a methanolic solution of either ammonium O,O-diethyl dithiophosphate or 2,5-dichlorobenzenethiol, with yield of 99-109%. The excess regent, which interferes with the determination, was removed by liquid-liquid extraction. As little as 0. 5 ng of DEMDP and DCPMS could be detected by FID and ECD. With FTD, the high selectivity of the detector made the determination easier, and the reaction mixture could be condensed to increase the detection sensitivity. The recovery of methyl bromide from wheat grain and poultry feed fortified at 0. 5 ppm was 80. 4 and 81. 1% after conversion into DEMDP. Recovery from wheat grain and poultry feed fortified at 10 ppm was 82. 0 and 81. 0% after conversion to DCPMS, respectively. The sensitivity was 1 ppb, adequate for residue analysis.