High-performance liquid chromatography of selenoamino acids and organo selenium compounds. Speciation by inductively coupled plasma mass spectrometry

Multi-element Characteristics of Chinese Medical Baishao (Paeoniae Radix Alba) and Their Decoctions

Adopting ICP-AES and ICP-MS to determine the content of 53 elements (6 macro-elements, 47 trace elements), which used HNO₃ (5 mL) and H₂O₂ (2 mL) to digest Baishao (Paeoniae Radix Alba) by microwave. These herbs obtained from six producing areas in China, namely Xuanwu (Henan province), Shihezi (Xinjiang province), Zhongjiang (Sichuan province), Panan (Zhejiang province), Bozhou (Anhui province), and Heze (Shandong province). A certified reference material of Astragalus (GBW 10028, GSB-19) was used to assess the accuracy of the method. Except the slight change of Na and S in Xuanwu, the content of other producing areas followed the order of Ca > K > P > Mg > S > Na. The herbs of Shihezi (22,658 mg/kg) got the highest concentration of total elements, while the herbs of Panan (1.006 mg/kg) got the highest concentration of rare earth elements. The multi-element fingerprint map of Baishao was established, which was obviously different from other herbs. Meanwhile, the same method was adopted to determine the content of 50 elements in Baishao decoctions from three main producing areas. Compared with the herbs, each element was significantly reduced, and K was the highest concentration. The transfer rates of elements in Baishao decoctions followed the order (mean): As (55.79%) > Ni (55.19%) > Na (51.48%) > Mo (44.13%) > Ce (43.82%) > V (40.52%). The decoctions of Panan (0.122 mg/kg) got the highest content of rare earth elements. In all Baishao herbs and their corresponding decoctions, the levels of Cu, Cd, As, Pb, and Hg did not exceed the limits of the Green Trade Standards of Importing & Exporting Medicinal Plants & Preparations (WM2-2001) and Chinese Pharmacopoeia (2015).

In Situ Selective Measurement of SeIV in Waters and Soils: Diffusive Gradients in Thin-Films with Bi-Functionalized Silica Nanoparticles

The speciation of selenium (Se) controls its fate and behavior, determining both its biological and environmental activities. However, in situ monitoring of Se^IV presents a significant challenge due to its sensitivity to redox change. A novel diffusive gradients in thin films (DGT) technique containing mercapto-, amino-bifunctionalized SBA15 mesoporous silica nanoparticles was developed and evaluated in a series of laboratory and field deployment tests. The SBA-DGT exhibited a linear accumulation of Se^IV ( r² > 0.997) over a 72 h deployment, with negligible accumulation of Se^VI(<5%). Consistent prediction of Se^IV occurred within ionic strength and pH ranges of 0.1-200 mmol L^-1 and 3.6-8, respectively. Limits of detection of the SBA-DGT were 0.03 μg Se^IV L^-1, which is suitable for natural waters. Moreover, the properties of the bifunctionalized SBA15 enable it to be fabricated within ultrathin (0.05 mm) gel layers for use in conjunction with O₂ planar optode imaging. This new sandwich sensor technology with SBA-DGT was validated by mapping the two-dimensional distribution of Se^IV and oxygen simultaneously in rice rhizospheres. This study shows that SBA-DGT provides a selective measurement of Se^IV in situ, demonstrating its potential for both environmental monitoring and as a research tool for improving our understanding of Se biogeochemical processes.

A rapid and sensitive IC-ICP-MS method for determining selenium speciation in natural waters

Selenium (Se) is an element monitored by water quality agencies worldwide. The challenge of assessing its presence in aquatic systems is its low concentrations (parts per trillion) and the need for determining its chemical speciation. A method was developed using an ion chromatograph (IC) paired with a quadrupole inductively coupled plasma mass spectrometer (ICP-MS) equipped with a hydrogen reaction cell to provide analysts with a rapid and sensitive method to measure Se speciation with suitable accuracy and precision. The Se species selenite (SeIV) and selenate (SeVI) were separated within a 5 min span using dilute nitric acid as a mobile phase in a step-wise gradient (50–400 mmol L−1) and quantified using 80Se isotope that yielded low limits of detection (<10 ng L−1). Spectral interference from plasma generated diatomic argon ions (40Ar2+; m/z = 80) on 80Se was eliminated by hydrogen gas (H2) in the reaction cell. Polyatomic 79Br1H+ (m/z = 80) did not interfere with 80Se for quantification of common aquatic Se species (SeVI and SeIV) due to different column retention times. Two organic species (methylselenocysteine and selenomethionine) commonly found in aquatic and terrestrial plant tissues were also tested to rule out possible chromatographic interference and explore the potential application to biological samples. Urban rainwater and Canadian river water samples were analyzed for Se species to demonstrate the applicability of the method. Owing to its ability to rapidly determine Se species in water samples at environmentally relevant concentrations, the method may be useful for monitoring agencies to routinely measure Se species in freshwater aquatic systems.

Preparation and purification of organic samples for selenium isotope studies

Selenium (Se) is an important micronutrient but also a strong toxin with a narrow tolerance range for many organisms. As such, a globally heterogeneous Se distribution in soils is responsible for various disease patterns (i.e. Se excess and deficiency) and environmental problems, whereby plants play a key role for the Se entrance into the biosphere. Selenium isotope variations were proved to be a powerful tracer for redox processes and are therefore promising for the exploration of the species dependent Se metabolism in plants and the Se cycling within the Critical Zone. Plant cultivation setups enable systematic controlled investigations, but samples derived from them–plant tissue and phytoagar–are particularly challenging and require specific preparation and purification steps to ensure precise and valid Se isotope analytics performed with HG-MC-ICP-MS. In this study, different methods for the entire process from solid tissue preparation to Se isotope measurements were tested, optimized and validated. A particular microwave digestion procedure for plant tissue and a vacuum filtration method for phytoagar led to full Se recoveries, whereby unfavorable organic residues were reduced to a minimum. Three purification methods predominantly described in the literature were systematically tested with pure Se solution, high concentrated multi-element standard solution as well as plant and phytoagar as target matrices. All these methods efficiently remove critical matrix elements, but differ in Se recovery and organic residues. Validation tests doping Se-free plant material and phytoagar with a reference material of known Se isotope composition revealed the high impact of organic residues on the accuracy of MC-ICP-MS measurements. Only the purification method with no detectable organic residues, hydride generation and trapping, results in valid mass bias correction for plant samples with an average deviation to true δ^82/76Se values of 0.2 ‰ and a reproducibility (2 SD) of ± 0.2 ‰. For phytoagar this test yields a higher deviation of 1.1 ‰ from the true value and a 2 SD of ± 0.1 ‰. The application of the developed methods to cultivated plants shows sufficient accuracy and precision and is a promising approach to resolve plant internal Se isotope fractionations, for which respective δ^82/76Se values of +2.3 to +3.5 ‰ for selenate and +1.2 to +1.9 ‰ for selenite were obtained.

Selenium Speciation in the Fountain Creek Watershed (Colorado, USA) Correlates with Water Hardness, Ca and Mg Levels

The environmental levels of selenium (Se) are regulated and strictly enforced by the Environmental Protection Agency (EPA) because of the toxicity that Se can exert at high levels. However, speciation plays an important role in the overall toxicity of Se, and only when speciation analysis has been conducted will a detailed understanding of the system be possible. In the following, we carried out the speciation analysis of the creek waters in three of the main tributaries—Upper Fountain Creek, Monument Creek and Lower Fountain Creek—located in the Fountain Creek Watershed (Colorado, USA). There are statistically significant differences between the Se, Ca and Mg, levels in each of the tributaries and seasonal swings in Se, Ca and Mg levels have been observed. There are also statistically significant differences between the Se levels when grouped by Pierre Shale type. These factors are considered when determining the forms of Se present and analyzing their chemistry using the reported thermodynamic relationships considering Ca²⁺, Mg²⁺, SeO₄²⁻, SeO₃²⁻ and carbonates. This analysis demonstrated that the correlation between Se and water hardness can be explained in terms of formation of soluble CaSeO₄. The speciation analysis demonstrated that for the Fountain Creek waters, the Ca²⁺ ion may be mainly responsible for the observed correlation with the Se level. Considering that the Mg²⁺ level is also correlating linearly with the Se levels it is important to recognize that without Mg²⁺ the Ca²⁺ would be significantly reduced. The major role of Mg²⁺ is thus to raise the Ca²⁺ levels despite the equilibria with carbonate and other anions that would otherwise decrease Ca²⁺ levels.

Determination of seleno-amino acids bound to proteins in extra virgin olive oils

An analytical method has been developed to determine seleno-amino acids in proteins extracted from extra virgin olive oils (EVOOs). Different aqueous/organic solvents were tested to isolate proteins, an acetone:n-hexane combination being the best protein precipitant. In a first dimension chromatography, extracted proteins were analysed by size exclusion chromatography (SEC) coupled to inductively coupled plasma mass spectrometry (ICP-MS) to identify S and Se associations as proteins marker. Two fractions of 66 kDa (A) and 443 kDa (B) were identified. These fractions were submitted to microwave-assisted acid hydrolysis (MAAH) to release seleno-amino acids. In a second dimension chromatography seleno-amino acids were determined by reversed-phase chromatography (RPC) coupled to ICP-MS. Seleno-methylselenocysteine was determined with values ranging from 1.03-2.03±0.2 μg kg(-1) and selenocysteine at a concentration of 1.47±0.1 μg kg(-1). Variations of protein and seleno-amino acid concentrations were observed between EVOO varieties, contributing to EVOO cultivar differentiation.

Selenium and vitamin E for prostate cancer: post-SELECT (Selenium and Vitamin E Cancer Prevention Trial) status

Various formulations of selenium and vitamin E, both essential human dietary components, have been shown to possess a therapeutic and preventive effect against prostate cancer. Fortuitous results of clinical trials also implied a risk-reduction effect of selenium and vitamin E supplements. The Selenium and Vitamin E Cancer Prevention Trial (SELECT), using oral selenium and vitamin E supplementation in disease-free volunteers, was designed to test a prostate cancer chemoprevention hypothesis. SELECT was terminated early because of both safety concerns and negative data for the formulations and doses given. Here, we review and discuss the studies done before and since the inception of SELECT, as well as the parameters of the trial itself. We believe that there is a lack of appropriate in vivo preclinical studies on selenium and vitamin E despite many promising in vitro studies on these agents. It seems that the most effective doses and formulations of these agents for prostate cancer chemoprevention have yet to be tested. Also, improved understanding of selenium and vitamin E biology may facilitate the discovery of these doses and formulations.

Effect of selenium-enriched malt on VEGF and several relevant angiogenic cytokines in diethylnitrosamine-induced hepatocarcinoma rats

One hundred and ninety-three Sprague-Dawley (SD) rats (average body weight 100-120g) were randomly divided into five groups (I-V). Groups I and II rats served as the negative and positive controls respectively and both received 0.1mg/kg Se from sodium selenite supplemented diets for the 18-week experimental period. Groups III-V rats were fed Se from SEM supplemented diets (0.3, 1 and 3mg/kg respectively). To induce hepatocarcinoma, groups II-V rats received diethylnitrosamine solution (100mg/L) at the dosage of 10mg/kg body weight in drinking water daily for 16 weeks, followed by sterilized water for a further 2 weeks. Group I rats received sterilized water throughout. At weeks 4, 8, 12 and 16 five rats in each group were sacrificed by cervical decapitation. At the termination of the study, at week 18, the surplus rats were sacrificed by cervical decapitation. Feed was withheld from the rats for 12 h before sampling. The following items including TNF-alpha, IGF-II, NO and T-NOS levels in plasma were tested using kit techniques. At the same time the expression of vascular endothelial growth factor (VEGF) in tumor tissue was analyzed by immunohistochemistry using the envision two-step methods with a kit. The results indicated that SEM could increase the levels of TNF-alpha in the early stages of hepatocarcinoma formation, however there was a decrease in the later stage of hepatocarcinogenesis. SEM could also significantly decrease the levels of IGF-II and NO, and inhibit the expression of VEGF in tumor tissue. SEM delayed the development of hepatocarcinoma in rats and that could be partially attributed to inhibition of angiogenesis.

Selenium species in selenium-enriched and drought-exposed potatoes

The aim of this work was to study selenium (Se) speciation in the potato ( Solanum tuberosum L.) cultivar Desiree, enriched in Se by foliar spraying with a water solution containing 10 mg of Se/L in the form of sodium selenate. Four combinations of treatments were used: well-watered plants with and without Se foliar spraying and drought-exposed plants with and without Se foliar spraying. Water-soluble Se compounds were extracted from potato tubers by water or enzymatic hydrolysis with the enzyme protease XIV, amylase, or a combination of protease XIV and amylase. Extraction was performed using incubation at a constant temperature and stirring (37 degrees C at 200 rpm) or by ultrasound-assisted extraction (300 W), using different extraction times. Separation of soluble Se species (SeCys2, SeMet, SeMeSeCys, selenite, and selenate) was achieved by ion-exchange chromatography, and detection was performed by inductively coupled plasma-mass spectrometry (ICP-MS). Results showed that the concentration of selenate extracted was independent of the enzymatic extraction technique (approximately 98 ng/g for drought-exposed and 308 ng/g for well-watered potato tubers), whereas the extraction yield of SeMet changed with the protocol used (10-36%). Selenate and SeMet were the main soluble Se species (representing 51-68% of total Se) in potato tubers, regardless of the growth conditions.

Food-chain selenium and human health: spotlight on speciation

There is a growing appreciation that it is not just the total intake of dietary Se that is important to health but that the species of Se ingested may also be important. The present review attempts to catalogue what is known about Se species in foods and supplements and the health effects in which they are implicated. The biosynthetic pathways involved in Se assimilation by plants and the way in which Se species are metabolised in animals are presented in order to give an insight into the species likely to be present in plant and animal foods. Known data on the species of Se in the food chain and in food supplements are tabulated along with their concentrations and the analytical methodology used. The latter is important, since identification that is only based on retention-time matching with authentic standards must be considered as tentative: for evidence of structural confirmation, fragmentation of the molecular ion in addition to MS data is required. Bioavailability, as normally defined, is higher for organic Se species. Health effects, both beneficial and toxic, thought to be associated with specific Se species are described. Potent anti-tumour effects have been attributed to the low-molecular-weight species,Se-methyl-selenocysteine and its γ-glutamyl-derivative, found in a number of edible plants of theAlliumandBrassicafamilies. There remain considerable gaps in our knowledge of the forms of Se that naturally occur in foods. Without adequate knowledge of Se speciation, false conclusions may be drawn when assessing Se requirements for optimal health.

Speciation of selenium in a commercial dietary supplement by liquid chromatography coupled with inductively coupled plasma-mass spectrometry (ICP-MS)

Size exclusion and anion-exchange chromatographies coupled with inductively coupled plasma-mass spectrometry (ICP-MS) were used for the speciation of selenium (Se) in a dietary supplement. A sequential extraction method resulted in 85% recovery of Se and 78% of the Se extracted could be identified. The results obtained show that selenomethionine and its oxide are the predominant compounds, while selenite and selenomethylcysteine are present at low concentrations. Methane seleninic acid, probably arising from the oxidation of selenomethylcysteine, accounted for 22% of total Se. High-molecular-weight compounds, probably proteins, were detected in sodium dodecyl sulfate (SDS) and driselase extracts by size exclusion chromatography.

New separation method for organic and inorganic selenium compounds based on anion exchange chromatography followed by inductively coupled plasma mass spectrometry

We describe a new method for separating the organic and inorganic selenocompounds methaneseleninic acid, selenite, selenate, methylselenocysteine, selenocystine as well as both selenomethionine and its oxidized form. The separation is performed on a Hamilton PRP-X100 column. According to the literature, the oxidized form of selenomethionine-which is easily formed-is eluted close to the dead volume when this column is used. The choice of parahydroxybenzoic acid as mobile phase enabled us to elute all of these species after this oxidized form, resulting in better identification and quantification. The factors determining separation (eluent concentration, pH, gradient) were optimized via an experimental design. Application of the method to yeast and commercial tablets showed that the principal Se compound present was selenomethionine, which was also present in its oxidized form.

Selenium speciation by high-performance anion-exchange chromatography–post-column UV irradiation coupled with atomic fluorescence spectrometry

A technique for the speciation of selenomethylcysteine (SeMeCys), selenocystine (SeCys), selenite [Se(IV)] and selenomethionine (SeMet) was established in this paper using high-performance anion-exchange chromatography coupled with atomic fluorescence spectrometry (HPAEC-AFS). Analytes were separated on an AminoPac PA10 column and then digested by on-line ultraviolet (UV) irradiation, which destroyed organic compound structure. Hydride generation was used as an available sample introduction technique for atomic fluorescence detection. The detection limits of four compounds were 1-5 microg/L (250 microL injection, 10 times of the baseline noise). The relative standard deviations (RSDs), calculated from seven consecutive injections of 100 microg/L standard mixtures, were from 2 to 4%. Selenious yeast tablet, which had been proposed as selenium supplement, and human urine collected from a volunteer were analyzed. Good spiked recoveries from 86 to 103% were obtained.

Direct amino acid analysis method for speciation of selenoamino acids using high-performance anion-exchange chromatography coupled with integrated pulsed amperometric detection

Speciation analysis of selenomethylcysteine (SeMeCys), selenomethionine (SeMet) and selenocystine (SeCys) has been performed using a direct amino acid analysis method with high-performance anion-exchange chromatography (HPAEC) coupled with integrated pulsed amperometric detection (IPAD). Three selenoamino acids could be baseline-separated from 19 amino acids using gradient elution conditions for amino acids and determined under new six-potential waveform. Detection limits for SeMeCys, SeMet and SeCys were 0.25, 1 and 20 microg/L (25 microL injection, 10 times of the baseline noise), respectively. The relative standard deviations (RSDs) of 200 microg/L SeMeCys, SeMet and SeCys were 3.1, 4.1 and 2.8%, respectively (n=9, 25 microL injection). The proposed method has been applied for determination of selenoamino acids in extracts of garlic and selenious yeast granule samples. No selenoamino acids were found in garlic. Both SeMet and SeCys were detected in selenious yeast tablet with the content of 45 and 129 microg Se/g, respectively. Selenoamino acids standards were spiked in garlic and yeast granule samples and the recovery ranged from 90 to 106%.

Selenium speciation analysis using inductively coupled plasma-mass spectrometry

Selenium exists in several oxidation states and a variety of inorganic and organic compounds, and the chemistry of selenium is complex in both the environment and living systems. Selenium is an essential element at trace levels and toxic at greater levels. Interest in speciation analysis for selenium has grown rapidly in this last decade, especially in the use of chromatographic separation coupled with inductively coupled plasma-mass spectrometry (ICP-MS). Complete characterization of selenium compounds is necessary to understand selenium's significance in metabolic processes, clinical chemistry, biology, toxicology, nutrition and the environment. This review describes some of the essential background of selenium, and more importantly, some of the currently used separation methodologies, both chromatographic and electrophoretic, with emphasis on applications of selenium speciation analysis using ICP-MS detection.

Seleno-compounds in garlic and onion

Garlic (Allium sativum) and onion (Allium cepa) are widely known for their biological properties but are far from having revealed all of their secrets even if the compounds involved in the biological mechanisms, flavenols, sulphur and seleno compounds have been identified. The beneficial effect of garlic on health including protection against cardiovascular diseases and cancers results from all of these compounds although their individual involvement is complex. Garlic and onion, broccoli, wild leek, have the ability to accumulate the selenium (Se) from soil. These Se-enriched plants present a greater protection against carcinogenesis than the common plants and two Se-compounds possessing anti-cancer activity have been identified: Se-methyl selenocysteine and gamma-glutamyl-Se-methyl selenocysteine. However, several Se-compounds from Se-enriched garlic or onion remain unidentified. The techniques for the detection of Se-species are numerous but few methods are able to identify the detected compounds. The very small quantities of Se-compounds present and the clear lack of standards do not make their analysis straightforward, particularly for non-enriched samples. Over the last 10 or so years development of the synthesis of Se-compounds and the use of GC-AED or EC/HPLC-ICP-MS have shown considerable possibilities. These techniques have allowed advances in the identification of Se-compounds, some of which are analogues of S-compounds in plants and yeasts. When these techniques are coupled to EC/HPLC-APCI-MS-MS, they provide a lot of information about the Se-biosynthesis in garlic. This has allowed the preferential formation of methylated compounds in Se-biochemistry to be identified, in contrast to the sulphur biochemistry of the Allium spp. in which compounds containing propenylic groups predominate. This review focuses on the recent advances in the analytical methods of Se-compounds in garlic and onion and particular attention is given to the biological properties of Se-species identified in Se-enriched plants.

Effect of selenium-enriched malt on hepatocarcinogenesis, paraneoplastic syndrome and the hormones regulating blood glucose in rats treated by diethylnitrosamine

233 SD rats weighing 100 approximately 120 g were divided randomly into 6 groups. The animals in group I and group II received 0.1 mg/kg selenium in the form of sodium selenite only and served as the negative control and positive control, respectively. Animals in groups III, IV and V were fed with selenium as Se-enriched malt supplemented diets (0.3, 1 and 3 mg/kg), and group VI with selenium by using sodium selenite supplemented diets (3 mg/kg). Animals of groups II approximately VI were induced hepatoma by diethylnitrosamine (100 mg/l) for 16 weeks, then drunk with sterilized water for 2 more weeks. Subsequently, the effects of Se-enriched malt and sodium selenite on hepatoma nodules, relative liver weight, the liver function indices including alanine aminotransferase (ALT), alkaline phosphatase (ALP), albumin (ALB), total bilirubin (TBIL), and the tumor markers, named as gamma-glutamyltranspeptidase (GGT), alpha-fetoprotein (AFP), insulin-like growth factor-II (IGF-II) were recorded. The calcium concentration, glucose content in plasma and values of the hormones regulating blood glucose, such as insulin, glucagons and thyroid hormones (3,5,3'-tetraiodothyronine, T(3); 3,5,3'5'-tetraiodothyronine, T(4)) were observed as well. At the same time, the correlations between the concentration of plasma glucose and related hormones were also analyzed. The results indicated that Se-enriched malt showed a better chemopreventive efficiency in decreasing the number of hepatoma nodules, relative liver weight and the contents of AFP, GGT, IGF-II, ALT, ALP and TBIL in the plasma, and delaying the descent of hormones in the serum, names as insulin, glucagons, T(3) and T(4) than those feeding with sodium selenite. Effect of Se-enriched malt excelled sodium selenite in the aspects of deadening the descent of glucose concentration in the plasma and the rise of calcium concentration in the serum of the rats with hepatoma induced by diethylnitrosamine. The values of glucose and calcium were significantly related to those items fore-named. In conclusion, the function of Se-enriched malt in deadening the lesion and delaying the development of hepatoma of rats induced by diethylnitrosamine was better than that of sodium selenite. Hypoglycemia and hypercalcemia were significantly correlated with the multifactors mentioned above.

Cultivation conditions and selenium fertilization alter the phenolic profile, glucosinolate, and sulforaphane content of broccoli

Broccoli is a food often consumed for its potential health-promoting properties. The health benefits of broccoli are partly associated with secondary plant compounds that have bioactivity; glucosinolates and phenolic acids are two of the most abundant and important in broccoli. In an effort to determine how variety, stress, and production conditions affect the production of these bioactive components broccoli was grown in the greenhouse with and without selenium (Se) fertilization, and in the field under conventional or organic farming procedures and with or without water stress. High-performance liquid chromatography/mass spectrometry was used to separate and identify 12 primary phenolic compounds. Variety had a major effect: There was a preponderance of flavonoids in the Majestic variety, but hydroxycinnamic esters were relatively more abundant in the Legacy variety. Organic farming and water stress decreased the overall production of phenolics. Se fertilization increased glucosinolates in general, and sulforaphane in particular, up to a point; above that Se fertilization decreased glucosinolate production. Organic farming and water stress also decreased glucosinolate production. These data show environmental and genetic variation in phenolics and glucosinolates in broccoli, and warn that not all broccoli may contain all health-promoting bioactive components. They further show that selection for one bioactive component (Se) may decrease the content of other bioactive components such as phenolics and glucosinolates.

Current mass spectrometry strategies for selenium speciation in dietary sources of high-selenium

This document reviews the most relevant mass spectrometry approaches to selenium (Se) speciation in high-Se food supplements in terms of qualitative and quantitative Se speciation and Se-containing species identification, with special reference to high-Se yeast, garlic, onions and Brazil nuts. Important topics such as complexity of Se speciation in these materials and the importance of combining Se-specific detection and molecule-specific determination of the particular species of this element in parallel with chromatography, to understand their nutritional role and cancer preventive properties are critically discussed throughout. The versatility and potential of mass spectrometric detection in this field are clearly demonstrated. Although great advances have been achieved, further developments are required, especially if "speciated"certified reference materials (CRMs) are to be produced for validation of measurements of target Se-containing species in Se-food supplements.

Selective detection and identification of Se containing compounds—review and recent developments

The complexity of selenium (Se) chemistry in the environment and in living organisms presents broad analytical challenges. The selective qualitative and quantitative determination of particular species of this element is vital in order to understand selenium's metabolism and significance in biology, toxicology, clinical chemistry and nutrition. This calls for state-of-the-art analytical techniques such as hyphenated methods that are reviewed with particular emphasis on interfaced separation with element-selective detection and identification of the detected selenium compounds. Atomic spectral element specific detection for monitoring chromatographic eluent enabled quantitative determination of selenium species in selenized yeast and qualitative measurement for breath samples. Gas chromatography with atomic emission detection (AED) of ethylated species and fluoroacid ion pair HPLC applied to the analysis of currently produced or archived selenized yeast and Brassica juncea have revealed the presence of a previously unrecognised Se-S amino acid, S-(methylseleno)cysteine.

The nutritional significance, metabolism and toxicology of selenomethionine

SeMet is a naturally occurring toxic amino acid but at the same time represents the major nutritional source of selenium for higher animals and humans. The ability of SeMet to be incorporated into the body proteins in place of Met furthermore provides a means of reversible Se storage in organs and tissues. This property is not shared by any other naturally occurring selenoamino acid and thus could be associated with a specific physiological function of SeMet. Since higher animals cannot synthesize SeMet, yet from it all needed forms of Se are produced, SeMet meets the criteria of an essential amino acid. Accordingly, SeMet, or enriched food sources thereof, are appropriate forms of Se for human nutritional Se supplementation. However, while SeMet or Se yeast are already widely used in over-the-counter nutritional supplements, infant formulas and parenteral feeding mixtures still contain Se in the form of sodium selenate or sodium selenite, even though these are not the normal nutritional forms of Se. In animal nutrition, these inorganic selenium salts are increasingly replaced by food sources of SeMet such as Se yeast. Synthetic SeMet could also be employed as a feed additive, but its regulatory status is as yet undetermined. The optimal nutritional levels of SeMet for different animal species still need to be determined. The expectation is that lower additions to feedstock of equivalent levels of SeMet will suffice to achieve adequacy than currently approved maximum levels of Se in the form of inorganic Se salts.

Simultaneous determination of selenium and antimony compounds by capillary electrophoresis with indirect fluorescence detection

Capillary electrophoresis (CE) with indirect fluorescence detection was used to analyze selenium (selenite, selenate, selenomethionine, and selenocystine) and antimony (antimonite and antimonate) compounds. The separation was achieved by CE in 6 min with a 1.2 mM fluorescein solution at pH 9.5. Fluorescein also functioned as a background fluorophore for the indirect detection of these nonfluorescent species. Linearity of more than two orders of magnitude was generally obtained. Precision of migration times and peak areas was less than 1.0% and 7.2%, respectively. The concentration limits of detection (CLODs) was in the microM range. The detection sensitivity was generally dependent upon the transfer ratio (TR, defined as the number of moles of fluorescein ions displaced by one mole of analyte ions) of each species.

Selenocompounds in plants and animals and their biological significance

There are several selenocompounds in tissues of plants and animals. Selenate is the major inorganic selenocompound found in both animal and plant tissues. Selenocysteine is the predominant selenoamino acid in tissues when inorganic selenium is given to animals. Selenomethionine is the major selenocompound found initially in animals given this selenoamino acid, but is converted with time afterwards to selenocysteine. Selenomethionine is the major selenocompound in cereal grains, grassland legumes and soybeans. Selenomethionine can also be the major selenocompound in selenium enriched yeast, but the amount can vary markedly depending upon the growth conditions. Se-methylselenocysteine is the major selenocompound in selenium enriched plants such as garlic, onions, broccoli florets and sprouts, and wild leeks.

Speciation of arsenic and selenium compounds by ion-pair reversed-phase chromatography with electrothermic atomic absorption spectrometry. Application of experimental design for chromatographic optimisation

An off-line system is proposed consisting of ion-pair reversed-phase liquid chromatography, collections of fractions at the outflow of the column and furnace atomic absorption spectrometry. The so-called system allowed determination of both arsenic and selenium species mainly found in the environment and in mammals (arsenite, arsenate, monomethylarsonate, dimethylarsinate, selenite, selenate, selenocystamine, selenocystine, selenomethionine and selenoethionine). In order to study the retention behaviour of these compounds and to estimate the optimal conditions for the chromatographic separation, central composite designs were used to evaluate the influence of the eluent parameters such as pH, tetrabutylammonium phosphate (TBA) concentration and sodium hydrogenphosphate amounts. The retention factors of each species and the selectivity were established as response criteria. Response surfaces and isoresponse curves were drawn from the mathematical models and enabled one to determine the optimal conditions and to visualise the method robustness. The predicted optimal zone was situated at pH 5.5-6.5, 4.0 mM Na2HPO4 and 3.0-4.0 mM TBA. Regression models suggested linearity for the studied compounds in the range 25-200 microg selenium and arsenic per litre investigated.

Hybridation of different chiral separation techniques with ICP-MS detection for the separation and determination of selenomethionine enantiomers: chiral speciation of selenized yeast

Enantioseparation and determination of selenomethionine enantiomers in selenized yeast was investigated using chiral separation techniques based on different principles, coupled on-line to inductively coupled plasma mass spectrometry (ICP-MS) for selenium-specific detection. High performance liquid chromatography (HPLC) on a beta-cyclodestrin (beta-CD) column, cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC), gas chromatography (GC) on a Chirasil-L-Val column, and HPLC on a Chirobiotic T column have been investigated as the chiral separation techniques. For HPLC separation on the beta-CD column, and also for CD-MEKC, selenomethionine enantiomers were derivatized with NDA/CN(-). For chiral separation by GC, selenomethionine enantiomers were converted into their N-trifluoroacetyl (TFA)-O-alkyl esters. The developed hybridation methodologies are compared with respect to enantioselectivity, sensitivity and analysis time. The usefulness of the best-suited method [HPLC (Chirobiotic T)-ICP-MS] was demonstrated by its application to the successful chiral speciation of selenium and D-and L-selenomethionine content determination in selenized yeast.

The protective role of selenium on genetic damage and on cancer

Collectively, results from epidemiologic studies, laboratory bioassays, and human clinical intervention trials clearly support a protective role of selenium against cancer development. Several hypotheses have been proposed to explain these observations. Increased genomic instability, either inherent or induced by exogenous agents (mutagens or carcinogens), has been considered as a primary event leading to neoplastic transformation. This report deals specifically with the evidence for a role of selenium in the inhibition of carcinogen-induced covalent DNA adduct formation and retardation of oxidative damage to DNA, lipids and proteins, and for modulating cellular and molecular events that are critical in cell growth inhibition and in the multi-step carcinogenesis process. At present, the bulk of our knowledge on the role of selenium on genetic stability is based primarily on animal data and from studies conducted in in vitro systems. Studies performed in vitro showed that the dose and form of selenium compounds are critical factors with regard to cellular responses. Inorganic (at doses up to 10microM) and organic selenium compounds (at doses equal to or greater than 10microM) elicit distinctly different cellular responses. The recommended daily allowance (RDA) is 50-70 microgramSe per day for healthy adults; with 40 microgramSe as minimum requirement. Less than 11 microgramSe will definitely put people at risk of deficiency that would be expected to cause genetic damage. Daily doses of 100-200 microgramSe inhibited genetic damage and cancer development in humans. About 400 microgramSe per day is considered an upper limit. Clearly, doses above the RDA are needed to inhibit genetic damage and cancer. However, it has been hypothesized that the intake of excessive doses of selenium may cause oxidative damage, leading to genomic instability. The use of a cocktail consisting of selenium, and other vitamins and minerals appears to be a promising approach to inhibit genetic damage and the development of cancer. It is the author's recommendation that development of mechanism-based hypotheses that can be tested in pilot studies in different populations prior to a large-scale clinical trial in humans, is of paramount importance in order to better understand the role of selenium on genetic stability and cancer.

Separation and identification of organic and organometallic compounds by use of a liquid chromatography–particle beam-glow discharge mass spectrometry combination

Evaluation of the particle beam glow discharge mass spectrometry (PB-GDMS) system as a detector for liquid chromatography (LC) is described for the analysis of polycyclic aromatic hydrocarbons, steroids, selenoamino acids, and alkyllead compounds. A particle beam interface is used to introduce analyte species from the LC into a glow discharge source for subsequent vaporization and ionization. Mass spectra display classic EI fragmentation patterns for the organic compounds, as well as elemental and molecular information for the organometallic compounds. Chromatographic separations display good temporal correlation between UV and PB-GDMS detection modes. Detection limits for Pb in lead nitrate, triethyllead, and triphenyllead fall in the sub-ppb (ng) range.

High-performance liquid chromatography of selenium compounds utilizing perfluorinated carboxylic acid ion-pairing agents and inductively coupled plasma and electrospray ionization mass spectrometric detection

Increasing speciation demands in clinical chemistry, toxicology and nutrition have made the determination of the total elements in a sample inadequate; the amount of an element and the chemical forms in which it is present need to be known. Inductively coupled plasma mass spectrometry (ICP-MS) was used after high-performance liquid chromatographic (HPLC) separation, as was electrospray ionization mass spectrometry (ESI-MS). The effect of variation of the number of carbon atoms in perfluorinated carboxylic acids used as ion-pairing agents for the separation of selenium compounds was examined. Trifluoroacetic acid (0.1%), pentafluoropropanoic acid (0.1%) or heptafluorobutanoic acid (0.1%; HFBA) were alternatively used as additives to methanol-water (1:99, v/v) solutions as mobile phases. Reversed-phase HPLC-ICP-MS with 0.1% HFBA in the mobile phase allowed more than 20 selenium compounds to be separated in 70 min in an isocratic elution mode; the separation of natural selenium-enriched sample extracts was examined and explained. The pH of the 0.1% HFBA solution was modified with hydrochloric acid or ammonia and the pH of the sample extracts before injection was modified in order to overcome unwanted double peak formation in the chromatograms of sample extracts. Oxidations of standard gamma-glutamyl-Se-methylselenocysteine and Se-methylselenocysteine were carried out using 30% H2O2 solution and identifications of selenium-containing oxidation products were made using HPLC-ICP-MS and HPLC-ESI-MS. The principal organic oxidation product in both cases was methaneseleninic acid (MeSeO2H).

Identification of the zinc-binding protein specifically present in male rat liver as carbonic anhydrase III

A zinc (Zn)-binding protein that is present specifically in the livers of male adult rats was detected by HPLC with in-line detection by mass spectrometry (ICP MS). The Zn-binding protein was purified on Sephadex G-75 and G3000SW HPLC columns. and was identified as carbonic anhydrase III (CAIII) based on the amino acid sequence of a peptide obtained on lysyl endopeptidase digestion. CAIII is expressed as one of the major Zn-binding proteins in the livers of male rats in an age-dependent manner, a comparable amount of Zn to that of copper, Zn-superoxide dismutase (Cu,Zn-SOD) being bound to CAIII at 8 weeks of age. Castration at 4 or 8 weeks of age was shown to reduce Zn bound to CAIII to 47.5% of the sham-operated control level, suggesting that the sex-dependent expression of CAIII is partly regulated by a sex hormone, androgen. The concentration of CAIII in the livers of Long-Evans rats with a cinnamon-like coat color (LEC rats), an animal model of Wilson disease, was also estimated as Zn bound to CAIII and shown to be lower than that in Wistar rats before the onset of hepatitis. The concentration of CAIII was decreased specifically by repeated injections of cupric ions without the Cu,Zn-SOD concentration being affected.

Use of an ion-pairing reagent for high-performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry determination of anionic anticoagulant rodenticides in body fluids

The on-line combination of high-performance liquid chromatography with mass spectrometry (HPLC-MS) has become a powerful tool for trace analysis thanks to the developments in interface techniques. However, non-volatile salts such as ion-pairing reagents are considered to be incompatible with HPLC-MS systems; they cause drops in analyte signals because of contamination of mass analyzers and also because of blocking of the capillary transferring ions from atmospheric pressure to the vacuum manifold. In this work, a new type of ion-pairing reagent, di-n-butylammonium acetate (DBA), was evaluated for use in HPLC-MS. DBA did not cause these problems to HPLC-MS systems; a possible explanation might be that DBA decomposed to volatile compounds under APCI conditions. In addition, DBA was very useful for obtaining sharp peaks, which resulted in high sensitivity. With this ion-pairing reagent, we developed a procedure for the measurement of five (including internal standard) anticoagulant rodenticides in whole blood and urine samples by SIM detection of [M-H]- ions. Calibration range, recoveries and precision of the method were examined; detection limits as low as 1-5 ng/ml blood sample or 0.5-2.5 ng/ml urine sample were achieved.