Chiang Mai Journal of Science

Metal ion extraction combined with colorimetric method has been developed to determine Ni^II ions. Dimethylglyoxime (DMG) was added in a trace Ni^II solution served as extracted chelating agent for the Ni^II ions forming a reddish pink Ni^II-DMG particle. Determination at the parts per million level of Ni^II (0.5-5.0 ppm) was achieved by filtration of color Ni-complex on a filter paper, followed by simultaneous colorimetric analysis using a UV-VIS spectrophotometer (540 nm). Optimized pH of the Ni^II-DMG forming reaction giving uniform size and shape of Ni^II-DMG complex particles, was found to be at pH 9 buffered with sodium tetraborate. The detection limit (3-sigma) of the Ni^II determination by this method was 0.4 ppm. The accuracy and precision of the test method were evaluated on the recovery and relative standard deviation of the Ni^II determination (10 sets) at 1 and 2 ppm. Recovery percentages of the Ni^II detection at 1 and 2 ppm were 102 and 106%, while relative standard deviations were 5.8 and 4.6%, respectively. Interference ions were studied and found that AlIII and Cr^III strongly interfered with the Ni^II determination. This could be solved by an addition of 0.2 mM N, N-dihydroxyethylglycine as a masking reagent giving good results of the detection of NiII at 1 and 2 ppm. The present method was applied for the detection of real water samples including tap water, river water and treated textile wastewater spiked with 1 and 2 ppm of Ni^II. The test results were accurate and precise to determine wastewater prior to discharge into the environment. This detection system enables simple and reliable on-site monitoring of Ni^II.