Determination of gold and indium in sea water by neutron activation analysis

Abstract

A combination of electrodeposition on graphite with neutron activation analysis was used for the determination of gold and indium in sea water. At a potential of -0.70 V vs. the silver-silver chloride electrode, gold and indium were electrolyzed on to a graphite electrode (1.1cmφ × 0.2cm) from 100ml of 0.5M sodium chloride. Recovery yield of gold was constant at pH from 1 to 3 and was independent of the initial concentration of gold, (0.011) ppb. For a 72-h electrolysis at pH 2 the recovery yield of gold was 92%, while that of indium was 32%. The graphite electrode was exposed to a thermal neutron flux of 5.1×10¹¹ or 1.5×10¹²n cm^-2 s^-1: 5min exposure for indium and 6 to 12 h for gold. After appropriate decay periods the activities of ¹⁹⁸Au and ^116mIn were measured for 2000s and 300s, respectively, with a 4000-channel pulse-height analyser and a Ge (Li) detector. The total amount of gold in 1 l of a sea water sample (Tokyo Bay) was (0.023 ± 0.001) μg, in which nonelectrolyzable gold was estimated to be 0.005μg. Indium concentration in the sample was too low to be determined by the present method. Detection limit for indium was 1 ppb.