Quantitative analysis of manganese, chromium and molybdenum by ion-pair reversed-phase high-performance liquid...

An ion-pair reversed-phase high-performance liquid chromatographic method with UV-visible spectrophotometric detection is proposed for the simultaneous determination of manganese, chromium and molybdenum. By using a C18-bonded silica column, 4-(2-pyridylazo)resorcinol (PAR) chelates of Mn(II), Cr(VI) and Mo(VI) were successfully separated and accurately determined at 480 nm. Tetrabutylammonium bromide (TBAB) was used as the ion-pair reagent. Effects of pH, the buffer system, the concentration of buffer, the color developing time, the concentration of chelating reagent and the ion-pair reagent on the resolution were investigated. PAR chelates were eluted within 20 min at a flow-rate of 1.0 ml min(-1) with a methanol aqueous mobile phase, CH3OH-water (20:80, v/v), containing 1.0 x 10(-3) mol l(-1) acetate buffer (pH 6.5), 1.8 x 10(-2) mol l(-1) TBAB and 2.0 x 10(-4) mol l(-1) PAR. The feasibility of the proposed method was verified with the standard reference materials of nickel-based alloys. The nickel-based alloys were analyzed chromatographically after ammonium pretreatment. Under the optimum conditions, the detection limits for the chelates of Mn(II), Cr(VI) and Mo(VI) were 0.31, 4.2 and 4.6 ng with 100 microl injection, respectively. The accuracy of the proposed chromatographic method was verified by good agreement between the values obtained by this method and certified values.