Abstract：The conditions for color reaction of 4-(2-pyridineazo)-resorcinol (PAR) with niobium was investigated, and a method for the determination of niobium in acid sludge (which was expressed as niobium pentoxide) by spectrophotometry was developed. The results showed that in the solution at pH 5.6-6.0, a red ternary complex was formed by PAR with the complex anion of niobium tartrate in the presence of beryllium salt and tartaric acid, and its maximum absorption wavelength was 550 nm with apparent molar absorptivity (ε) of 2.6×104 L·mol-1·cm-1. Under the optimum experimental conditions, there was a good linear relationship between the niobium pentoxide concentration within the range of 0.02 to 0.8 μg/mL and its corresponding absorbance, the correlation coefficient (r) was 0.998 8 and the detection limit was 0.004 8 μg/mL. The method was used for the determination of niobium in acid sludge. The results were in accordance with those obtained by chlorosulphophenol S spectrophotometry, and the relative standard deviations were 2.1%-2.5%.
