Abstract:

A dispersive liquid-liquid microextraction (DLLME) method based on molecular complexation was developed for the determination of 2,5-dichloro-6-methoxybenzoic acid (dicamba) and 2,4-dichlorophenoxyacetic acid (2,4-D) in environmental water samples by high performance liquid chromatography-ultraviolet detection (HPLC-UV). Tri-n-butylphosphate (TBP) and methanol were selected as the extraction solvent and dispersive solvent, respectively. Parameters affecting the extraction efficiency, including the type and volume of the extraction and dispersive solvents, pH of the sample solutions, pH of the backward extraction solution, and salt addition, were optimized. Under the optimized conditions, the linear range was 0.50-1000 μg/L for the two target herbicides. The limits of detection (LODs, S/N=3) were 0.44 μg/L and 0.49 μg/L for dicamba and 2,4-D, respectively. The enrichment factors (EFs) of dicamba and 2,4-D were 85 and 90, respectively. The recoveries were in the range 75.7%-104.0%. The proposed microextraction involved molecular complexation, and the Lewis acid-base interactions between TBP and the acidic herbicides gave satisfactory extraction results. Thus, the method is expected to be a powerful tool for the determination of acidic herbicides in environmental water samples

Key words: dispersive liquid-liquid microextraction (DLLME), environmental water sample, high performance liquid chromatography (HPLC), phenoxy carboxylic acid herbicides, tri-n-butylphosphate(TBP)