A new method to determine the amount of methiocarb and its two metabolites,
the sulfoxide and sulfone in soil and rice plant is described. The method
consists of extraction of samples with acetone, filtration, separation of m
ethiocarb and its metabolites through a Florisil column, and gas chromatogr
aphic determination. Since the degradation of methiocarb to 3,5-dimethyl-4-
methylthiophenol (DMMP) is commonly observed during GC analysis, methiocarb
was converted to DMMP via chemical hydrolysis after column chromatography.
Reasonable recoveries for routine analysis were obtained and the limit of
quantitation (LOQ) with GC/FPD were 0.5, 2 and 2 ng for DMMP: sulfoxide and
sulfone, with a signal to noise ratio of 4. In all rife samples, no detect
able residues were found, however DMMP and methiocarb sulfoxide were found
in some straw samples. In field soil samples, no sulfone was detected in al
l samples and methiocarb showed typical degradation curves with a half life
of 8 days after treatment. A five-fold longer half life was observed in in
door studies.