Challenges in the accurate speciation analysis of selenium in humans: first report on indicative levels of selenoproteins in a serum certified reference material for total selenium (BCR-637)

Se is one of the most investigated essential trace elements in the past years, mostly due to its cancer prevention properties. Nevertheless, the accurate determination of its biologically active species, such as the selenoproteins (SeProt) in human serum, is currently a challenging task. This is because of the lack of appropriate quantification standards, certified reference materials (CRMs), and/or reference measurement methods. Additionally, most of the methods developed so far for the determination of SeProt were applied to the analysis of control (volunteers) serums, which are not available to other laboratories, therefore making methods inter-comparison virtually impossible. We present here for the first time indicative levels of SeProt in a commercially available human serum, namely the BCR-637 CRM with certified level of total Se. The concentrations of selenium associated with glutathione peroxidase (GPx), selenoprotein P (SelP) and selenoalbumin (SeAlb) in this serum were calculated using the results obtained by 13 different analytical methods (literature and non-published data) on the basis of (affinity) high-performance liquid chromatography (AF-HPLC) coupled to inductively coupled plasma-mass spectrometry (ICP-MS). The indicative levels of SeProt in the BCR-637 serum can be used for validation of methods dealing with the determination of these proteins in human serum.     

Simultaneous speciation analysis of glutathione peroxidase,selenoprotein P and selenoalbumin in human serum by tandem anion exchange-affinity HPLC and on-line isotope dilution ICP-quadrupole MS

A method based on anion exchange (AE) and affinity (AF)-HPLC (AE-AF-HPLC) hyphenated to inductively coupled plasma-(quadrupole) mass spectrometry (ICP-QMS) was developed for the speciation analysis of selenoprotein P (SelP), glutathione peroxidase (GPx) and selenoalbumin (SeAlb) in human serum. AE-HPLC is proposed here for the on-line alleviation of Cl and Br spectral interferences on ⁷⁷Se (⁴⁰Ar³⁷Cl) and ⁸²Se (⁸¹Br¹H). Separation of GPx, SelP and SeAlb by AE-AF-HPLC was obtained within a total chromatographic runtime of <20 min. On-line (post-column) isotope dilution (ON-ID) and on-line external calibration (ON-EC)-ICP-QMS were used for the quantification of Se in GPx, SelP and SeAlb. ON-EC using a Se-L-cystine standard was shown to be a suitable approach for the routine simultaneous speciation analysis of serum GPx, SelP and SeAlb. The method validation was carried out by direct ICP-sector field MS determination of Se in GPx, SelP and SeAlb fractions collected after AE-AF-HPLC separation. In addition, the method accuracy for the determination of total protein-bound Se was assessed by analyzing a human serum reference material (BCR-637) certified for total Se content. Figure A methodology for the alleviation of Cl and Br interferences in the accurate simultaneous speciation analysis of glutathione peroxidase, selenoprotein P and selenoalbumin in human serum by affinity HPLC coupled on-line with ICP-quadrupole MS is proposed. This approach may be particularly useful for clinical laboratories that only have an ICP-quadrupole MS without a collision cell, or that lack an expensive ICP-SFMS (high-resolution) instrument     

A metrological approach for the assessment of selenium status in human serum

This work addresses a metrological approach for the assessment of Se status in humans in terms of serum selenomethionine (SeMet). The quantification of SeMet was carried out using a primary method of chemical analysis, namely species-specific isotope dilution (SSID) in combination with HPLC coupled to collision/reaction cell inductively coupled plasma-mass spectrometry. SeMet was released from the serum selenoalbumin (a seleno-containing protein where SeMet is randomly incorporated) by enzymatic hydrolysis of the whole serum. This study is a follow-up of the analytical method development reported previously, and it focuses primarily on the evaluation of the uncertainty budget and the main uncertainty sources for SeMet determination in three commercial serums, namely BCR-637 (certified for total Se) and two serum standards, SERONORM level 1 (SERO-L1) and 2 (SERO-L2) (with indicative concentrations of total Se). The metrological approach reported here could be considered as a pilot study in terms of metrological determination of SeMet in human serum, hence being suitable for method validation and inter-laboratory comparison.     

Simultaneous speciation of selenoproteins and selenometabolites in plasma and serum by dual size exclusion-affinity chromatography with online isotope dilution inductively coupled plasma mass spectrometry

A method for the simultaneous speciation of selenoproteins and selenometabolites in mouse plasma has been developed based on in series two-dimensional size exclusion and affinity high-performance liquid chromatography (2D/SE-AF-HPLC), using two columns of each type, and hyphenation to inductively coupled plasma-(quadrupole) mass spectrometry (ICP-QMS). The method allows the quantitative determination of selenoprotein P (SeP), extracellular glutathione peroxidase (eGPx), selenoalbumin (SeAlb), and selenometabolites in mouse plasma using species-unspecific isotope dilution (SUID). The 2D chromatographic separation is proposed to remove typical spectral interferences in plasma from chloride and bromide on ⁷⁷Se (⁴⁰Ar³⁷Cl) and ⁸²Se (⁸¹Br¹H). In addition, the approach increases chromatographic resolution allowing the separation of eGPx from Se metabolites of low molecular mass. The method is robust, reliable, and fast with a typical chromatographic runtime less than 20 min. Precision in terms of relative standard deviation (n?=?5) is in the order of 4 %, and detection limits are in the range of 0.2 to 1.0 ng Se g^?1. Method accuracy for determination of total protein bound to Se was assessed by analyzing human serum reference material (BCR-637) certified for total Se content, and latterly applied to mouse plasma (Mus musculus). In summary, a reliable speciation method for the analysis of eGPx, selenometabolites, SeP, and SeAlb in plasma/serum samples is proposed for the first time and is applicable to the evaluation of Se status in human in clinical studies and other mammals for environmental or toxicological assessment.

Determination of selenocysteine and selenomethionine in edible animal tissues by 2D size-exclusion reversed-phase HPLC-ICP MS following carbamidomethylation and proteolytic extraction

A method was developed for the simultaneous determination of selenomethionine (SeMet) and selenocysteine (SeCys) in meat (chicken and lamb muscles) and different offal tissues (heart, liver, kidney). The analytical procedure was based on the protein extraction with urea under reducing conditions (dithiothreitol), derivatization of SeCys and SeMet by carbamidomethylation with iodoacetamide (IAM) followed by quantitative proteolysis. The mixture of the derivatized Se-amino acids was purified by size-exclusion liquid chromatography (LC) and analysed by ion-paring reversed-phase HPLC–inductively coupled plasma mass spectroscopy (ICP MS). The quantification of SeCys and SeMet was carried out by the method of standard additions. ⁷⁷SeMet was used to control the SeMet derivatization efficiency and recovery. The method was validated by the determination of the Se mass balance. The Se-amino acids accounted for 91 ± 8% of the total selenium (mean of 95 samples of seven tissues analysed over a period of 18 months). The method was applied to the discrimination of the contribution of selenoproteins (containing SeCys) and other Se-containing proteins (containing SeMet) in tissues of animals during supplementation studies (dose–effect and tolerance).     

高效液相色谱-电感耦合等离子体质谱联用检测食品中的五种硒形态

建立了高效液相色谱-电感耦合等离子体质谱(HPLC-ICP-MS)联用检测硒酸盐(SeVI)、亚硒酸盐(SeIV)、硒代蛋氨酸(SeMet)、硒代胱氨酸(SeCys2)和硒代乙硫氨酸(SeEt)的方法。采用Hamilton PRP X-100色谱柱（250 mm×4.6 mm, 5 μm）,使用5 mmol/L的柠檬酸溶液(pH 4.5)作为流动相,电感耦合等离子体质谱(ICP-MS)检测,在21 min内可以完全分离5种硒形态。各形态硒的线性相关系数均大于0.9995, SeVI、SeIV、SeMet、SeCys2、SeEt的检出限分别为0.4、0.4、5.6、0.9、1.2 μg/L。探讨了不同提取方法的提取效果,鲜蘑菇和猪肉样品加标回收实验表明,对水溶性良好的无机硒和硒代蛋氨酸而言,采用柠檬酸溶液提取的效果非常好,SeIV和SeVI的回收率均在100%左右,SeMet的回收率为85.0%～95.3%;用蛋白酶水解提取,SeCys2和SeEt的回收率为79.9%～91.5%。该方法可完全满足食品中这5种硒形态的准确定量分析。     

Ionic liquids improved reversed-phase HPLC on-line coupled with ICP-MS for selenium speciation

Room-temperature ionic liquids (RTILs) improved reversed-phase high performance liquid chromatography (RP-HPLC) on-line combined with inductively coupled plasma mass spectrometry (ICP-MS) was developed for selenium speciation. The different parameters affecting the retention behaviors of six target selenium species especially the effect of RTILs as mobile phase additives have been studied, it was found that the mobile phase consisting of 0.4% (v/v) 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), 0.4% (v/v) 1-butyl-2,3-dimethylimidazolium tetrafluroborate ([BMMIM]BF₄) and 99.2% (v/v) water has effectively improved the peak profile and six target selenium species including Na₂SeO₃ (Se(IV)), Na₂SeO₄ (Se(VI)), l-selenocystine (SeCys₂), d,l-selenomethionine (SeMet), Se-methylseleno-l-cysteine (MeSeCys), seleno-d,l-ethionine (SeEt) were separated in 8 min. In order to validate the accuracy of the method, a Certified Reference Material of SELM-1 yeast sample was analyzed and the results obtained were in good agreement with the certified values. The developed method was also successfully applied to the speciation of selenium in Se-enriched yeasts and clover. For fresh Se-enriched yeast cells, it was found that the spiked SeCys₂ in living yeast cells could be transformed into SeMet. Compared with other ion-pair RP-HPLC-ICP-MS approaches for selenium speciation, the proposed method possessed the advantages including ability to regulate the retention time of the target selenium species by selecting the suitable RTILs and their concentration, simplicity, rapidness and low injection volume, thus providing wide potential applications for elemental speciation in biological systems.     

Speciation analysis of selenium in rice samples by using capillary electrophoresis-inductively coupled plasma mass spectrometry

An enzyme-assisted extraction used to extract all species of selenium in rice sample and a sensitive analytical method for the determination of ultratrace Se(VI), Se(IV), SeCys₂ (selenocystine) and SeMet (selenomethionine) with capillary electrophoresis-inductively coupled plasma mass spectrometry were firstly described in this study. The extraction method is simple, effective and can be used to extract trace selenium compounds in rice with high extraction efficiency and no altering its species. The analytical method has a detection limit of 0.1-0.9 ng Se/mL, and can be used to determine trace Se(VI), Se(IV), SeCys₂ and SeMet in rice directly without any derivatization and pre-concentration. With the help of above methods, we have successfully determined Se(VI), Se(IV), SeCys₂ and SeMet in selenium-enriched rice within 18 min with a recovery of 90-103% and a RSD (relative standard deviation, n = 6) of 3-7%. Our results indicated that selenium-enriched rice contained only one species of selenium, SeMet, and its concentration is in range of 0.136-0.143 μg Se/g dried weight. The proposed method providing a realistic approach for the nutritional and toxical evaluation of different selenium compounds in nutritional supplements.     

Determination of selenium in blood serum by inductively coupled plasma atomic emission spectrometry with pneumatic nebulization

The possibility of determining selenium in blood serum using inductively coupled plasma emission spectrometry with conventional pneumatic nebulization was studied. A high-resolution spectrometer (SBW=6 pm) with laterally viewed ICP was employed. Analysis with conventional pneumatic nebulization could overcome laborious and demanding digestion, which is necessary for hydride generation. A pressure digestion with nitric acid at 160 degrees C was sufficient to decrease the carbon content in the serum sample to 5%-10% of its original value. Spectral interference of the CN band was observed and mathematically corrected. It was found that the carbon-induced selenium line emission enhancement occurred even under ICP optimized conditions. A method of determination was developed and applied to the analysis of blood serum. True limit of detection in real samples is 0.01-0.02 mg/L and the limit of quantification (RSD 10%) is 0.03-0.07 mg/L using Se I 196.090 nm line at an integration time of 10-2 s. The method was tested by analysis of porcine blood serum and the serum reference material Seronorm MI 0181.     

Analytical Problems in Separation of Selenomethionine and Its Oxidative Product in HILIC HPLC

Selenomethionine (SeMet) is one of the main selenium forms in foods and supplements. Determining its presence in natural food samples creates difficulties due to possible oxidation processes. The objective of this study was to evaluate the possible degradation of SeMet in water extracts of green teas, one of the most consumed beverages worldwide. Such a medium has not been investigated at this time. The HILIC-HPLC MS/MS method with different stationary phases was used to achieve the satisfactory separation of SeMet and selenomethionine oxide (SeMetO). The addition of dithiothreitol and β-mercaptoethanol, recommended to ensure that SeMet is kept in the reduced form, was also evaluated. The best separation was achieved using the zwitterionic HILIC stationary phase coupled to mass spectrometry and MeOH with water (85/15, v/v) as the eluent. Extraction was done with hot water with the addition of β-mercaptoethanol. The infusions prepared from Lung-Ching teas (from the Zhejiang Province in China) contained the highest concentration of selenium in a typical cup of tea (12.5–17.3 µg L⁻¹). For other tested teas it decreased in the following order: Yunnan > Dilmah > Lipton. For Lung-Ching teas, the sum of concentrations of SeMet and SeMetO corresponded to about 46–63% of the total selenium in their extracts.     

Speciation of selenium in selenium-enriched shiitake mushroom, Lentinula edodes

The major selenium compound in an aqueous extract of the most popular mushroom in Eastern Asian countries, shiitake (Lentinula edodes), fortified with selenium (Se) was identified by means of hyphenated techniques, i.e. HPLC-inductively coupled argon plasma mass spectrometry and HPLC-electrospray ionization mass spectrometry (HPLC–ICP MS and HPLC–ESI MS). Sixty-eight per cent of the total Se in the selenized shiitake was extracted with water, and 49.8% of the Se in the water extract was eluted in the high molecular mass fraction (>40,000 kDa) before incubation at 37 °C. After incubation, 40.6% of the Se in the water extract was eluted in a lower molecular mass fraction and the Se eluted in the high molecular mass fraction had decreased to 14.0%, suggesting that the major selenium compound in the water extract was initially in a form bound to macromolecule(s) and was then enzymatically liberated from the macromolecule(s). The retention time of the liberated selenium compound in HPLC–ICP MS matched that of selenomethionine (SeMet), and the masses of molecular and fragment ions detected by HPLC–ESI MS also suggested that the selenium compound was SeMet. The selenized shiitake accumulated Se as SeMet, and SeMet might be bound to the water extractable high molecular mass protein(s).Electronic Supplementary Material Supplementary material is available for this article at     

Selenoproteins: the key factor in selenium essentiality. State of the art analytical techniques for selenoprotein studies

Selenium is an essential element for human health. The benefits of selenium are many including protection against cancer, heart diseases and other cardiovascular and muscle disorders. Selenium is also helpful in controlling gastrointestinal disorders, enhancing immunity of the human body and reducing age-related diseases. The health-promoting properties of Se are due to vital functions of selenoproteins in which selenium is present as selenocysteine, the 21st amino acid. To date, dozens of selenoprotein families have been described though many have roles that have not been fully elucidated. Selenoproteins research has attracted tremendous interest from different scientific areas. Analytical chemists have not remained indifferent to the attractive features of these unique proteins. Different analytical techniques, such as multidimensional chromatography–inductively coupled plasma mass spectrometry (ICPMS), electrospray (tandem) mass spectrometry (ESI-MS/MS), matrix-assisted laser desorption ionization time-of flight (MALDI-TOF) and sodium dodecyl sulphate polyacrylamide gel electrophoresis–laser ablation inductively coupled plasma mass spectrometry (SDS-PAGE-LA-ICPMS), have been applied to the determination of selenoproteins and selenium-containing proteins. This review describes the best-characterized selenoproteins to date in addition to the major contributions of analytical chemistry to the field of selenoproteins. The article also highlights the challenges of combining elemental and molecular mass spectrometry for the determination of selenoproteins and selenium-containing proteins.     

Determination of selenomethionine, selenocysteine, and inorganic selenium in eggs by HPLC–inductively coupled plasma mass spectrometry

A method for the simultaneous determination of selenomethionine (SeMet), selenocysteine (SeCys), and selenite [Se(IV)] in chicken eggs was developed. A sample preparation protocol including defatting, protein denaturation, and carbamidomethylation was optimized in order to achieve complete protein digestion and to avoid SeCys losses. Quantification was carried out by reversed-phase HPLC–inductively coupled plasma mass spectrometry (ICP MS) after quantitative isolation of the selenium-containing fraction by size-exclusion liquid chromatography. The detection limits were 0.06, 0.003, and 0.01 μg g⁻¹ (dry weight) for SeCys, Se(IV) and SeMet, respectively, and the precision was 5–10%. The end products of carbamidomethylation of the different selenium species were identified for the first time by electrospray QTOF MS after custom-designed 2D HPLC purification. Differences in selenium speciation in egg yolk and white were highlighted, the yolk containing more SeCys and the white more SeMet. An insight into selenium bioaccessibility in eggs was obtained by digestion with simulated gastric and gastrointestinal juices and size-exclusion HPLC-ICP MS.     

Comparison of analytical methods: ICP-QMS,ICP-SFMS and FF-ET-AAS for the determination of V,Mn, Ni,Cu, As,Sr, Mo,Cd and Pb in ground natural waters

Three analytical methods, namely, inductively coupled plasma sector field mass spectrometry (ICP-SFMS); inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and filter-furnace electrothermal atomic-absorption spectroscopy (FF-ET-AAS) for the determination of V, Mn, Ni, Cu, As, Sr, Mo, Cd and Pb in ground natural water samples were compared and evaluated for their capacity to provide reliable and precise results. Two certified reference materials (SLEW-3 Estuarine Water; SLRS-4 River Water) were analysed to prove that accurate results could be obtained by using all the listed methods with properly optimised parameters. The limit of detection (LOD) for V, Mn, Ni, Cu, As, Sr, Mo, Cd and Pb provided by the ICP-MS methods ranged from 0.001 to 0.05 µg L^?1. Such LOD proved sufficient for the reliable determination of the listed elements in ground natural waters. However, the LOD of the FF-ET-AAS was approximately two orders of magnitude higher than that of ICP-MS, which made it impossible to quantify V, Mn, Ni, Mo and Pb. The effects of the usage of the collision cell mode in ICP-QMS and of the desolvation system Apex for ICP-SFMS to eliminate oxide ions levels were investigated. For all three analytical methods, the influence of the matrix effect on the results of the determination of the investigated elements using matrix model solution, external calibration and standard addition methods was evaluated. A comparison using a paired Student’s t-test between the results obtained by both ICP-MS methods for V, Mn, Ni, Cu, As, Sr, Mo, Cd and Pb concentrations in ground natural waters showed that there was no significant difference on a 95% confidence level. The precision of the results for ICP-SFMS, ICP-QMS and FF-ET-AAS varied between ~0.5 and 11; 2.5 and 12.5; 3 and 13.5%, respectively. Moreover, ICP-SFMS equipped with the desolvation system APEX proved a better choice for As, Cu and Mn analysis due to its better LOD (0.008, 0.03 and 0.02 µg L^?1, respectively) and precision (S_r ≤ 5.0; 7.5; 9.0%, respectively) compared to ICP-QMS and FF-ET-AAS.     

Distribution and Dynamic Pathway of Selenium Species in Selenium-deficient Mice Injected with (82)Se-enriched Selenite

In order to elucidate Se metabolism in a living body, (82)Se-enriched selenite was injected intravenously into mice fed Se-adequate and -deficient diets. We studied the time-dependent changes in the distribution of the labeled Se in organs, red blood cells, and plasma. The total Se was determined by flow-injection ICPMS, and Se speciation analysis was conducted by micro-affinity chromatography coupled with low-flow ICPMS. Total Se in almost all organs, including liver, showed the maximum at 1 h after injection. From speciation analysis, exogenous (82)Se as Se-containing proteins other than selenoprotein P (Sel-P) (selenium containing albumin (SeAlb) and extra cellular glutathione peroxidase (eGPx)), peaked at 1 h and quickly decreased from 1 to 6 h after injection, whereas that as Sel-P, peaked at 6 h, and gradually decreased from 6 to 72 h after injection. We found that there were two pathways for the transfer of Se in mice; one was as SeAlb until 1 h after injection, and the other was as Sel-P from 6 to 72 h after injection.     

Fractionation of selenium-containing proteins in serum by multiaffinity liquid chromatography before size-exclusion chromatography–ICPMS

Immunoaffinity chromatography has been investigated for fractionation of serum into selenoalbumin and true selenoproteins. Among several albumin-depletion kits tested, a multiaffinity column specifically binding albumin and five other major serum proteins provided the best results. It extracted ca 95% of both albumin and selenoalbumin, which enabled interference-free determination of glutathione peroxidase, selenoprotein P, and selenoalbumin by size-exclusion chromatography combined with inductively coupled plasma mass spectrometry (SEC–ICPMS). The efficiency of the multiaffinity column did not vary over a period of 18 months. The purity of fractions separated by immunoaffinity LC was confirmed by elution-volume matching with standards in SEC–ICPMS and by selenopeptide mapping in capillary HPLC–ICPMS. Quantification of the selenium distribution among the different proteins in human serum from a control group and from a person on a selenium-rich diet revealed that 67% of the supplemented selenium was incorporated into albumin, 30% into glutathione peroxidase, and 3% into selenoprotein P.     

以蛋白质为基础模拟谷胱甘肽过氧化物酶

硒元素作为一种生命体中必须的微量元素,与人类的健康和疾病息息相关.硒元素主要以硒代半胱氨酸的形式存在于至少25种硒蛋白中,执行着多种生物功能.在这20多种硒蛋白中,谷胱甘肽过氧化物酶(GPx)作为一种主要的抗氧化酶,能够有效地利用谷胱甘肽还原氢过氧化物以防止机体的氧化损伤.这里,我们主要介绍以蛋白质为骨架构筑GPx模拟物的一些策略和方法,以期望于能够更好的理解硒蛋白的生物学性质,甚至开拓更为有效的技术去模拟这种抗氧化酶.     

HPLC-ICP-MS或HPLC-FAAS法分离测定硒化合物（英文）

 提出了一种用高效液相色谱（HPLC）分离和用电感偶合等离子体质谱仪（ICP－MS）或火焰原子吸收光谱仪（FAAS）作元素专一检测器在线测定硒的化学形态的方法。在优化的HPLC条件下,用ESAⅢ阴离子色谱柱（250mm×4．6mm）,以柠檬酸铵为流动相（5．5mmol／L,pH5．5,流速1．5mL／min）,进样量100μL,分离和测定三甲基硒离子、硒代蛋氨酸、亚硒酸和硒酸盐只需8min。HPLC－FAAS在线分析4种硒化合物的检测限为p（Se）=1mg／L。     

g-C3 N4 富集结合毛细管电泳与电感耦合等离子体质谱联用分析西瓜中硒形态

硒是人体所必需的微量元素之一,对人身体健康非常重要。该工作称取2.0 g三聚氰胺于反应釜中,在600℃下密闭加热2 h,冷却至室温,取0.5 g上述产物置于烧杯中在室温下超声10 h,静置30 min,取上层乳白色溶液于60℃下烘干,即得类石墨烯氮化碳（g-C₃ N₄ ）。所制备的g-C₃ N₄ 经傅里叶变换红外光谱（FT-IR）、X射线粉末衍射（XRD）、场发射环境扫描电子显微镜（SEM）进行表征,证明g-C₃ N₄ 已经成功合成。建立了毛细管电泳-电感耦合等离子体质谱（CE-ICP-MS）联用技术测定西瓜中硒形态的新方法。用胃蛋白酶作提取剂及超声波辅助提取西瓜中的硒形态,经g-C₃ N₄ 富集、长100 cm内径100 μm毛细管分离,电泳电压为22 kV,缓冲液为8 mmol/L NaH₂ PO₄ -12 mmol/L H₃ BO₃ -0.2 mmol/L十六烷基三甲基溴化铵（CTAB）（pH 9.2）,于11 min内完全分离6种硒形态。所建立的方法检测速度快、灵敏度高,采用CH₄ 作动态反应气消除干扰。硒脲（SeUr）、硒代胱氨酸（SeCys₂ ）、硒代蛋氨酸（SeMet）、亚硒酸钠（Se（Ⅳ））、硒酸钠（Se（Ⅵ））、硒代乙硫氨酸（SeEt）的线性范围（按Se计）分别为0.017~20 μg/L、0.091~50 μg/L、0.032~40 μg/L、0.023~60 μg/L、0.015~75 μg/L、0.015~30 μg/L。各硒形态的线性相关系数均大于0.9995,SeUr、SeCys₂ 、SeMet、Se（Ⅳ）、Se（Ⅵ）、SeEt的检出限分别为6.2、30、11、8.2、48、5.5 ng/L,回收率为96.0%~106%,RSD < 3%。将本方法应用于西瓜中硒形态分析,结果令人满意。     

Selenium and mercury bioaccessibility in fish samples: an in vitro digestion method

The assessment of hazard from selenium (Se) and mercury (Hg) contaminants in the food chain based on their potential bioaccessibility and on estimate of their actual content in fish is reported under an in vitro model. Atomic fluorescence spectroscopy (AFS) was applied for total selenium and mercury quantification. Selenium and mercury bioaccessibility varied depending on the type of fish analyzed. Se solubility in the gastrointestinal supernatants was higher in swordfish and sardine (76 and 83%, respectively) than in tuna (50%). A low Hg bioaccessibility (9-17%) was found for all the samples.Simulated human gastric and intestinal digestion led to the identification of selenomethionine (SeMet) and organic mercury in the three digested fish. Furthermore, these species were not modified during the digestion. Speciation of selenium compounds was done by liquid chromatography in conjunction with inductively coupled plasma mass spectrometry (LC-ICP-MS).Sardine had the most favorable Se:Hg, [Se:Hg]_{bioaccessible} and [SeMet:Hg]_{bioaccessible} molar ratios, making it preferable to tuna and swordfish.The effect of cooking was also evaluated.