Speciation of inorganic vanadium by direct immersion dual-drop microextraction coupled with graphite furnace atomic absorption spectrometry detection

In this work, a new method based on direct immersion dual-drop microextraction (DIDDME) was proposed for simultaneous speciation and enrichment of V(IV) and V(V) by graphite furnace atomic absorption spectrometry. This strategy was initiated with the chelation of V(IV) and V(V) in sample solutions with 1-(2-Pyridylazo)-2-naphthol (PAN). In the following step, two organic solvent drops hold on needle tips of microsyringes were concurrently immersed in the stirred sample solution to selectively and simultaneously separate V(IV)-PAN and V (V)-PAN complexes under the same pH value. This procedure avoided the tedious and complicated pre-oxidation/pre-reduction and centrifugation/filtration operations, which may cause the risk of sample contami-nation and analysis errors. Main parameters affecting the separation, preconcentration of the target species were investigated. Under the optimized conditions, the detection limits of this method were 2.4 ng/L and 1.5 ng/L for V(IV) and V(V) with relative standard deviations of 6.1 and 5.3 %, respectively. An enrichment factor of 300-fold was achieved for V(IV) and V(V). This method was applied successfully for the determination of V(IV) and V(V) in water samples. In order to validate the proposed procedure, a certified reference material of water sample was analyzed, and the determined value was in good agreement with the certified value.