Abstract
A method has been developed for the determination of traces of gold in pure copper by neutron activation analysis using ion exchange preconcentration.
The sample was dissolved in a mixture of HNO3 and HCI, and the solution (1 g of copper in 35 ml) was passed through a small column packed with 150 mg (wet basis) of Dowex AG 1 X 8 anion exchange resin (Cl-form; 100 200 mesh) to separate gold from copper. After being washed with deionized water, the resin was treated with 10 ml of 0.1 N NH4SCN solution to be converted into SCN-form, and finally with water.The resin was transferred into a polyethylene bag and dried in an electric oven at 75°C for 10---15 hr, and then heat-sealed off.
The resin samples together with standards were irradiated with pneumatic tube system of JRR-2 reactor at a flux of 7 x10" n/cm2/sec for 20 min. After cooling for 2-s4 days their ractivities were counted with a Ge(Li) or a NaI(Tl) detector without futher chemical treatment.
The interference elements in Cl- and SCN-form resins were preliminarily determined and found to be mainly Cl, Br, Na, Mn and Hg. In the radioactive nuclides formed by (n, r) reaction, "Br gave the strongest interference in the counting of 0.412 MeV T-ray from '"Au, because 82Br is of a similar half-life with '"Au and emits r-rays of energies higher than 0.412 MeV. By converting Cl-form resin to SCN-form, the amount of Cl as well as Br was so much decreasable that the S/N ratio of 0.412 MeV photopeak could be much improved. Interference by radioactive Cl, Mn and Na was negligible after cooling for 2 days. Hg scarecely interfered with the present measurement, because of its lower T-ray energies than that of "BAu. The amount of copper remaining in resin after previous chemical separation was about 5.2 pg per 200 mg resin (wet basis). Its interference could be reduced to be negligible by cooling it for 3---4 days.
At present, the chemical yield and concentration factor of gold were about 97% and 1.9 x 105, respectively. Analytical results of gold in 99.99% Cu were 0.06-0.07 ppm, and blanks were< 0.001 ppm. Theoretical limits for qUantitative determination and quantitative detection were estimated to be 0.0O2- ppm and 0.0006 ppm, respectively.
