Abstract:

An improved method was proposed to rectify false positive (FP) results from the determination of
organophosphorus and carbamate pesticides in garlic by enzyme inhibition method. Sample solutions were adjusted to the
optimum pH prior to detection, considerably reducing the inhibition effect of formed sulfides on acetylcholinesterase (AChE)
while allowing the determination of organophosphorus and carbamate pesticides. The results obtained for the determination
of blank garlic and pesticide solutions under different pH conditions indicated that pH adjustment in the optimum range of
about pH 8.0 to 9.0 of sample solutions was very effective for avoiding FP results without affecting qualitative identification
of organophosphorus and carbamate pesticides. For garlic samples spiked with varying conditions of 8 pesticides
(methamidophos, trichlorphon dimethoate, carbofuran, phoxim, chlorpyrifos, dichlorvos and carbary), the results obtained
at pH 9.0 showed a 91.7% consistency with those observed at pH 7.5. In conclusion, the improved pretreatment method
presented by adjusting pH in this study is simple, low-cost and effective and applicable for in situ rapid detection and can
also be expanded to other sulfur-containing vegetables.

Key words: enzyme inhibition method, peptide residue, garlic, sulfur-containing vegetables