SELENIUM SPECIATION IN HUMAN-MILK WITH SPECIAL RESPECT TO QUALITY-CONTROL

Selenium- (SE) organo compounds of pooled human milk (7th-14th d after delivery) were separated by centrifugation and subsequent size-exclus ion chromatography (SEC) as described in ref. (1). The SEC fractions w ere used for Se determinations by electrothermal vaporization inductiv ely coupled plasma mass spectrometry (ETV-ICP-MS) in parallel to ident ification procedures of the organic ligands by two different capillary zone electrophoresis (CZE) methods. Further, the combination of isota chophoresis- (ITP) CZE with ETV-ICP-MS was used for final identificati ons. Mass balances were carried out at each analytical step for qualit y assurance. Reinjection experiments were performed to check the stabi lity of Se-organo compounds during the analytical procedure. These qua lity-control experiments showed that no species transformations took p lace during the analytical procedure, and the Se species were native i n human milk. The identification and quantification of organic ligands were clear and resulted in values of 2 (+/-0.2) mg/L GSH/GSeH, 2 (+/- 0.22) mg/L cystamine/Se-cystamine, 4 (+/-0.4) mg/L cystine/ Se-cystine , and 1 (+/-0.18) mg/L methionine/Se-methionine. Unfortunately, a diff erentiation between sulfur (S) and Se analogs was not possible with th e applied CE methods. The Se values per organic ligand were determined as 2.5 (+/-0.23) mg/L associated with GSH (as GSeH), 3.1 (+/-0.31) mg /L associated with cystamine (as Se-cystamine), 5.2 (+/-0.4) mg/L asso ciated with cystine (as Se-cystine), and 1 (+/-0.1) mg/L associated wi th methionine (as Se-methionine).