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 predigestion 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 μg g−1, with an average concentration of 0·68 ± 0·27 μg g−1. The arsenic concentrations of the two cans analyzed were 1·62 μg g−1 and 2·41 μg 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 μg g−1 does, however, approach the maximum allowable level set by the FDA at 2·6 ppm.