GC-MS Determination of 2,4-D and Bentazone in Water with Pretreatment by SPE and Pre-column Derivatization

Two herbicidal chemicals,2,4-D (dichloro-phenoxy acetic acid) and bentazone in water samples were separated and enriched by SPE on Oasis HLB SPE micro-column. Mixed solvent of CH3OH and methyl-tert. butyl ether (10+90) was used to elute the 2 herbicidal chemicals from the column and the eluate was dried by N2-blowing,made up to 1.0 mL with hexane and used for GC-MS determination after pre-column derivatization with iodomethane-dichloromethane (10+90) solution and tetra-butyl-ammonium hydrogen sulfate-NaOH solution. Linear relationship between values of peak area and concentration of either 2,4-D or bentazone was obtained in the range of 0.1-5.0 mg·L-1. Values of lower limit of determination (10S/N) found were 0.02 μg·L-1 for 2,4-D and 0.10 μg·L-1 for bentazone when 200 mL of water samples were introduced.