Determination Of Total Se Research Articles

Sensitive method for total selenium determination in garlic and nuts by UV–photochemical vapor generation coupled to atomic absorption spectrometry using mild conditions

Photochemical vapor generation (PVG) coupled on–line to atomic absorption spectrometry using a flow injection mode was investigated for the determination of total Se in garlic and nut samples. In the presence of low molecular weight organic acid solutions, Se(IV) is converted by UV irradiation to volatile species which are transported to the heated quartz tube atomizer. Formic and acetic acids were tested as photochemical reagents and a mixture of 1.5 % (v/v) formic and 5 % (v/v) acetic acid was the best alternative. Central composite design was employed for parameters optimization. The effect of potential interfering elements such as hydride–forming elements, transition metals and nitric acid was investigated to ascertain possible effects of the matrix on Se(IV) signal. Under optimized conditions a detection limit (LOD) of 33 ng g–1 (3σ) was reached. Samples of garlic and nuts purchased at a local market were analyzed and Se concentrations spanned the range 0.36–248 µg g–1. These results were compared with ICP–MS measurements utilizing an elliptical joint confidence region (EJCR) with bilinear least squares analysis, and good results were obtained.

Sensitive analysis of selenium speciation in natural seawater by isotope-dilution and large volume injection using PTV-GC-ICP-MS

Although oceans play a key role in the global selenium (Se) cycle, there is currently very little quantitative information available on the distribution of Se concentrations and Se speciation in marine environments. In general, determining Se concentration and speciation in seawater is highly challenging due to very low Se levels ((sub)ng⋅L−1), whereas matrix elements interfering Se pre-concentration and detection are up to the g⋅L−1 levels. In this study, we established a sensitive method for the determination of the various Se chemical fractions present in natural seawater, i.e. selenite (SeIV), selenate (SeVI), organic Se-II + Se0 and total Se, using species-specific isotope dilution gas chromatography coupled to inductively coupled plasma mass spectrometry (ID-GC-ICP-MS). We compared different derivatization reagents and optimized specific pre-treatment protocols, including a microwave assisted oxidation protocol for the determination of total Se and organic Se-II + Se0 using H2O2. To increase sensitivity, we developed an online pre-concentration method based on large volume injection (LVI) using a programmed temperature vaporization (PTV) inlet. Eventually, the developed method achieved low absolute and methodological detection limits, i.e., respectively, 0.1–0.3 pg and 0.9–3.1 ng.L-1 for the different fractions. The accuracy of our method was of 2% for a certified reference material (CRM) diluted in artificial seawater while the precision was better than 4% for a freshwater CRM in artificial seawater matrix as well as two common seawater CRMs certified for trace elements excluding Se. As a proof-of-concept, we quantified the various Se fractions in a large number of natural water samples from the Baltic and North Seas, encompassing a wide range of salinity (7–35 psu), which shows that its detection limits are sufficient to determine total Se, SeIV, SeVI and organic Se-II + Se0 concentrations in brackish and marine systems.

Determination of Se content of 78 sesame accessions with different geographical origin

Selenium (Se) is an essential trace element for human health and plays an important role in fundamental physiological functions. Se accumulates in sesame seeds and this situation may differ between genotypes. Determination of Se content in food is very important because there is a narrow margin of safety between an adequate amount and overconsumption. The purpose of this study was to evaluate the variability in Se content among different sesame accessions from Turkey (12 sesame accessions) and 22 other countries from four continents (Asia, Africa, Europe and America). The determination of total Se in seed was performed with an atomic absorption spectrometer. The Se content of sesame seeds samples exhibited a wide range i.e. 0–9.32 mg kg−1, with an average value of about 2.29 mg kg−1. The accession India 1 had the highest Se concentration. The mean Se contents of sesame from 23 countries varied between 0.24–8.31 mg kg−1 and with an average value of about 2.29 mg kg−1. Sesame breeders can use the results of the present study to further the breeding programs for the development of new biofortified varieties.

A simple sample preparation procedure for the fast screening of selenium species in soil samples using alkaline extraction and hydride-generation graphite furnace atomic absorption spectrometry

This work proposes a simple procedure for the determination of selenium species in soil samples using an ultrasound-assisted alkaline extraction and hydride generation atomic absorption spectrometry (HG AAS), which is known to be specific for the determination of Se(IV) only. The hydride was trapped and atomized in a graphite tube furnace (GF) coated with iridium as a permanent chemical modifier. The limits of detection and quantification for the developed method were 6μgL−1 and 20μgL−1 Se(IV), respectively, with a linear range between 20 and 100μgL−1, and a linear coefficient of R=0.999. The total Se content in the samples was determined in the alkaline extract using high-resolution continuum source GF AAS (HR-CS GF AAS), and the content of Se(VI) was determined by difference between the total Se and the content of Se(IV). The extraction efficiency was verified by comparing the results obtained by the alkaline extraction and by direct solid sample analysis using HR-CS GF AAS. The accuracy of the method for total Se determination was ascertained using microwave-assisted acid digestion as well as direct solid sample analysis by HR-CS GF AAS of the certified reference materials MURST-ISS-A1 (Antartic marine sediment) and BCR 142R (light sandy soil), and soil samples from different regions of Brazil.

Speciation of Chromium(VI) and Selenium(IV and VI) by High-Performance Liquid Chromatography–Fluorometric Detection Using 2,3-Diaminonaphthalene as a Single Derivatizing Reagent

Abstract A speciation method for chromate, selenite, and selenate was developed by high-performance liquid chromatography (HPLC)–fluorometric detection (FL) using a single derivatizing reagent. Chromium(VI) was determined based on the fluorescence intensity of 1H-naphtho[2,3-d][1,2,3]triazole (NAT) derived from 2,3-diaminonaphthalene (DAN) and nitrous ion; the NO2− was generated through a redox process between Cr(VI) and hydroxylamine hydrochloride (HACl). 4,5-Benzopiazselenol (Se-DAN) was also derived from Se(IV) and DAN, and it was resolved from NAT and detected by reversed-phase HPLC–FL operated under a single setting of an excitation and a fluorescence wavelength. Linear ranges of the calibration curve and detection limits were 0–20 µmol L−1 (correction coefficient: 0.995) and 0.1 µmol L−1 for Cr(VI), and 0–20 µmol L−1 (0.995) and 0.2 µmol L−1 for Se(IV), respectively. Concentration of Se(VI) was estimated from the difference in its concentration between total Se and Se(IV). The analytical procedure for the determination of total Se included a reduction of Se(VI) to Se(IV) with hydrochloric acid and potassium bromide. The linear range of the calibration curve and detection limit for Se(VI) was 0–20 µmol L−1 (correction coefficient: 0.990) and 0.3 µmol L−1, respectively. The proposed method was applied to the determinations of Cr(VI), Se(IV), and Se(VI) in a river water sample. Recoveries of Cr and Se species ranged between 98 and 104%, and the relative standard deviations were about 5% at 10 µmol L−1 levels of the species.

Effects of dietary selenium supplementation on tissue selenium distribution and glutathione peroxidase activity in Chinese Ring Necked Pheasants

The objective of this study was to determine the concentration of total selenium (Se) and the proportions of total Se comprised as selenomethionine (SeMet) and selenocysteine (SeCys) in the postmortem tissues of female pheasants (Phasianus Colchicus Torquator) offered diets that contained graded additions of selenised-enriched yeast (SY) or a single comparative dose of sodium selenite (SS). Thiobarbituric acid reactive substances (TBARS) and tissue glutathione peroxidase (GSH-Px) activity of breast (Pectoralis Major) were assessed at 0 and 5 days postmortem. A total of 216 female pheasant chicks were enrolled into the study. Twenty-four birds were euthanased at the start of the study, and samples of blood, breast muscle, leg muscle (M. Peroneus Longus and M. Gastrocnemius), heart, liver, kidney and gizzard were collected for determination of total Se. Remaining birds were blocked by live weight and randomly allocated to one of four dietary treatments (n = 48 birds/treatment) that either differed in Se source (SY v. SS) or dose (control (0.17 mg total Se/kg), SY-L and SS-L (0.3 mg/kg total Se as SY and SS, respectively) and SY-H (0.45 mg total Se/kg)). Following 42 and 91 days of treatment, 24 birds per treatment were euthanased, and samples of blood, breast muscle, leg muscle, heart, liver, kidney and gizzard were retained for determination of total Se and the proportion of total Se comprised as SeMet or SeCys. Whole blood GSH-Px activity was determined at each time point. Tissue GSH-Px activity and TBARS were determined in breast tissue at the end of the study. There were increases in both blood and tissues to the graded addition of SY to the diet (P < 0.001), but the same responses were not apparent with the blood and tissues of selenite-supplemented birds receiving a comparable dose (SY-L v. SS-L). Although there were differences between tissue types in the distribution of SeMet and SeCys, there were few differences between treatments. There were effects of treatment on erythrocyte GSH-Px activity (P = 0.012) with values being higher in treatments SY-H and SS-L when compared with the negative control and treatment SY-L. There were no effects of treatment on tissue GSH-Px activity, which is reflected in the overall lack of any treatment effects on TBARS.

Selenium speciation in paired serum and cerebrospinal fluid samples

Se speciation was performed in 24 individual paired serum and cerebrospinal fluid (CSF) samples from neurologically healthy persons. Strong anion exchange (SAX) separation, coupled to inductively coupled plasma-dynamic reaction cell-mass spectrometry (ICP-DRC-MS), was employed. Species identification was done by standard matched retention time, standard addition and by size exclusion chromatography followed from SAX (2-D SEC-SAX-ICP-DRC-MS) and by SAX followed from CE-ICP-DRC-MS (2-D SAX-CE-ICP-DRC-MS). Limit of detection (LoD, 3×standard deviation (SD) of noise) was in the range of 0.026-0.031 μg/L for all investigated species and thus was set uniformly to 0.032 μg/L. Quality control for total Se determination was performed by analysing control materials "human serum" and "urine", where determined values met target values. Several Se species were found in both sample types having following median values (sequence: serum/CSF, each in μg Se/L): total Se, 58.39/0.86; selenoprotein P (SePP), 5.19/0.47; Se-methionine (SeM), 0.23/<LoD; glutathione peroxidase (GPx), 4.2/0.036; thioredoxinreductase (TrxR), 1.64/0.035; Se IV, 12.25/0.046; Se-human serum albumin (Se-HSA), 18.03/0.068. Other Se species, such as Se-cystine (SeC), Se VI and up to four non-identified compounds were monitored (if ever) only in very few samples usually close to LoD. Therefore, their median values were <LoD. Linear relationships based on median values provide information about Se-species passage across neural barriers (NB): SePP(-serum) is significantly correlated to total Se(-serum) when the latter was > 65 μg/L; however, SePP(-CSF) appeared independent of SePP(-serum). For Se-HSA(-serum) versus (vs.) Se-HSA(-CSF), a weak linear relationship was found (r(2)=0.1722). On the contrary, for anti-oxidative Se-enzymes, higher r (2) values were calculated: GPx(-serum) vs. GPx(-CSF), r(2)=0.3837; TrxR(-serum) vs. TrxR(-CSF), r(2)=0.6293. Q(-Se-species) values (= ratios of CSF(-Se-species)/serum(-Se-species)) were compared with the Q (-Alb) value (HSA(-CSF)/HSA(-serum)=clinical index of NB integrity) for deeper information about NB passage of Se species. The Q (-Se-HSA) value (3.8×10(-3)) was in accordance to the molecular mass dependent restriction at NB (Q(-Alb) at 5.25×10(-3)). Increased Q values were seen for TrxR (21.3×10(-3)) and GPx (8.3×10(-3)) which are not (completely) explained by molecular size. For these two anti-oxidative Se-enzymes (GPx, TrxR), we hypothesize that there might be either a facilitated diffusion across NB or they might be additionally synthesized in the brain.

Determination of Se using a solid-phase micro-extraction device coupled to a graphite furnace and detection by gas chromatography-mass spectrometry

A solid-phase micro-extraction (SPME) method using an SPME fiber device and graphite furnace (GF) for extracting Se compounds was proposed. Various factors affecting the derivatization and extraction of Se(IV) by SPME-GF were evaluated, including the effect of acid (type and concentration), the concentration of the derivatizing agent, the derivatization temperature, the extraction and derivatization times and the extraction temperature. After optimizing these conditions, the quantification of Se(IV) was performed by Gas Chromatography-Mass Spectrometry (GC-MS). The limit of detection was 0.37 μg L(-1) for Se(IV). The method was successfully applied to the total Se determination in certified reference materials (BCR-414 and SRM 1643e). A recovery of 97% was obtained for water (SRM 1643e). After microwave oven decomposition and the reduction of selenium using a mixture of 2 mol L(-1) HCl and 1% (w/v) KBr, a recovery of 101% and a relative standard deviation of 3.5% were attained for plankton (BCR-414). The SPME-GF method combined with GC-MS was also applied to the determination of the total selenium in a drug sample (selenium chelate).

Effect of dietary supplementation with selenium-enriched yeast or sodium selenite on selenium tissue distribution and meat quality in commercial-line turkeys

The objective of this study was to determine the concentration of total selenium (Se) and proportions of total Se comprised as selenomethionine (SeMet) and selenocysteine (SeCys) in the tissues of female turkeys offered diets containing graded additions of selenized-enriched yeast (SY), or sodium selenite (SS). Oxidative stability and tissue glutathione peroxidase (GSH-Px) activity of breast and thigh muscle were assessed at 0 and 10 days post mortem. A total of 216 female turkey poults were enrolled in the study. A total of 24 birds were euthanized at the start of the study and samples of blood, breast, thigh, heart, liver, kidney and gizzard were collected for determination of total Se. Remaining birds were blocked by live weight and randomly allocated to one of four dietary treatments (n = 48 birds/treatment) that differed either in Se source (SY v. SS) or dose (Con [0.2 mg/kg total Se], SY-L and SS-L [0.3 mg/kg total Se as SY and SS, respectively] and SY-H [0.45 mg total Se/kg]). Following 42 and 84 days of treatment 24 birds per treatment were euthanized and samples of blood, breast, thigh, heart, liver, kidney and gizzard were retained for determination of total Se and the proportion of total Se comprised as SeMet or SeCys. Whole blood GSH-Px activity was determined at each time point. Tissue GSH-Px activity and thiobarbituric acid reactive substances were determined in breast and thigh tissue at the end of the study. There were responses (P < 0.001) in all tissues to the graded addition of dietary Se, although rates of accumulation were highest in birds offered SY. There were notable differences between tissue types and treatments in the distribution of SeMet and SeCys, and the activity of tissue and erythrocyte GSH-Px (P < 0.05). SeCys was the predominant form of Se in visceral tissue and SeMet the predominant form in breast tissue. SeCys contents were greater in thigh when compared with breast tissue. Muscle tissue GSH-Px activities mirrored SeCys contents. Despite treatment differences in tissue GSH-Px activity, there were no effects of treatment on any meat quality parameter.

Ultrasonic assisted enzymatic digestion (USAED) coupled with high performance liquid chromatography and electrothermal atomic absorption spectrometry as a powerful tool for total selenium and selenium species control in Se-enriched food supplements

Abstract The suitability of hyphenated USAED with HPLC separation and ET-AAS determination as a new rapid methodology for Se control in Se-enriched food supplements is demonstrated. Total Se determination and Se speciation are accomplished in a single sample treatment using low sample amounts (ca. 10 mg), and low extracting volume (1 mL). The total Se content in seven of the 10 Se-enriched supplements studied was in agreement with the values obtained after microwave pressurized acid digestion, MW, (test t , p = 0.05) . The Se species studied were Se(IV), Se(VI), SeMet, SeMeSeCys, and SeCys 2 , being some of the most common found in the 10 supplements studied. Although SeMet was the Se species expected to be present at the highest concentration in most Se-enriched food supplements, we detected it in only three of the 10 samples studied. In the other seven samples, two of them had Se(IV) as the main Se species. The other five supplements had Se species that did not match with any of the five standards selected by us. We have also systematically demonstrated that ultrasonication does not alter the following Se species: Se(IV), Se(VI), SeMet, SeMeSeCys, and SeCys 2 . The new procedure can be easily adapted to more Se species and can be routinely used for Se control in Se-enriched food supplements. Concerning the supplements studied, our results suggest that stricter control on the Se content in enriched food supplements in terms of Se species will need to become mandatory.

Certification of a new selenized yeast reference material (SELM-1) for methionine, selenomethinone and total selenium content and its use in an intercomparison exercise for quantifying these analytes

A new selenized yeast reference material (SELM-1) produced by the Institute for National Measurement Standards, National Research Council of Canada (INMS, NRC) certified for total selenium (2,059+/-64 mg kg(-1)), methionine (Met, 5,758+/-277 mg kg(-1)) and selenomethionine (SeMet, 3,431+/-157 mg kg(-1)) content is described. The +/-value represents an expanded uncertainty with a coverage factor of 2. SeMet and Met amount contents were established following a methanesulfonic acid digestion of the yeast using GC-MS and LC-MS quantitation. Isotope dilution (ID) calibration was used for both compounds, using 13C-labelled SeMet and Met. Total Se was determined after complete microwave acid digestion based on ID ICP-MS using a 82Se spike or ICP-OES spectrometry using external calibration. An international intercomparison exercise was piloted by NRC to assess the state-of-the-art of measurement of selenomethione in SELM-1. Determination of total Se and methionine was also attempted. Seven laboratories submitted results (2 National Metrology Institutes (NMIs) and 5 university/government laboratories). For SeMet, ten independent mean values were generated. Various acid digestion and enzymatic procedures followed by LC ICP-MS, LC AFS or GC-MS quantitation were used. Four values were based on species-specific ID calibration, one on non-species-specific ID with the remainder using standard addition (SA) or external calibration (EC). For total selenium, laboratories employed various acid digestion procedures followed by ICP-MS, AFS or GC-MS quantitation. Four laboratories employed ID calibration, the remaining used SA or EC. A total of seven independent results were submitted. Results for methionine were reported by only three laboratories, all of which used various acid digestion protocols combined with determination by GC-MS and LC UV. The majority of participants submitted values within the certified range for SeMet and total Se, whereas the intercomparison was judged unsuccessful for Met because only two external laboratories provided values, both of which were outside the certified range.

Hollow fiber liquid phase microextraction combined with electrothermal vaporization ICP-MS for the speciation of inorganic selenium in natural waters

A novel method for the speciation of Se(IV) and Se(VI) in environmental water samples based on liquid-phase microextraction (LPME) methods in conjunction with electrothermal vaporization (ETV) ICP-MS has been developed. Two modes of LPME: single drop microextraction (SDME) and hollow fiber liquid phase microextraction (HF-LPME) were studied comparatively. The organic chelating reagent ammonium pyrrolidine dithiocarbamate (APDC) was used as both the extractant for microextraction and the chemical modifier for ETV-ICP-MS determination. Under the optimal conditions, enrichment factors of 75 and 410 could be achieved for SDME and HF-LPME, respectively. The detection limit of Se in HF-LPME-ETV-ICP-MS and SDME-ETV-ICP-MS were 0.50, 0.56 pg mL−1 and 2.7, 3.0 pg mL−1 for Se(IV) and Se(VI), respectively. HF-LPME was finally selected for the analysis of Se(IV) and Se(VI) in lake water, river water and pool water samples due to its good analytical features and robustness. The proposed method was validated by the determination of total Se with PN-ICP-MS.

The determination of total Se in urine and serum by graphite furnace atomic absorption spectrometry using Ir as permanent modifier and in situ oxidation for complete trimethylselenonium recovery

The present work evaluated the use of iridium (Ir) as permanent modifier for the determination of total selenium in urine and serum by graphite furnace atomic absorption spectrometry. Concerning urine, the presence of trimethylselenonium (TMSe(+)) was especially considered. Pyrolysis and atomization temperatures of 1,000 and 2,100 degrees C, respectively, were used. For nondigested urine and serum samples, 0.2% v/v HNO(3) and Triton X-100 were used as diluents, respectively, and the same initial platform Ir treatment was effective for up to 1,100 atomization cycles. Good precision [less than 5% relative standard deviation (RSD)] can be achieved with the proposed method. Low TMSe(+) recovery was observed for nondigested urine samples. Thus, if this species is to be considered in urine analysis, a previous external mineralization step was found to be necessary. Alternatively, an in situ oxidation treatment was developed. Detection limits of 8, 10, and 7 mug l(-1) were obtained after dilution, microwave-assisted digestion, and in situ oxidation procedures, respectively. The accuracy of the method was validated by the analysis of certified reference or commercial quality control materials and spiked samples.

Evaluation of different sample extraction strategies for selenium determination in selenium-enriched plants ( Alliumsativum and Brassicajuncea) and Se speciation by HPLC-ICP-MS

Several sample extraction techniques have been evaluated in order to obtain highest selenium (Se) extraction efficiency in two types of selenium-enriched plants ( Allium sativum and Brassica juncea). Three extracting solutions have been studied for this purpose: 0.1 M HCl, 25 mM ammonium acetate buffer (pH 5.6) and protease in aqueous solution. In each case, the effect of the ultrasonic probe during extraction was also evaluated. Selenium extraction yields were calculated based on the ICP-MS determination of the total selenium content in the corresponding extracts and in the plant tissue after its microwave digestion. The action of ultrasounds allowed the reduction on the extraction time while maintaining good Se recoveries (which ranged from 75 to 120% of the total Se in the plant). The accuracy of total Se determination was controlled by analyzing a reference material (aquatic plant, BCR-670). On the other hand, speciation studies of the extracts were carried out by using ion-pairing reversed phase and size exclusion/ion exchange (Shodex Asshipak) liquid chromatographic columns. The two separation mechanisms were suitable to isolate the main extractable Se species which were identified as Se-methyl selenocysteine and Se-methionine in both systems. The extracts of both plants ( A. Sativum and B. juncea) exhibited also the presence of several unknown Se-species.

Hydride generation-headspace single-drop microextraction-electrothermal atomic absorption spectrometry method for determination of selenium in waters after photoassisted prereduction

A headspace single-drop microextraction (SDME) method has been developed in combination with electrothermal atomic absorption spectrometry for determination of total inorganic Se and Se(IV). SeH 2 is generated in a 40 mL volume closed-vial and trapped onto a Pd(II)-aqueous containing drop that is supported at the needle tip of a high-precision chromatographic syringe. Sample pre-treatment by UV irradiation prior to hydride generation allowed converting Se(VI) into Se(IV), hence, facilitating total Se determination. A 2 IV 6-2 fractional factorial design was employed for characterising the effect of relevant variables over SeH 2 trapping. The variables showing the most significant effect were Pd(II) concentration in the drop and extraction time. A preconcentration factor of about 25 is achieved. The limit of detection of Se was 0.15 ng/mL using trapping onto a 3-μL drop and the precision expressed as relative standard deviation was about 3%. The limit of detection could be improved further using repeated sampling of the headspace.

Preparative liquid isoelectric focusing (Rotofor IEF) based Se-speciation of Se-enriched Agaricus bisporus

Preparative isoelectric focusing (Rotofor) was introduced to carry out the prefractionation of a selenised edible mushroom Agaricus bisporus sample containing 1037 ± 31 (SD) μg Se g−1. The water-soluble part of the sample was separated by the free solution apparatus into 20 fractions on the base of the pI values of the sample components. The separation was followed by the determination of total Se, soluble protein (by Bradford method) and Se-speciation of the fractions, summed up in 14 pools according to the actual individual pH values. Proteolytic sample preparation was chosen prior to the speciation analysis carried out with the help of a HPLC-UV-HG-AFS system, applying cation and anion exchange chromatographies. Achieving 19% column recovery, the presence of Se(IV), selenomethionine, selenocystine and methylselenocysteine was detected, the latter for the first time in a mushroom sample.

Enzymatic probe sonication: enhancement of protease-catalyzed hydrolysis of selenium bound to proteins in yeast.

This paper describes the dramatic activity enhancement of two proteolytic enzymes (protease XIV and subtilisin) when treated with an ultrasonic probe and their application to total Se determination and Se speciation in biological samples. Total Se extraction from enriched yeast is performed with 10 mg of yeast plus 1 mg of protease with a sonication time of 5 s, whereas 30 s is needed for extracting selenomethionine. In both cases, aqueous media was used. This spectacular finding is important because the enzymatic procedure usually requires a long treatment period at 37 degrees C. In addition to this major advantage, no control temperature is needed and the risk of species interconversion is drastically reduced or inhibited (the same Se species were detected after different sonication times). Moreover, the extraction is performed in water, minimizing contamination risk and without further pH adjustment. The new sample treatment proposed has been successfully applied to selenium speciation in yeast using chromatographic separation (HPLC) coupled to inductively coupled plasma-mass spectrometry.

Total determination and quantitative speciation analysis of selenium in yeast and wheat flour by isotope dilution analysis ICP-MS

Isotope dilution analysis (IDA) has been used to carry out the determination of total Se as well as Se speciation analysis in samples of yeast and wheat flour using an ICP-(Q)MS with an octapole reaction system (ORS). Total selenium was determined after microwave digestion of the samples, whereas enzymatic hydrolysis with protease and lipase was used for the speciation studies. Speciation analysis was performed by using an anion exchange column in order to separate the Se compounds. The separated Se species, eluting from the column, were quantified on-line by post-column IDA using an enriched 77Se spike solution, after adequate conversion of intensity chromatograms into mass flow chromatograms. To do this, the 78Se/77Se ratio was monitored, avoiding the 38Ar40Ar polyatomic interference on the 78Se isotope by pressurizing the octapole chamber with hydrogen. Under such conditions significant formation of SeH+ ions occurred which had to be mathematically corrected. Results showed that the main seleno-compound found in both matrices was selenomethionine, with concentration levels of approximately 59% of total Se for wheat flour and of 68% for yeast. Se(IV) and Se(VI) were detected in yeast samples, but only Se(IV) was present at a level to be quantified. Conversely, those two inorganic species of Se were not detected in wheat flour. The obtained results were included in an inter-laboratory exercise, organised by the University of Plymouth Enterprise Ltd. (UK), with excellent agreement between our results and the average obtained from the rest of the participants.

Alkaline fusion-alkaline mode HG-ICP spectrometry for selenium determination

A fully alkaline procedure, including alkaline fusion, pre-reduction of Se(VI) to Se(IV) in alkaline medium and an alkaline mode of H2Se generation, together with ICP-AES for the determination of total Se in biological and environmental samples, is described. Alkaline fusion coupled with alkaline mode hydride generation could effectively avoid volatile losses of selenium by changing it into soluble salts such as selenate or selenite and greatly eliminate the chemical interference from the co-existing transition metals Fe, Cu, and Mn. The method was verified with a certified reference material and was successfully applied to several real samples such as selenium-enriched plasma, egg, animal feeds and soils with satisfactory results.

Problems of selenium fractionation in soils rich in organic matter

Hydride generation atomic absorption spectrometry (HGAAS) was used for the determination of Se in soils. Potential interferences from metal ions and spectral interference in the heated quartz tube were documented and eliminated. The efficiency of four acid-based closed vessel decomposition procedures was checked with certified reference soils and a pressured microwave sample preparation using (1 + 1) HNO 3 : H 2SO 4 was recommended for the determination of total Se components in soils. The effect of a high content of organic matter on the reliable determination of Se was examined and eliminated. A sequential extraction procedure was developed for the determination of the speciation of Se in a forest soil profile. The detection limit for the total Se determination was 6 ng Se/g soil, and the relative standard deviations were <5% after application of the sequential extraction procedure. The proposed method was applied to a real forest soil sample and the vertical distribution of Se species in the soil profile was investigated and evaluated.