DETERMINATION OF TRACE QUANTITIES OF SELENIUM AND ARSENIC IN CANNED TUNA FISH BY USING ELECTROANALYTICAL TECHNIQUES

Fifteen brands and types of tuna fish were analyzed for selenium by using differential-pulse cathodic-stripping voltammetry. The cans with high and low concentrations of selenium were analyzed for arsenic by using differential-pulse polarography. Three samples with different levels of added As and a blank were analyzed for each can of tuna fish. Four sample-digestion methods with several variations of each were tested to determine the most reliable technique. An acid-digestion procedure using HNO3 and Mg(NO3)2, 6H2O with an 18-h pre-digestion step gave the best results, with an average recovery of 98.2%. The selenium concentration of the cans analyzed ranged from 0.034 to 1.20 mug g-1, with an average concentration of 0.68 +/- 0.27 mug g-1. The arsenic concentrations of the two cans analyzed were 1.62 mug g-1 and 2.41 mug g-1 in the low- and high-selenium cans, respectively. The selenium concentrations found in the tuna fish are not excessively high and do not seem to pose a problem. The arsenic concentration of 2.41 mug g-1 does, however, approach the maximum allowable level set by the FDA at 2.6 ppm.