Determination of selenium species in biota with an emphasis on animal tissues by HPLC-ICP-MS

Measuring Se species concentrations is important to understand its bioaccumulation, metabolic pathways and toxicology. This review examines the different extraction protocols used to isolate and measure Se species from biota, as well as, separation of the major Se species found in animal tissues by High Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry (HPLC-ICP-MS). Extraction protocols group into three classes based on reagents used: (i) aqueous solutions, (ii) enzymes, and (iii) acids and bases. The major Se moieties present in animal tissues are the selenoamino acids, selenomethionine (SeMet) and selenocysteine (SeCys). These can be released by enzymatic hydrolysis. SeMet in the enzymatic extract remains stable and can be separated by ion exchange or reverse phase chromatography. SeCys, however, is not stable as it decomposes into alanine and Se and must be stabilised prior to enzymatic extraction by derivatisation. This is commonly achieved by using urea to denature proteins and dithiothreitol to break the Se-Se and S-Se bonds with the SeH groups formed stabilised by alkylation with iodoacetamide to form CAM-SeCys. Size exclusion chromatography is then used to isolate and concentrate the derivatised selenoamino acid fraction and ion exchange or reverse phase chromatography used to separate derivatised Se species. When measuring Se concentrations by ICP-MS, carbon enhancement in the ICP plasma and isobaric inferences from chloride-, sulfur-, bromine and oxygen containing matrices need to be considered. The use of dynamic reaction cell or collision cell minimises or eliminates these interferences, but in practice few interferences coelute with Se species. (C) 2015 Elsevier B.V. All rights reserved.