Determination of Vanadium(IV) and Vanadium(V) in Beverages by Two-Step Direct Immersion Single-Drop Microextraction with Graphite Furnace Atomic Absorption Spectrometry (GFAAS)

A novel two-step direct immersion single-drop microextraction (TS-DI-SDME) was reported for the sequential separation and enrichment of V(V) and V(IV) followed by graphite furnace atomic absorption spectrometry detection. Theonyltrifluoroacetone (HTTA) and chloroform were used as the chelating reagent and extraction solvent for TS-DI-SDME. In the first step, V(V)-HTTA complexes were separated and enriched in one organic solvent drop at pH 2.5, while V(IV) remained in the solution. Next, another organic solvent drop containing HTTA was immersed in the original solution after the extraction of V(V) for the enrichment of V(IV) at pH 4.5. This procedure avoids tedious and complicated pre-oxidation/pre-reduction operations, which may cause contamination and error. Under the optimized conditions, the limits of detection were equal to 3.1 and 2.6 ng L-1 for V(IV) and V(V) with relative standard deviation values of 4.9 and 5.8%, respectively. An enrichment factor of 300-fold was achieved for V(IV) and V(V). This method was successfully utilized for the determination of V(IV) and V(V) in beverages. To validate this approach, a water-certified reference material was analyzed with satisfactory results.