OPTIMIZATION OF ANALYSIS OF METHYL-BROMIDE ON CHARCOAL SAMPLING TUBES

Analytical methods with low detection limits and large sample throughput are needed for environmental monitoring of methyl bromide emission into the atmosphere after fumigation. The effectiveness of the traditional solvent-phase analysis with carbon disulfide was compared with headspace analysis using a headspace autosampler on coconut-based ORBO-32 and petroleum-based ORBO-33 charcoal sampling tubes. Conditions for headspace analysis were optimized on the basis of the partition behavior of methyl bromide among the vapor, solvent, and solid phases in the closed system. Under optimum conditions, the detection limit using headspace analysis was 0.4 ng/tube, which was significantly lower than that for the solvent-phase analysis method (32 ng/tube). If 24 L of air is sampled, the equivalent detection limit in air concentration would be 17 ng/m(3) for the headspace method and 1300 ng/m(3) for the solvent-phase method. The headspace method is highly automated, and the number of samples that can be analyzed in 24 h is 300 under the proposed conditions, which is a significant improvement over all of the previously reported methods.