DETERMINATION OF TRACE SILICON IN HIGH-PURITY NICKEL USING A MASKING REAGENT FOR THE MATRIX ELEMENT

To determine trace silicon in high purity nickel samples a modified fluoride separation-molybdosilicic acid blue spectrophotometric method using a masking reagent for nickel was developed. The analytical procedure is as follows; dissolve 1.0 g of the sample in 6 ml of nitric acid by heating and replace the acid with 6 ml of perchloric acid by fuming. After cooling the solution, add citric acid 5 g as masking reagent and hydrofluoric acid (0.5%) 0.5 ml and then sulfuric acid 20 ml, to yield volatile silicon tetrafluoride. Transport the fluoride completely into a boric acid solution by purging it with nitrogen. Then, transfer the solution into a 25 ml flask, and add hydrorchloric acid and ammonium molybdate to form molybdosilicate. After adding oxalic acid and ascorbic acid, measure the absorbance of the solution at 810 nm. By this method, ppm level silicon in commercial high purity nickel samples (3N, 4N and 5N) was successfully determined. Recovery (n = 10) was 97% for 10 mug of silicon and the detection limit (corresponding to 3sigma of blank value) was 0.09 mug in 1 g of sample.