Radiochemical neutron activation analysis of total trace tin and determination of its differentiated compounds in aquatic biota

Summary

The optimization of extraction and determination of trace tin using radiochemical neutron activation analysis (RNAA) in selected aquatic specimen (algae, fish, mussels) is described. Neutron activation analysis (NAA) using the induced ^117mSn (13.6 days) or ¹¹³Sn (115 day) nuclides is in principle a sensitive method for determination of total trace tin. However, due to the high contents of arsenic (As) in most marine matrices, neutron irradiation induces high levels of ⁷⁶As (26.3 h) in comparison to weak ^117mSn activities. Selective removal of As by absorption on Acidic Aluminum Oxide (AAO) would be advantageous and reduce the activities required to be handled during tin purification. It was found that perchloric acid medium is the best eluent for separating Sn from As, whereas sulfuric acid and a mixture of the two were not as effective. The standard radiochemical separation procedure based on solvent extraction and purification of tin iodide in toluene from sulfuric acid-potassium iodide (KI) medium with recoveries ranging between 90%–95% is applied. Interferences from the ⁴⁷Ca/⁴⁷Sc decay and ¹⁹⁹Au with similar gamma energies were effectively removed by the liquid/liquid separation. Comparing the total tin content in freeze-dried samples with the total organotin content in fresh samples shows that the drying process has changed the tin species pattern of the material. The total butyltin content represents 60% and 90% of the total tin content in eel-pout and bream muscles, while it represents about 76%–83% and 58%–88% in mussels and algae, respectively.