Catalytic determination of cobalt(II) with arsenazo III in a strong alkaline medium

A catalytic analysis based on a decomposition reaction of ate compounds is a highly sensitive determination method of Co (II). In the system which makes an ate compound to be an indicator reagent, metal complex formation with the ate compound is necessary for metal ions to be a catalyst. The arsenate III used in this study as an indicator reagent is known to be a colorimetry reagent of rare earths. However, the formation of a complex with Co(II) was not known. It was found that Co(II) formed the complex in a strong alkaline medium and that it accelerated the color-fading reactions of arsenate III. Then, a catalytic analysis method of Co(II) by arsenazo III in a strong alkaline medium was examined. A calibration curve was made between ln(A(1)/A(10)) and the concentration of cobalt(II), where A(1) and A(10) were the absorbance of arsenazo III solution at 1 min and 10 min, respectively The values of 1n(A(1)/A(10)) were nearly proportional up to 20 ppb of cobalt (under the optimum conditions: pH 13.7, 1.9 x 10(-5) M arsenazo III, 1.0% H2O2 and 45 degreesC). The detection limit was 0.5 ppb This method was applied to the determination of cobalt in silica gel without requiring any complicated pretreatment.