Spectrophotometric determination of trace nickel(II) in fine coal ash with cloud point extraction

A new method utilizing non-ionic surfactant Triton X-114,which can be separated into two phases by heating to its cloud point,was developed to extract trace nickel(Ⅱ) in fine coal ash.A new method for the determination of trace nickel(Ⅱ) by double-wavelength spectrophotometry was developed using 475 nm and 540 nm as the detection wavelength.In the Na2B4O7-NaOH buffer solution of pH 9.5,nickel(Ⅱ) reacts with 1-(4-Nitrophenyl)-3-(5,6-Dimethyl-1,2,4-Triazol)-Triazene(NPDMTT) to form a stable complex.As a result,there were a positive absorption peak at 475 nm and a negative absorption peak at 540 nm.The results showed that Beer's law was obeyed in range of 0~120 μg/L for nickel(Ⅱ),and its apparent molar absorptivity was 7.29×105 L·mol-1·cm-1.When this method was applied to the determination of trace nickel(Ⅱ) in fine coal ash,its results were in good agreement with those provided by catalytic spectrophotometric method.The relative standard deviation was less than 5% and the recoveries of samples were between 98.0% and 102.7%.