Use of NO^3-form Anion Exchange Resin for Neutron Activation Analysis of Gold in Zinc'

Abstract

A method has been developed for the determination of traces of gold in pure zinc by neutron activation analysis using ion exchange preconcentration.
Five grams of sample was transferred to a 50 ml beaker and dissolved in a least amount (about 30 ml) of 9: 1 mixture of HNO₃ and HCl. The sample solution was slowly cooled to room temparature, on standing, then diluted to 50 ml with water, and then passed through a small column packed with 150 mg (wet basis) of Dowex 1-X 8 AG anion exchange resin (Clform, 100-200 mesh) to separate gold from zinc (see Fig.1). Then, the resin was treated with 15 ml of 0.2 N HNO₃ solution to convert to NO^3-form, and finally washed with water. The resin was transferred into a polyethylene bag and dried in an electric oven at 75°C for about 10 hours, and heat-sealed off.
The resin samples together with standards were irradiated with pneumatic tube system of JRR-2 reactor at a flux of 7x 10" n/cm²/sec for 20 minutes. After being cooled for about 5 hours to allow 28Cl to decay out, the irradiated resin was slurried with water and transferred into a column previously packed with 50'-.400 mg of non-irradiated Dowex 1-X 8 resin (Cl-form, 100-200 mesh), then treated with 20 ml of 0.5 N HCl solution to elute out the interfering nuclides (see Table 1). 198Au remained on resin was then counted with a Ge (Li) detector after cooling for about 7 hours, or with a NaI (T1) detector after cooling for about 1 day.
The chemical yield of gold was about 98%, and the concentration factor was 2.2 X 107. The blank was 0.05 ng on an average. The minimum determinable and detectable masses are thus presumed to be about O.5 ng (10-fold of blank) and 0.1 ng (2-fold. of blank), respectively.