Rapid Colorimetric Detection of Nickel in Metallic Clothing Accessories and Imitative Ornaments

The color reaction between Ni(Ⅳ) and dimethyglyaxime in an ammoniacal medium and in the presence of an oxidant to give a water soluble complex was applied to the rapid colorimetric detection of nickel in metallic clothing accessories and imitative ornaments. Sample with small size was shaked with 0.5 mL of 0.6 mol·L-1 HCl solution in a test tube for 30 s; for sample with large size, same amount of the HCl solution was added dropwise directly onto the surface of sample and rinsed for 30 s. An aliquot of 0.15 mL of the HCl extract was taken and placed in a micro test tube, and it was reacted with 1 drop each of 40 g·L-1 (NH4)3S2O8 solution and 300 g·L-1 sodium tartrate solution, and 3 drops of 10 g·L-1 ammoniacal solution of dimethylglyaxime. A reddish orange coloration was observed if Ni ion was present in the extract; and if Ni ion was not present, or more strictly the content of Ni was lower than 0.2 μg·cm-2, no significant color change was observed, and the sample was proved as up to standard.