2-(5-Nitro-2-Pyridylazo)-5-(N-Propyl-N-Sulfopropylamino)Phenol as a new analytical reagent for flow-injection spectrophotometric determination of trace vanadium(V)

Abstract

Abstract.A flow injection method using 2-(5-nitro-2-pyridylazo)-5-(N-propyl-N-sulfopropylamino)phenol-(Nitro-PAPS) as a new chromogenic reagent is presented for sensitive and rapid determination of vanadium. Nitro-PAPS reacts with vanadium(V) in weakly acidic medium to form a water soluble complex of molar absorptivity of 8.0 x 104L mo1-1 cm -~ at 592nm (maximum absorption wavelength), which permits the straightforward application of a flow injection system to the sensitive determination of vanadium. Under the optimum conditions established, a linear calibration graph was obtained in the range 1-120 ng mL -1 . The relative standard deviation for 60ngmL -I vanadium was 2.2% (n= 5) and the limit of detection was 1 ng mL -1. The sample throughput is about 40 h-1. Most inorganic and organic anions examined did not interfere even at concentrations of 3000-6000 times of vanadium. Interference from cobalt(II), copper(II) and nickel(II) at 200ngmL -1 levels can be overcome by the addition of N-(dithiocarboxy)sarcosine. The recoveries for each 20 and 10ngmL -t vanadium added to the river water were 98 and 97%, respectively.Key words: Nitro-PAPS, vanadium, spectrophotometry, FlA.It has been shown that heterocyclic azoderivatives provide highly sensitive chromogenic reagents for some heavy metals which form complexes having molar absorptivities approaching to 105L mol -I cm -1 [1-6]. 2-(5-Nitro-2-pyridylazo)-5-(N-propyl-N-sulfo-* To whom correspondence should be addressed propylamino)phenol(Nitro-PAPS) is a recently synthesized chromogenic reagent giving complexes of high molar absorptivity with metals and good water solubility of both the reagent and its metal complexes [7]. Water solubility of the reagent and its metal complex is one of the important requirements for its use in flow-injection analysis (FIA) which is a rapidly growing analytical technique. Despite of expectable high analytical potential, analytical studies using the Nitro-PAPS have been found only for zinc [8], copper [9] and iron [10,11] determinations to date. Recently we have studied the Nitro-PAPS applied to sensitive post-column reaction detection in ion chromatography of cadmium, lead, and manganese [12]. In addition, we have found that Nitro-PAPS forms a water soluble complex of molar absorptivity of 8.0• 104L mo1-1 cm -1 with vanadium in weak acidic media and thus has potential usefulness to be applied for spectrophotometric determination of vanadium in a FIA system. In the present work, potential analytical significance of such complex formation of Nitro-PAPS with vanadium was studied in detail and a FIA method based on its use is described for the determination of trace vanadium. It has been assumed that Nitro-PAPS ranks as one of the most sensitive chromogenic reagents known for V(V). Experimental Reagents and SolutionsUnless otherwise noted, all reagents were of analytical grade and were used as received. Nitro-PAPS stock solution (1.0x t0 3 M) was prepared by dissolving the reagent (Dojindo, Kumamoto) in