Method Development and Removal of Methyl Bromide Residue Determined as Total Inorganic Bromide in Rice by Gas Chromatographic Technique

Abstract

       Methyl bromide is mainly used as a fumigant for postharvest treatment of plant products. Especially, rice and grains are fumigated to eliminate undesired pests before commercializing. Inorganic bromide is resulted from repeating fumigation of methyl bromide and reacts chemically with some constituents of the material. This study was consequently conducted by using modified Stijve T. method to determine total inorganic bromide in rice. The comminuted ground samples are suspended in an acidified aqueous solution of propylene oxide, with bromide being simultaneously extracted and derivertized into 1-bromopropane-2-ol and 2-bromopropane-1-ol which can be detected by GC-μECD. As a result of method validation, limit of detection (LOD) and limit of quantitation (LOQ) are 2 and 5 mg/kg, respectively. The accuracy expressed as mean of %recovery by using external standard calibration at 5, 25 and 50 mg/kg were found to be 96.9, 93.4 and 94.3% respectively and those results obtained by using 3-bromopropane-1-ol as the internal standard were also found to be 94.5, 89.2 and 86.9% respectively. The method precision expressed as HORRAT were in the acceptable range which less than 2 in both cases. In addition, the linearity was found to be in the working range of 5-75 mg/kg with Pearson’s correlation coefficient (r) = 0.999. The result of the validation study demonstrated that, there was non-significant difference between the result obtained from external and internal standard calibrations at the LOQ (level of confidence=95%, ∝ =0.05). The performance characteristics of this method were fit for intended use according to maximum residue limit established by CODEX and Thai Ministry of Public Health set at 50 mg/kg.