An On-line Thiourea Pre-reduction Of Hexavalent Selenium-Hydride Generation Interface Between HPLC And AFS And Its Application To Selenium Speciation Analysis

Currently, hyphenated technique is the most frequently used in selenium (Se) speciation. Because the bioavailability and/or toxicity of Se are species dependent, Se speciation has become a subject of increasing interest in recent years. The main contributions of this thesis are developing a new on-line reduction system for SeO₄^2- (Se(VI)) by thiourea (TU) and, proposing the possible mechanism of reduction. Based on these fundamental researches, "an on-line dynamic controlled" pre-reduction of Se(VI) followed by KBH₄/NaOH-HCl hydride generation (HG) system was used as an interface between HPLC and AFS. There are three chapters in this thesis as follow.In Chapter One, the distribution of Se in nature and its biological functions were briefly introduced; a review of the recent advances of the selenium speciation analysis was presented, focusing on the techniques of separation, interface, element-specific detection and identification of selenium species.In Chapter Two, thiourea (TU) on-line pre-reduction of Se(VI) before reaction with KBH₄/NaOH-HCl was developed. The possible pre-reduction mechanism was also discussed. When TU-HG was used as an interface between ion-pair HPLC and AFS, four most common Se species such as selenocystine, selenomethionine, Se(IV) and Se(VI) could be simultaneously and quantitatively analyzed by IP-HPLC-(TU/HG)-AFS; Furthermore, IP-HPLC-(TU/HG)-AFS system was successfully applied to Se speciation in certified reference material NIST 1946 and cultured garlic samples. To our knowledge, this is the first report that TU is used as the pre-reductant for Se(VI) in Se speciation analysis.In Chapter Three, IP-HPLC coupled with ICP-MS equipped with DRC was established and applied to determination of the speciation of trace elements, especially Se, in the plasma and blood of outpatients living in Se-riched area, enshi, Hubei province, China. Results showed that selenocysteine concentration remains constant in a certain level while selenomethionine concentration increases linearly with the total Se concentration of the blood.