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 speciatedcertified reference materials (CRMs) are to be produced for validation of measurements of target Se-containing species in Se-food supplements.     

Development and validation of a glass-silicon microdroplet-based system to measure sulfite concentrations in beverages

Sulfite is often added to beverages as an antioxidant and antimicrobial agent. In fermented beverages, sulfite is also naturally produced by yeast cells. However, sulfite causes adverse health effects in asthmatic patients and accurate measurement of the sulfite concentration is therefore very important. Current sulfite analysis methods are time- and reagent-consuming and often require costly equipment. Here, we present a system allowing sensitive, ultralow-volume sulfite measurements based on a reusable glass-silicon microdroplet platform on which microdroplet generation, addition of enzymes through chemical-induced emulsion destabilization and pillar-induced droplet merging, emulsion restabilization, droplet incubation, and fluorescence measurements are integrated. In a first step, we developed and verified a fluorescence-based enzymatic assay for sulfite by measuring its analytical performance (LOD, LOQ, the dynamic working range, and the influence of salts, colorant, and sugars) and comparing fluorescent microplate readouts of fermentation samples with standard colorimetric measurements using the 5,5′-dithiobis-(2-nitrobenzoic acid) assay of the standard Gallery Plus Beermaster analysis platform. Next, samples were analyzed on the microdroplet platform, which also showed good correlation with the standard colorimetric analysis. Although the presented platform does not allow stable reinjection of droplets due to the presence of a tight array of micropillars at the fluidics entrances to prevent channel clogging by dust, removing the pillars, and integrating miniaturized pumps and optics in a future design would allow to use this platform for high-throughput, automated, and portable screening of microbes, plant, or mammalian cells.

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A new thermoelectric material: CsBi4Te6

The highly anisotropic material CsBi(4)Te(6) was prepared by the reaction of Cs/Bi(2)Te(3) around 600 degrees C. The compound crystallizes in the monoclinic space group C2/m with a = 51.9205(8) A, b = 4.4025(1) A, c = 14.5118(3) A, beta = 101.480(1) degrees, V = 3250.75(11) A(3), and Z = 8. The final R values are R(1) = 0.0585 and wR(2) = 0.1127 for all data. The compound has a 2-D structure composed of NaCl-type [Bi(4)Te(6)] anionic layers and Cs(+) ions residing between the layers. The [Bi(4)Te(6)] layers are interconnected by Bi-Bi bonds at a distance of 3.2383(10) A. This material is a narrow gap semiconductor. Optimization studies on the thermoelectric properties with a variety of doping agents show that the electrical properties of CsBi(4)Te(6) can be tuned to yield an optimized thermoelectric material which is promising for low-temperature applications. SbI(3) doping resulted in p-type behavior and a maximum power factor of 51.5 microW/cm.K(2) at 184 K and the corresponding ZT of 0.82 at 225 K. The highest power factor of 59.8 microW/cm.K(2) at 151 K was obtained from 0.06% Sb-doped material. We report here the synthesis, physicochemical properties, doping characteristics, charge-transport properties, and thermal conductivity. Also presented are studies on n-type CsBi(4)Te(6) and comparisons to those of p-type.     

Determination of picogram amounts of lipoxin A4 and lipoxin B4 by high-performance liquid chromatography with electrochemical detection

A new method for the determination of lipoxins with electrochemical detection after high-performance liquid chromatography is described. The half-wave potentials of lipoxin A4 and lipoxin B4 at a glassy carbon electrode and a mobile phase of methanol-water (65:35 v/v) and 1 mM trifluoroacetic acid was found to be +1.14 V versus an Ag/AgCl reference electrode. The use of trifluoroacetic acid instead of sulphuric acid and lithium perchlorate led to a background current of 6-8 nA at +1.20 V. The detection limits for both lipoxins, based on a signal-to-noise ratio of 3:1 were found to be 5-10 pg (15-30 fmol). The new method was applied to an extract of human polymorphonuclear granulocytes, preincubated with 15-hydroxyeicosatetraenoic acid and stimulated with Ca2+ ionophore A23187.     

Neuere Entwicklungen der flammenphotometrischen Analysenverfahren

Zusammenfassung Es wird gezeigt, daß man durch Einsatz von reduzierenden Flammen, durch Einsatz von Chemiluminescenzvorgängen in Flammen, durch Atomabsorptionsverfahren, durch Modulations- und Differentiations-operationen eine Reihe von weiteren Elementen mit den schnellen und spezifischen Flammenmethoden analytisch gut erfassen kann. Hierbei wird insbesondere auf die Bestimmung von Spurenelementen in Mikroproben mit möglichst einfachen Mitteln eingegangen.

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Summary It is demonstrated that one can grasp analytically well a series of further elements with the quick and specific flame methods by use of chemiluminescence processes in flames, by atomic absorption methods, by operations of modulation and differentiation. Hereby the determination of trace elements is specifically treated in microprobes with the most possible simple means.

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Unterstützt mit Mitteln der Deutschen Forschungsgemeinschaft.

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Herrn Prof. Dr. Bohnstedt zum 65. Geburtstag gewidmet.

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Meinen Mitarbeitern, insbesondere Herrn Dipl. Phys. W. Lang und Frau B. Gutsche, die an den zuletzt besprochenen Ergebnissen einen maßgeblichen Anteil hatten, als auch der Deutschen Forschungsgemeinschaft sei an dieser Stelle herzlichst gedankt.     

Preparation and dilute solution properties of model gemini nonionic surfactants

Dimeric poly(ethylene oxide) surfactants (or nonionic gemini surfactants) with the structure (Cn-2H2n-3CHCH2O(CH2CH2O)mH)2(CH2)6 (or GemnEm), where n is the alkyl length and m is the average number of ethylene oxides per head group, were synthesized. Surfactants were synthesized with alkyl chain lengths n = 12, 14, and 20 and m = 5, 10, 15, 20, and 30. Water solubilities and cloud temperatures at 1 wt% were determined by measuring turbidity as a function of temperature. Cloud temperatures increase with m and decrease with n, as observed for conventional surfactants. For large m the cloud temperatures were all above 100 degrees C. Surfactants with small m (i.e., n = 12, 14, m = 5 and n = 20, m = 10) were insoluble at room temperature, forming two-phase mixtures. Critical micelle concentrations (CMCs) were measured using a pyrene fluorescence method and are all in the range of 10(-7) to 10(-6) M, with the lowest values from the surfactants with large n and small m. CMCs of mixtures with both anionic and nonionic conventional (monomeric) surfactants were well described by an ideal mixing model.     

Identification of iodoorganic compounds in kerosene from nuclear fuel reprocessing

In kerosene samples from nuclear fuel reprocessing, iodoalkanes with chain-lengths from C₄ to C₁₃ have been identified. The kerosene samples were purified by means of solid-phase extraction. By this method other fission products like¹²⁵Sb and¹⁰⁶Ru were quantitatively removed from the solution. The only remaining radioactive nuclide was thus¹²⁹I. The iodoorganic compounds in the kerosene from the solvent were enriched from 6000 Bq/L to 100 000 Bq/L¹²⁹I by vacuum distillation. Chromatographic separation by HPLC, fractionation, and -measurement of the fractions showed that at least one polar and one nonpolar iodoorganic compound were present. Derivatisation of the iodoorganic compounds with, 1,4-diazabicyclo-2,2,2-octane to quatermary ammonium salts and²⁵²Cf plasma desorption mass spectrometry of the products revealed that the main iodoorganic constituents in the kerosene were iodobutane as polar and iodododecane as nonpolar compound in approximately equal concentrations.