In this study, a new kinetic spectrophotometric method was developed to determine manganese using Indigo carmine (Ind) as a color reagent. This method is simple, rapid, sensitive and selective for the determination of trace amount of manganese ion in water. The oxidation reaction of Ind by H2O2 catalyzed by complex of Mn2+ with acrylamide (Acry) was monitored spectrophotometrically by measuring the decrease in absorbance of the system H2O-Mn2+-Acry-Ind-H2O2 (I). The fixed time (15s) and λmax (612 nm) were used. The limit of detection was 1×10-9 M. The relative standard deviation was 11.14% (n=7), relative error was 2.27 %, and the recovery was satisfactory (102.72%) for the determination of 0.022 mg/L. Three linear calibration curves, corresponding to concentration ranges of 10-9-10-8; 10-8-10-7; and 10-7-10-6 M, were obtained with linear regression coefficient R2>0.99. The method was applied to determination of manganese in drinking water in Hanoi, these results were compatible with atomic absorption spectrometry (AAS).
