Anticoincidence INAA capabilities for analysis of FDA Total Diet Study seafoods

Abstract

Anticoincidence instrumental neutron activation analysis was used to analyze three portions each of five fresh-weight FDA Total Diet Study seafoods from 3 Market Basket collections for fiscal years 2006–2008. Portions were treated with l-cysteine solutions to enhance retention of Hg during irradiation then dried at room temperature over magnesium perchlorate. Results or limits of detection were obtained for 33 elements. In general, results agreed with those available from FDA’s Kansas city field laboratory (KAN-DO). Of three shrimp composites analyzed, one showed mass fractions of Ag, Fe, rare earths, U, Th, and Mo significantly higher (up to a factor of 10) than the other two shrimp composites. The same shrimp composite showed a lower Hg result (about 50 % after accounting for any irradiation loss) compared to the KAN-DO value. This may represent a drying loss. There were other indications of Hg loss during the drying process. SRM 1947 Lake Michigan Fish Tissue, run as a control, yielded an INAA Hg mass fraction 20 % lower (corrected for irradiation losses) than the certified value, similar to the difference between the INAA (0.171 mg/kg Hg) and KAN-DO (0.211 mg/kg Hg) results for a TDS canned tuna composite. Because previous studies showed that l-cysteine effectively sequesters inorganic Hg, these discrepancies likely represent methyl mercury loss. INAA results for As, Fe, Rb, and Se were in good agreement with SRM 1947 certified values.