Simultaneous determination of metal ion concentrations in binary mixtures with a multi-LED photometer

 A compact photometer is based on up to seven different light-emitting diodes whose light is guided into a photometric cell by means of a fibre-optic coupler. The wavelength is selected by switching on the appropriate light source. The application of this multi-wavelength photometer to the determination of binary metal ion samples is demonstrated using model mixtures. Solutions of Fe, Co, Cu, Ni, Cr and Mn were used in combination with several photometric reagents. It was found that the instrument yielded concentration measurements which were usually within a few percent of the correct concentration. These results are comparable to reported data obtained with conventional instruments for similar measurements. The application of the instrument for simultaneous determination in flow-injection analysis employing rapid computer controlled switching of the light-emitting diodes is also demonstrated. A limitation in the use of light-emitting diodes for the simultaneous determination was found to arise from the fact that in some instances non-linear calibration curves are obtained when employing light-emitting diodes as light sources. This occurs when the absorptivity of the measured compound changes over the emission band of the diodes. Multiple regression analysis is then not easily possible. Received: 16 September 1996/Revised: 14 October 1996/Accepted: 16 October 1996     

Determination of lead in wines by hydride generation atomic absorption spectrometry.

The optimization of lead hydride generation in aqueous ethanolic media and the influence on its generation of the wine components, both white and red, have been studied. These interferences were overcome by careful control of the parameters affecting hydride generation and the procedure was applied to the determination of Pb in wines. The method is fast, accurate and sensitive and can be used to quantify 24 ppb of Pb in wines.     

The structures of fluorides. XV. Neutron diffraction-kubic harmonic profile analysis of the body-centered cubic phase of sulfur hexafluoride at 193°K

Sulfur hexafluoride has a body-centered cubic phase (a = 5.915(3) Å) between its melting point (222.4°K) and 93°K, below which a lower symmetry phase exists. NMR studies show that in both phases there is rapid reorientation of the sulfur hexafluoride molecules. From a neutron diffraction pattern collected at 193°K with λ = 1.086 Å, the data were not satisfied by a model with a spherically symmetrical fluorine density nor by a refinement with conventional ellipsoidal-shaped atoms. The latter gave systematically low S-F distances and abnormally high β_ij thermal factors. Good agreement was obtained by a combination of Kubic Harmonics with full-matrix least-squares analysis of the neutron profile pattern. The refinement was made with one variable Kubic Harmonic coefficient a₂ = 5.94(11), with $\text{R}{}_{\mathrm{w}}\text{= {}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{∑ wy}{}_0{}^2\text{}}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.079}$ and $\text{χ}{}^2\text{=}\text{∑ w[y}{}_0\text{? (}\text{1}\text{s}\text{)y}{}_{\mathrm{c}}\text{]}{}^2\text{(NO-NV)}\text{= = 1.2}$. Only four least-squares variables were required with 225 observations in the range of one or more hkl reflections to 2θ = 58.3°. AS-F distance of 1.542(4) Å, obtained from the neutron diffraction data, is in good agreement with the reported value of 1.564(10) Å found from electron diffraction measurements of the vapor. The disordered fluorine distribution has broad maxima on the cell edges similar to those found in the plastic cubic phases of MoF₆ and WF₆.     

The determination of oxygen in silicon by alpha and helium-3 activation analysis

A non-destructive analytical method for oxygen in silicon by both helium-3 and α-particle activation analysis was applied to different samples, containing 0.05–10 p.p.m. of oxygen. The accuracy and precision of the method were studied. For concentrations above 1 p.p.m., the average coefficient of variation is about 6% for α-activation and 13% for helium-3 activation. For concentrations of about 60 p.p.b., the corresponding figure is about 20%. The results of both methods, which agree within 8%, are compared to infrared analysis. The determination limit of the method is 4 p.p.b. for helium-3 activation and 22 p.p.b. for α-activation.     

Analysis of aerosols at the bosporus bridge of Istanbul

Air samples collected at the second Bosporus bridge of Istanbul which carries a heavy traffic load between Asia and Europe, were analyzed for 22 elements by the INAA method. Pb, Cd and Fe concentrations in the samples were determined by AAS. Iron concentrations were used as a cross check between the two methods. In order to define the enrichment factors for the elements in the bridge area, a sample collected from our university campus which can be considered as a rural site, was also analyzed. Differences were observed especially for Br, Al, Mg, Ti, Cu and Na between the two sites. Based on the results of the samples from the bridge, we got a value of 0.58(16) for the Br/Pb-ratio.     

SPECTRA AND EXTINCTION COEFFICIENTS OF NEAR-INFRARED ABSORPTION BANDS IN MEMBRANES OF Rhodobacter sphaeroides MUTANTS LACKING LIGHT-HARVESTING AND REACTION CENTER COMPLEXES

Abstract— Membranes from Rhodobacter (formerly Rhodopseudomonas) sphaeroides mutant strains that lack one or more of the bacteriochlorophyll a (BChl)-protein complexes were used to obtain spectra and molar extinction coefficients of the near-IR absorption bands. The strains examined were NF57 which lacks the B875 light-harvesting and reaction center complexes, and M21 which lacks the B800–850light-harvesting complex. The extinction coefficients obtained for the B800, B850 and B875 bands were 226 ± 10, 170 ± 5, and 118 ± 5 m M ^-1cm^-1, respectively, in reasonable agreement with values reported for detergent-isolated complexes (Clayton, R. K. and B. J. Clayton, Proc. Natl. Acad. Sci. USA 78 ,5583–5587, 1981). The results also demonstrated that detergent solubilization altered the spectra, causing a band broadening on the blue side of the B875 and B800 peaks. The data obtained from the analysis of the mutant strains were used for deconvolution of the BChl species in membranes of the wild-type. A short BASIC computer program for performing this deconvolution is included.     

Micromethod for the analysis of the four commonly used antiepileptic drugs using a jet tube column

We describe a simple method for the determination of phenobarbital, diphenylhydantoin, carbamazepine, and primidone in serum, by use of gas-liquid chromatography with temperature programming. The methylated derivatives of these anticonvulsants were well resolved, as was 5-(p-methylphenyl)-5-phenylhydantoin, the internal standard. In this procedure we used the jet tube for separation of the drug from the serum. The proposed procedure requires only 100 μl of serum and can be done in less than 30 min. The lower limit of detection for each of the drugs is 0.5 mg/liter. Analytical recoveries of drug from serum were excellent and peak height and concentration were linearly related up to twice the toxic concentration for serum.     

Stable gaseous aziridinium ions

Gaseous protonated aziridine ions are produced at the threshold from β-phenoxyethylamine molecular ions. The evidence for this is collisional activation spectra, using various precursors (including labelled analogues) under electron impact and field ionization conditions. Partial conversion to the acyclic \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm CH}_{\rm 3} {\rm CH = }\mathop {\rm N}\limits^ + {\rm H}_{\rm 2} $\end{document} isomer occurs at higher electron energies and is rationalized by means of a potential energy surface constructed from energetic data.