The determination of vanadium(V) in the presence of vanadium(IV) using 4-(2-pyridylazo)resorcinol in a flow-injection manifold

A method was developed for the determination of V(V) in the presence of V(IV) using flow-injection analysis (FIA). In this method, V(V) forms a coloured complex with 4-(2-pyridylazo)resorcinol (PAR), while a complexing agent, 1,2 cyclohexanediaminetetraacetic acid (CDTA) was added to mask the interference from V(IV) in the sample. The absorbance of the V(V)-PAR complex was measured using a laboratory-built flow-cell containing a light-emitting diode (LED) and a photodiode. The effect of variables such as the pH, reaction time and CDTA concentration on the V(V) peak height was examined. After the manifold had been fully optimized, the system was incorporated into a process analyser, in combination with a gradient dilution step. This allowed V(V) to be determined in the range 0.05–1.5 g/1. The relative standard deviation (sr) at the 0.1 g/1 V(V) level (n=10) was 0.03.