Automated chemical separations in routine activation analysis

In recent years increased information is required about the distribution of elements at low concentration levels in the biosphere. Neutron activation analysis can play an important role if it can supply many data at relatively low cost. As some of the concentrations are too low for determination by non-destructive techniques, equipment for chemical separations on a routine basis is necessary. For environmental studies a separation scheme has been developed successfully for arsenic, antimony, cadmium, copper, mercury, selenium and zinc. It is based on a combination of distillation and ion-exchange. Special attention is paid to the prevention of interference from bromine and sodium. Additional information about chromium, cobalt, nickel and tungsten can easily be obtained. Experience gathered with an automated instrument for fifty samples a week is described.     

A photometric detector based on a blue light-emitting diode

The suitability of blue light-emitting diodes as radiation sources in molecular absorption spectroscopy was evaluated. Electronic as well as spectral considerations are discussed. A transducer based on a blue light-emitting diode and a photodiode is described which yields direct absorbance readings by passing the photocurrent to an integrated circuit logarithmic converter. The performance of this device was tested for commonly used spectrophotometric procedures for Cr, Mn, Zn, Fe and Cl and compared with conventional molecular absorption spectroscopy. Also investigated was the application of the transducer as a detector in flow-injection analysis.     

Electronic absorption and MCD spectra for Pt(AuPPh3)8(2+) and Au(AuPPh3)8(3+) cluster complexes in poly(methyl methacrylate) thin films at 295 and 10 K

Electronic absorption and 8 T magnetic circular dichroism (MCD) spectra are reported for nitrate salts of Pt(AuPPh3)8(2+) and Au(AuPPh3)8(3+) in poly(methyl methacrylate) (PMM) thin films at 295 and 10 K in the vis-UV region from 1.6 to 3.6 microm(-1) (1 microm(-1) = 10(4) cm(-1). Enhanced resolution is observed at low temperature, especially for Pt(AuPPh3)8(2+), which emphasizes the differences in the nature of the low-energy excited configurations and states between Pt(AuPPh3)8(2+) and Au(AuPPh3)8(3+). The absorption and MCD spectra for Pt(AuPPh3)8(2+) are interpreted in terms of a combination of excitations from filled Pt 5d orbitals to empty Au framework 6s orbitals and intraframework Au8(2+) (IF) transitions, whereas the spectra for Au(AuPPh3)8(3+) are ascribed entirely to Au IF transitions.     

Arsenic speciation by capillary gas-liquid chromatography

Specific environmentally significant arsenic compounds are determined by capillary gas-liquid chromatography. Inorganic (arsenite, arsenate) and organic (monomethylarsonate, dimethylarsinate) arsenicals are measured as the corresponding methylthioglycolate derivatives, which are simultaneously separated on wide-bore borosilicate glass and fused-silica columns under conditions of temperature programming. Inorganic arsenate and arsenite cannot be differentiated by the derivatization technique. Flame-ionization and electron-capture detection are evaluated. A simple and rapid sample preparation procedure is used for water, urine, blood, and tissue.     

Chemical fractionation in the solar system

The cosmochemical and geochemical history of planetary material is reflected in relative and absolute abundances of two groups of trace elements; siderophiles and volatiles. Many of these elements can be determined at the requires levels only by radiochemical neutron activation analysis. The abundance patterns of elements in chondritic meteorites result from condensation processes in the solar nebula. The composition of planetisimals which bombarded the Moon is characterized from trace elements in lunar breccias, and is also related to nebula processes. Trace elements in anorthosites and basalts from Earth and Moon suggest that the Moon is refractory-rich and volatile-poor relative to the Earth.     

High-speed liquid chromatography of polychlorinated biphenyls and related compounds.

High-speed liquid chromatography in the system silica gel-dry n-hexane has been used to characterize the behaviour of a series of commercially available mixtures of chlorinated biphenyls, viz., Aroclor 1221-1268. An attempt has been made to assign a large number of peaks in the chromatograms of the Aroclors to the individual constituents. To this end, retention times and UV spectra were recorded for 47 polychlorinated biphenyls. The dependence of retention and spectral characteristics on the chlorine content of the substituted biphenyls is discussed     

Internal molecular disorder in the nematic and smectic phases of thermotropic liquid crystals studied by NMR SPDE experiments

The recently developed NMR SPDE experiment is shown to provide a new and particularly convenient technique for probing the conformational dynamics of mesogens in thermotropic liquid crystals. Measurements have been made in the nematic and smectic phases of the 4,4′-di-n-alkoxyazoxybenzenes. It is shown for the first time that the internal disorder of the alkyl end chains is intimately related to the molecular organization of these mesophases.     

Inverse Pulspolarographie am h?ngenden Quecksilbertropfen

Zusammenfassung Die inverse Voltammetrie am hängenden Quecksilbertropfen mit pulspolarographischer Aufzeichnung der anodischen Auflösungsströme wird auf ihre Leistungsfähigkeit untersucht. 10^–9 M Lösungen von Cu, Pb, Cd, Zn können im Routinebetrieb analysiert werden. In Alkalisalzmatrices sind Direktbestimmungen der Schwermetalle im 10^–7 bis 10^–8%-Bereich möglich. Die Nachweisgrenze für Cd beträgt 5 · 10^–11 Mol/l. Die Empfindlichkeit der Methode wird mit derjenigen verwandter voltammetrischer Verfahren verglichen.

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Anodic stripping pulse polarography at the hanging mercury drop electrodeDetermination of Cu, Pb, Cd and Zn

The efficiency of anodic stripping pulse polarography at the H.M.D.E. is tested. In routine work the analysis of 10^–9 M solutions of Cu, Pb, Cd, Zn offers no difficulty. The determination of the elements in alkali salts in the 10^–7 to 10^–8% range is possible. The detection limit for Cd was found to be 5×10^–11 M. The sensitivity of the method was compared with those of related voltammetric techniques.

     

Preparative gas chromatography of volatile metal compounds-I Separation of aluminium, chromium and iron beta-diketonates

The analytical gas chromatography of a range of fluorinated and unfluorinated beta-diketonates of aluminium, chromium and iron has been studied m detail and conditions have been established for their complete separation; the complexes of trifluoroacetylpivaloylmethane show the best characteristics for this purpose. A range of liquid phases and column conditions have been considered and Apiezon substrates have been shown to give optimal resolution. The technique has been extended to a preparative scale with up to 0.1-g chelate samples, and the efficiency of the process demonstrated by the removal of 2% proportions of two metal complexes from a sample of the third. Implications of the technique for the purification of metals are discussed.     

A particle growth theory for heterogeneous Ziegler polymerization

Samples of “as produced” polypropylene particles at progressively higher yield levels (grams polymer/gram catalyst) were sliced and examined by electron microscopy. In the polymerization of propylene with the TiCl₃–(C₂H₅)₂AlCl catalyst system the catalyst breaks up immediately into basic 100–1000 Å particles. As the yield increases, the catalyst particles gradually disappear and finally become completely dispersed in the polymer particle. These results are compatible with a theory which views the catalyst as a porous crystal containing a single species of active sites uniformly distributed. As polymerization progresses, all sites should eventually initiate a polymer chain whose length should be inversely proportional to the depth of the site below the surface of the particle. Two apparently equivalent statistical models were developed on the basis of this concept. Both models predict a slow increase in the X?_w/X?_n ration (Q) with increasing molecular weight, after an initial rapid increase. The most useful of these models states that Q is equal to the sum of X?_w terms of the simple harmonic series, and that a complete spectrum of x-mers should be present in the product. This agrees satisfactorily with analytically determined values.