Determination of trace vanadium in water samples with dispersive liquid-liquid microextraction (DLLME)-digital colorimetry (DC) was investigated. In an acidic medium, the interaction of vanadium with N-benzoyl-N-phenylhydroxylamine resulted in purplish red chelate complexes. In the DLLME, ethanol and chloroform were selected as dispersive solvent and extractant. Extract liquid was spotted into the silica gel TLC plate and then directly imaged by a digital camera. The spot gray scale integral value was proportional to the concentration of V(V). Thus a novel assay of trace vanadium based on DLLME-DC has been developed. Some important parameters that influence the extraction efficiency and the digital imaging result were studied and optimized. A good linear relationship was obtained in the range of 5.0～400 μg•L－1 of the V(V) (r＝0.9993) with the detection limit of 0.87 μg•L－1. This method has been applied for the determination of vanadium in environmental water samples with satisfactory results. The recoveries fell in the range from 97.4% to 102.7% and the relative standard deviations were between 1.7% and 3.3%. The method was proven to be low cost, simple, rapid, highly sensitive and environmentally friendly, which can meet the requirements for field detection.

Key words: dispersive liquid-liquid microextraction, digital colorimetry, vanadium, N-benzoyl-N-phenylhydroxylamine (BPHA), separation and enrichment, water sample