Determination of phosphorus in biological material using electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser

Phosphorus has been determined by electrothermal atomisation atomic absorption spectrometry with a molybdenum tube atomiser. The effects of interferents on the phosphorus signal have been investigated. Chemical interferences were eliminated by high-temperature pyrolysis. The detection limit for the molybdenum tube system was 2.3 ng (corresponding to 2.3 micrograms ml-1 when 1 microliter was injected into the atomiser) and the characteristic mass was 1.9 ng of phosphorus. A calibration graph method combined with high-temperature pyrolysis has been evaluated through the determination of phosphorus in biological materials. The sensitivity, accuracy and precision of the method were superior to or nearly equal to those of graphite furnace atomic absorption spectrometry. The advantages of the high-temperature pyrolysis method are its simplicity and low cost.     

Significant differences in site of protonation and extent of fragmentations in chemical ionization and fast atom bombardment mass spectrometry of simple bifunctional compounds. A mechanistic implication for formation of protonated molecules

Chemical ionization (CI) and fast atom bombardment (FAB) mass spectra of simple bifunctional aromatic compounds were compared. Some significant differences were revealed with respect to the site of protonation and extent of fragmentations. Unlike conventional CI ionization, the protonated molecule formation by FAB could not be accounted for by ordinary proton transfer reactions in the gas phase. The observed ions under FAB conditions appear to be regulated by proton exchange reactions through frequent collisions in some particular region between the matrix and the gas phase.     

Structural studies of the carbon monoxide complex of [NiFe]hydrogenase from Desulfovibrio vulgaris Miyazaki F: suggestion for the initial activation site for dihydrogen

The carbon monoxide complex of [NiFe]hydrogenase from Desulfovibrio vulgaris Miyazaki F has been characterized by X-ray crystallography and absorption and resonance Raman spectroscopy. Nine crystal structures of the [NiFe]hydrogenase in the CO-bound and CO-liberated forms were determined at 1.2-1.4 A resolution. The exogenously added CO was assigned to be bound to the Ni atom at the Ni-Fe active site. The CO was not replaced with H(2) in the dark at 100 K, but was liberated by illumination with a strong white light. The Ni-C distances and Ni-C-O angles were about 1.77 A and 160 degrees, respectively, except for one case (1.72 A and 135 degrees ), in which an additional electron density peak between the CO and Sgamma(Cys546) was recognized. Distinct changes were observed in the electron density distribution of the Ni and Sgamma(Cys546) atoms between the CO-bound and CO-liberated structures for all the crystals tested. The novel structural features found near the Ni and Sgamma(Cys546) atoms suggest that these two atoms at the Ni-Fe active site play a role during the initial H(2)-binding process. Anaerobic addition of CO to dithionite-reduced [NiFe]hydrogenase led to a new absorption band at about 470 nm ( approximately 3000 M(-1)cm(-1)). Resonance Raman spectra (excitation at 476.5 nm) of the CO complex revealed CO-isotope-sensitive bands at 375/393 and 430 cm(-1) (368 and 413 cm(-1) for (13)C(18)O). The frequencies and relative intensities of the CO-related Raman bands indicated that the exogenous CO is bound to the Ni atom with a bent Ni-C-O structure in solution, in agreement with the refined structure determined by X-ray crystallography.     

On the space curves with the same image under the gauss maps

From an irreducible complete immersed curveX in a projective space ? other than a line, one obtains a curveX ^′ in a Graasmann manifoldG of lines in ? that is the image ofX under the Gauss map, which is defined by the embedded tangents ofX. The main result of this article clarifies in case of positive characteristic what curvesX have the sameX′: It is shown thatX is uniquely determined byX′ ifX, or equivalentlyX′, has geometric genus at least two, and that for curvesX ₁ andX ₂ withX ₁ ≠X ₂ in ?, ifX′₁ =X′₂ inG and eitherX ₁ orX ₂ is reflexive, then bothX ₁ andX ₂ are rational or supersingular elliptic; moreover, examples of smoothX ₁ andX ₂ in that case are given.     

Distribution of the iron(III)-ethyl acetoacetate complex between aqueous solution and benzene

Summary Studies have been made on the distribution of iron(III)-ethyl acetoacetate complex between aqueous solution and benzene. Effect of pH, concentration of ethyl acetoacetate and shaking conditions were chosen as experimental parameters. Iron(III) can be well extracted from aqueous solution of pH 4.4–9.8 into benzene with constant extractability (97%), if the concentration of ethyl acetoacetate is kept in excess over that of iron(III). The applicability of the complex ( _max: 452 nm) to the spectrophotometric determination of iron is also discussed.

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Verteilung des Eisen(III)-Acetessigester-Komplexes zwischen wä\riger Lösung und Benzol

Zusammenfassung Zur Untersuchung der Verteilung wurden der pH-Wert, die Konzentration an Acetessigester und die Ausschüttelungsbedingungen variiert. Eisen(III) kann bei pH 4.4–9.8 mit Benzol mit einer konstanten Extrahierbarkeit von 97% ausgeschüttelt werden, wenn die Konzentration an Acetessigester größer ist als die an Eisen(III). Die Anwendbarkeit des Komplexes ( _max: 452 nm) zur spektralphotometrischen Eisenbestimmung wird diskutiert.

     

Determination of a polymeric hindered amine light stabilizer in polypropylene formulated with magnesium hydroxide flame retardant by reactive thermal desorption-gas chromatography.

A polymeric hindered amine light stabilizer (HALS), Tinuvin 622 (MW [symbol: see text] 4000), in PP materials formulated with a magnesium hydroxide flame retardant was determined by reactive thermal desorption (RTD) gas chromatography (GC). Two kinds of the HALS components that were formed through the RTD in the presence of tetramethylammonium hydroxide [(CH3)4NOH, TMAH] were clearly observed in the chromatograms of the PP samples, with negligible interference from the other additives and the PP substrate. Here, the coexisting flame retardant was proved to affect significantly the RTD process of the occluded HALS. As a result, the recovery of the HALS components in the RTD-GC chromatograms of the PP samples increased with increase in the content of the flame retardant. This enhancement of the HALS recovery is attributed mainly to the preferential exposure of the HALS on the surface of the ground PP sample through the interaction between the polymeric HALS and the flame retardant in the molten PP during kneading. In spite of such a considerable action of the flame retardant, the observed intensities of the characteristic peaks of HALS by RTD-GC showed a good linear relationship with the HALS content in the PP samples with constant content of the flame retardant (50 phr); this relationship could be used as the calibration line for the determination of the polymeric HALS in the PP materials containing the flame retardant.     

Volumetric study on the inclusion complex formation of α- and β-cyclodextrin with 1-alkanols at different temperatures

The partial molar volumes (V_a) of 1-alkanols (carbon number, m=5, 6, 7) in - and -cyclodextrin (CD) solutions at 5.00 mmol kg^–1 have been determined as a function of alkanol concentration (C_a) between 293.2 and 308.2 K by using a dilatometer. It has been observed that with an increase in C_a, V_a increased in -CD solution but decreased in -CD solution, asymptotically to a value of V_a in CD-free water. The dependence of V_a on C_a provided the binding constant (K) of 1:1 complex, the volume change in complex formation, and the partial molar volume of complex itself. The complex formation mechanism has been discussed on the basis of these values and their carbon number dependences in the respect of geometric behavior, hydrophobic interaction, and van der Waals interaction. It is concluded that the CD cavity in water is not rigid but flexible for fitting in nicely with guest molecule.     

Determination of cadmium in river water by sequential metal vapor elution analysis

Determination of cadmium in river water by sequential metal vapour elution analysis (column temperature; > 1500 K) with argon and hydrogen carrier gas and with atomic absorption spectrometric detection is described. The column is made of a molybdenum capillary tube (i.d. 1.22 mm) and the temperature is 1760 K. The cadmium vapor was separated from those of calcium, iron and sodium. The calibration graph was linear up to 15 μ/ml. Relative standard deviations of 0.8–4.3% were obtained in the range 1 to 15 μ/ml. Cadmium in spiked samples (river water) was determined. The results were in good agreement with the amount spiked.     

Facile S-alkyl thiocarbamate synthesis by a novel DBU-assisted carbonylation of amines with carbon monoxide and sulfur

A novel DBU-assisted carbonylation of amines with carbon monoxide and sulfur has been developed for the synthesis of S-alkyl thiocarbamates. In the presence of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), S-alkyl thiocarbamates are synthesized in excellent yields from amines, carbon monoxide, sulfur, and alkyl halides under mild conditions (1 atm, 20°C). In the absence of DBU, however, no formation of S-alkyl thiocarbamate is observed. The present DBU-assisted carbonylation can also be applied to new synthetic methods for benthiocarb and orthobencarb (herbicides) and carbamoyl chlorides.