Determination of trace quantities of selenium and arsenic in canned tuna fish by using electroanalytical techniques

Abstract

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 HNO 3 and Mg(NO 3) 2, 6H 2O 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.