Development of a chronopotentiometric stripping method for the determination of selenium in mixed diets

Selenium is an element both toxic and essential for humans, animals and microorganisms. The selenium effect depends mostly on its chemical form and concentration. For the determination and monitoring of selenium content in different foodstuffs reliable and selective analytical method should be applied. In this work two modifications of the chronopotentiometric stripping analysis (CSA) using mercury film electrode were investigated and optimised. The first one included deaeration step (CSA-DEA) prior selenium deposition in the electrode, while applying medium-exchange technique (ME-CSA) time consuming deaeration step was avoided. Experimental parameters such as electrolysis potential, electrolysis time, dissolution current, linearity and the concentration of the CaCl2 were optimised in standard solutions of tetravalent selenium. Detection limits obtained for the CSA-DEA and ME-CSA modifications were 0.40 and 1.15 ppb, respectively. Interferences from copper, lead and iron were examined as well. For the methods verification standard reference material, wheat durum flour (RM 8436), was used. Two modifications of the chronopotentiometric stripping technique were applied for selective determination of total, Se6+, and the sum of Se0, Se2− and Se4+ in different samples of flour, garlic and sunflower seed. Recovery test as well as the analysis of the reference material confirmed the correctness of the defined methods. Selenium contents determined with two different modifications were in agreement.