Yolanda Madrid

Novel approaches for selenium speciation in foodstuffs and biological specimens: a review.

Selenium is an essential element for human health. It has been recognized as an antioxidant and chemopreventive agent in cancer. Selenium is known to develop its biological activity via selenocysteine residue in the catalytically active centre of selenoproteins. The main source of selenium in human beings is the diet. However, in several regions of the world the content of selenium in diet has been estimated insufficient for a correct expression of the proteins. The beneficial effects of selenium on human health are strongly dependent on its chemical form and concentration. This review critically evaluated the state-of-the art of selenium speciation in biological matrices mainly focused in nutritional and food products. Besides the number of publications related to selenium speciation, isolation and accurate characterization and quantification of selenium species is still a challenge. Hyphenated techniques based on coupling chromatography separation with inductively coupled plasma spectrometry (ICP-MS) and its combination with molecular mass spectrometry (ESI-MS, ESI-MS-MS and MALDI-TOF) and isotopic dilution allow identification, quantification and structural characterization of selenium species. Particular attention is paid in the development of Se-enriched food and nutritional products and how the application of the techniques mentioned above is mandatory to get reliable results on selenium metabolisms in these particular matrices.

Biological substrates for metal preconcentration and speciation

Abstract This article summarizes the state of the art of metal preconcentration and speciation using biological organisms such as algae, plant-derived materials, bacteria, yeast, fungi and erythrocytes. Although biosorption has been the subject of increasing research for a variety of reasons, including its potential application in the recovery of metals from manufacturing processes, the treatment of contaminated water and the recovery of precious metals in mining operations, only recently has it been exploited for analytical measurement. Basic techniques and principles are discussed and recent developments reviewed. Special attention is given to immobilization procedures and some biosorption mechanisms are considered.

Evaluation of selective uptake of selenium (Se(IV) and Se(VI)) and antimony (Sb(III) and Sb(V)) species by baker's yeast cells (Saccharomyces cerevisiae)

Abstract Common bakers yeast cells characterized as Saccharomyces cerevisiae were evaluated as a means of sequestering Se and Sb in different oxidation states (Se(IV), Se(VI), Sb(III) and Sb(V)) from aqueous solution. Several parameters affecting the degree of bioaccumulation of these elements were studied — solution pH, temperature, incubation time, and amount of biomass and analyte. The results obtained show that the biosorption process and its mechanism depend not only on the element but also on its oxidation state. In presence of yeast, aqueous Se(VI) remained unaltered and in solution under all the experimental conditions tested while Se(IV) is accumulated into the cell. The degree of accumulation depends on the amount of yeast, incubation time and temperature. Se(IV) is quantitatively bound to the yeast under the optimum conditions, i.e. 700 mg bakers yeast, 30 min incubation time at pH 7.0 and 37 °C. The accumulation step may occur along with transformation processes of Se(IV), probably a reduction to Se(-II) species. Sb(III) was completely bound to the yeast cells at an incubation temperature of 60°C at pH 7, whereas Sb(V) showed less affinity and was unaffected under these conditions. The proposed method allows the specific sampling of Se and Sb species, which is especially important in environmental analysis since Sb(III) and Se(IV) are more toxic than Sb(V) and Se(VI), respectively.

Separation and determination of antimony(III) and antimony(V) species by high-performance liquid chromatography with hydride generation atomic absorption spectrometric and inductively coupled plasma mass spectrometric detection

Methods are described for the effective separation and determination of inorganic antimony species by high-performance liquid chromatography (HPLC)–hydride generation (HG) atomic absorption spectrometry (AAS), HPLC–inductively coupled plasma (ICP) mass spectrometry (MS) and HPLC–HG–ICP-MS. SbIII and SbV were separated on a strong anion-exchange column using phthalic acid as the mobile phase. The optimum conditions for the separation of the antimony species by HPLC and the hydride generation conditions for the determination by AAS were established. Then, the HPLC system was connected to an ICP-MS system using either nebulization or hydride generation sample introduction to improve the detection limits. The detection limits were 5 and 0.6 ng per 100 µl sample for SbIII and SbV, respectively (HPLC–HGAAS). For the HPLC–ICP-MS determination these limits were 0.75 and 0.09 ng and 0.04 and 0.008 ng for the HPLC–HG-ICP-MS coupling. The proposed methods for the simultaneous separation of inorganic antimony species were applied to the determination of SbIII and SbV in spiked and natural water samples. Agreement within the statistical uncertainty was obtained in all instances.

Quantification and speciation of mercury and selenium in fish samples of high consumption in Spain and Portugal.

Mercury (Hg) and selenium (Se) determinations were carried out to evaluate human exposure to those elements through fish consumption in Spain and Portugal. Atomic fluorescence spectroscopy (AFS) was applied in a cold vapor mode for total mercury quantification and was also hyphenated to gas chromatography (GC) to achieve the speciation of organomercurial species in fish samples. The results obtained show the highest concentration of Hg in swordfish and tuna (0.47±0.02 and 0.31±0.01 μg g−1, respectively), and a much lower concentration in sardine, mackerel shad, and octopus (0.048±0.002, 0.033±0.001, and 0.024±0.001 μg g−1, respectively), The determination of alkyl mercury compounds revealed that 93–98% of mercury in the fish samples was in the organic form. Methylmercury (MeHg) was the only species found in the three fish species with higher mercury content.Total selenium concentraton was high in sardine, swordfish, and tuna (0.43±0.02, 0.47±0.02, and 0.92±0.01 μg g−1, respectively), but low in mackeral shad and octopus (0.26±0.01 and 0.13±0.01 μg g−1, respectively). Speciation of selenium compounds was done by high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry (LC-ICP-MS). Selenomethionine (SeMet) was the only selenium compound identified in the fish samples with higher selenium content.Among the fish species studied, sardine had the most favourable Se:Hg and SeMet:MeHg molar ratios; therefore, its consumption seems to be preferable.

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.

Prospects and difficulties in TiO2 nanoparticles analysis in cosmetic and food products using asymmetrical flow field-flow fractionation hyphenated to inductively coupled plasma mass spectrometry

In this work, we proposed an analytical approach based on asymmetrical flow field-flow fractionation combined to an inductively coupled plasma mass spectrometry (AsFlFFF-ICP-MS) for rutile titanium dioxide nanoparticles (TiO2NPs) characterization and quantification in cosmetic and food products. AsFlFFF-ICP-MS separation of TiO2NPs was performed using 0.2% (w/v) SDS, 6% (v/v) methanol at pH 8.7 as the carrier solution. Two problems were addressed during TiO2NPs analysis by AsFlFFF-ICP-MS: size distribution determination and element quantification of the NPs. Two approaches were used for size determination: size calibration using polystyrene latex standards of known sizes and transmission electron microscopy (TEM). A method based on focused sonication for preparing NPs dispersions followed by an on-line external calibration strategy based on AsFlFFF-ICP-MS, using rutile TiO2NPs as standards is presented here for the first time. The developed method suppressed non-specific interactions between NPs and membrane, and overcame possible erroneous results obtained when quantification is performed by using ionic Ti solutions. The applicability of the quantification method was tested on cosmetic products (moisturizing cream). Regarding validation, at the 95% confidence level, no significant differences were detected between titanium concentrations in the moisturizing cream prior sample mineralization (3865±139 mg Ti/kg sample), by FIA-ICP-MS analysis prior NPs extraction (3770±24 mg Ti/kg sample), and after using the optimized on-line calibration approach (3699±145 mg Ti/kg sample). Besides the high Ti content found in the studied food products (sugar glass and coffee cream), TiO2NPs were not detected.

Advanced oxidation processes for sample treatment in atomic spectrometry

Abstract Advanced oxidation processes (AOPs), which involve the in situ generation of highly potent chemical oxidants, such as the hydroxyl radical ( OH ), have emerged as an important class of sample treatments in atomic spectrometry. This article introduces the state-of-the-art of the main AOPs used in analytical chemistry along with an in-depth review of the most representative works published for each of the AOPs selected and some guidelines regarding their near-term future.

Speciation of antimony by atomic absorption spectrometry. Applicability to selective determination of Sb(III) and Sb(V) in liquid samples and of bioavailable antimony in sediments and soil samples

A comparative study was made of several methods to speciale Sb(III) and Sb(V) by AAS: 1) Selective extraction of Sb(III) with lactic acid/malachite green graphite furnace-AAS, 2) Sb(III) and total antimony determination by hydride generation-AAS coupled to flow injection, batch, and continuous flow systems. These methods were applied to determine total antimony and Sb(III) in sea and surface water and total antimony in sediments and in soil. For soils different sample pretreatments were used: HNO3-H2SO4-HC1O4, HF-HNO3-H2SO4-HC1O4, cold aqua regia and slurry formation procedures in water and 4M HC1. In each case the recovery of total antimony and the ability to selective determine Sb(III) were studied. The detection limits obtained were 0.01 ng, 0.07 ng, 2.97 ng and 0.21 ppb for GF-AAS, FIA-HG-AAS, HG (Batch)-AAS, and HG (continuous flow)-AAS, respectively.

Evaluation of atomic fluorescence and atomic absorption spectrometric techniques for the determination of arsenic in wine and beer by direct hydride generation sample introduction

A simple and rapid flow injection-arsenic hydride generation-atomic fluorescence spectrometric (FI-HG-AFS) method has been optimized for the direct determination of arsenic in untreated samples of beer and wine. Several aspects were evaluated: concentration of HCl and NaBH 4 , argon and hydrogen flow-rates and effect of oxidation state on the analytical signal. The optimum conditions selected were 6 m HCl and 0.5% (m/v) NaBH 4 and 6 m HCl and 1% (m/v) NaBH 4 to determine total arsenic contents of different brands of beer and wine, respectively. The accuracy of the method was evaluated by comparing the results obtained with those provided for three mineralization procedures: HNO 3 -H 2 O 2 , H 2 SO 4 -HNO 3 -HClO 4 and Mg(NO 3 ) 2 -MgO mixtures. The results obtained showed good agreement between the conventional digestion procedures and the direct determination of arsenic in the untreated samples. The method enables the determination of arsenic to be made in untreated samples with detection limits of 0.3 and 0.5 µg L –1 for beer and wine, respectively.