Simultaneous determination of vanadium(IV) and vanadium(V) by flow injection analysis using kinetic spectrophotometry with Xylenol Orange

A flow injection method of analysis has been developed for the simultaneous determination of V(IV) and V(V) using the difference in the rate of complex formation between vanadium in two different oxidation states and Xylenol Orange in acidic media. The proposed method used a spectrophotometric detector equipped with two flow cells aligned with the same optical path to yield two successive peaks per each sample injection. V(IV) and V(V) were determined by solving simultaneous equations in two unknowns, the concentrations of V(IV) and V(V), obtained from measurements of the two peak heights. The detection limit calculated as 3σ of noise signals was 0.01 μg/mL for both V(IV) and V(V). The relative standard deviations for V(IV) and V(V) at the 1 μg/mL level were 1.6 and 2.4%, respectively. The sample throughput was found to be about 19 h−1. The proposed method was successfully applied to the simultaneous determination of V(IV) and V(V) in synthetic scrubbing solutions used in desulphurization with reasonable accuracy.