Simultaneous determination of trace amounts of vanadium and cobalt in steel and environmental materials with 2-(5-nitro-2-pyridylazo)-5 [N-n-propyl-N-(3-sulfopropyl)amino]phenol by reversed-phase high-performance liquid chromatography

2-(5-Nitro-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]-phenol (Nitro-PAPS) is used as a precolumn chelating reagent for the reversed-phase high-performance liquid chromatographic separation and simultaneous determination of vanadium and cobalt. The metal-Nitro-PAPS chelates are separated on an ODS column with acetonitrile-water (55:45) containing 0.01 mol dm-3 acetic acid, 0.01 mol dm-3 tetrabutylammonium bromide (TBA+Br), and 10-4 mol dm-3 EDTA as an eluent. In this method, the vanadium and cobalt can be determined selectively at the sub-parts-per-billion level without any preliminary concentration and separation. The detection limits, defined as the concentrations equivalent to 3 times the standard deviation of the blank signal, are 17 ppt for vanadium and 55 ppt for cobalt at 0.002 absorbance unit full scale (593 nm). These results suggest that vanadium and cobalt in steel and environmental materials can be successfully determined without preseparation and preconcentration of these metal ions.