Spectroscopic evidence for the intermediacy of a 6-R-2,4-diazabicyclo-[3.1.0]hex-2-(3)ene in the photoisomerization of 4-R-1,4-(3,4)-dihydropyrimidines

¹H- and ¹³C-nmr spectroscopy is presented showing that photolysis of 4-(p-trifluoromethylphenyl)-1,4-(3,4)-dihydropyrimidine yields 6-(p-trifluoromethylphenyl)-2,4-diazabicyclo[3.1.0]hex-2-(3)ene.     

The determination of all the platinum group elements and gold in rocks and ore by neutron activation analysis after preconcentration by a nickel sulphide fire-assay technique on large samples

The noble metals are inhomogeneously distributed in sulphide ores and their host rocks. It is therefore necessary to analyse large sample sizes to obtain representative analyses. A nickel sulphide fire assay technique has been adapted to extract the noble metals from a large sample size (50 g) into a nickel sulphide button. Subsequently the fire assay button is dissolved in hydrochloric acid and the solution is filtered. The noble metal residue retained on the filter paper is analysed quantitatively by i.n.a.a. techniques. This method is rapid, relatively inexpensive and has better sensitivities for all the noble metals than other analytical techniques.     

Investigations on the conditional kinetic and thermodynamic stability of aquatic humic substance-metal complexes by means of EDTA exchange, ultrafiltration and atomic spectrometry

The conditional metal availability and the kinetic stability of humic substance-metal species in humic-rich waters (e.g. bog water) was characterized by means of EDTA exchange. For this purpose a combined procedure consisting of time-controlled ligand exchange by EDTA, species differentiation by a fast single-stage tangential-flow ultrafiltration (TF-UF) technique (cut-off 1 kDa) and sensitive atomic spectrometry methods (e.g. AAS, ICP-OES, TXRF) was developed. The kinetics and the yield of the EDTA exchange served as operational parameters for assessing the kinetic stability and EDTA availability of HS-metal species, respectively. Considerable fractions of natural HS-metal species studied were shown to be EDTA-inert (e.g. 31% of the total Fe, 44% of the total Al) even after long reaction times (48 h), in contrast to artificial ones formed in solutions of isolated HS. Moreover, the conditional thermodynamic stability of HS-metal complexes formed by successive loading of an aquatic reference HS (HO14) with a number of heavy metal ions (e.g. Cr(III), Cu(II), Fe(III), Mn(II), Zn(II)) was also evaluated discriminating the free metal concentrations by means of TF-UF. In addition, from the loading isotherms obtained conditional complexation capacities could be derived for the studied HS exhibiting the order Fe(III)>Cu(II)>Cr(III)>Co(II)>Mn(II).     

Infrared,raman and nmr study of (Ch2CH)3Snx compounds (X = Cl,Br, I)

The infrared, Raman and (¹H, ¹³C) NMR spectra of trivinyltin chloride, bromide and iodide have been analyzed and discussed. The vibrational assignment has been confirmed by an approximate normal coordinate analysis. Evidence has been found for a marked influence of the X substituent on the tin-carbon bond due to isovalent rehybridization. Variations in the π electron system of the vinyl group are hardly significant.     

The molecular structure of cis- and trans-1,2-difluoro-ethene: An electron diffraction study

The molecular structure of cis- and trans-1,2-difluoroethene was studied in the gas phase by electron diffraction, using the sector-microphotometer technique. The molecules are planar. For trans-difluoroethene the geometrical parameters are: C-F bond: 1.338(0.003) Å; CC bond: 1.320(0.009) Å; C-H bond: 1.088(0.004) Å, ∠CCF 119.8°(0.2°); ∠CCH: 125° (1.2°). For cis-difluoroethene: C-F bond: 1.332(0.003) Å; CC bond: 1.311(0.008) Å; C-H bond: 1.100(0.003) Å; ∠CCF: 122.5°(0.2°); ∠CCH:127.0 °(2.3°).     

Analysis of organic quaternary ammonium salts by LAMMA

Summary The application of the laser microprobe mass analyser (LAMMA) to several acyclic quaternary ammonium salts with aliphatic and aromatic substituents was investigated. The LAMMA spectra share some typical features with the ones, obtained by mass spectrometric (MS) analysis using soft ionisation techniques, e. g. the intact cations are detected as well as the iminium ions, issued from their decomposition. However, as a result of the abundant fragmentation and because of the presence of additional characteristic peaks, LAMMA spectra become largely comparable to the ones, recorded on a conventional MS with electron impact-ionisation and sample introduction by direct probe, though it is well known that the latter method induces thermal degradation of these salts and consequently only allows for the detection of the corresponding decomposition products.

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Analyse organischer quarternärer Ammoniumsalze mittels LAMMA

Zusammenfassung Die Anwendung des Laser-Mikrosonden-Massen-Analysators (LAMMA) zur Charakterisierung verschiedener acyklischer quarternärer Ammonium-salze mit aliphatischen und aromatischen Substituenten wurde untersucht. Die LAMMA-Spektren zeigen charakteristische Merkmale jener Spektren, die durch weiche Ionisierungstechniken in der Massenspektrometrie erhalten werden: z. B. werden intakte Kationen sowie Imin-Ionen detektiert. Als Folge der weitgehenden Fragmentierung und wegen zahlreicher zusätzlicher Peaks sind LAMMA-Spektren jenen Spektren sehr ähnlich, die durch Elektronenstoß-Ionisation und Direkteinführung der Probe erzeugt werden. Allerdings ist bekannt, daß die letztere Methode einen starken Abbau von Salzen bewirkt und daher nur den Nachweis von Zerfallsprodukten zuläßt.

     

Determination of iron(II) and iron(III) by flow injection and amperometric detection with a glassy carbon electrode

Flow injection analysis can be used for the determination of both iron(II) and iron(III) with an amperometric detector. The flow-through cell contains a glassy carbon electrode. Selection of the appropriate voltammetric technique, choice of the indication potentials, sample size, composition of the carrier stream, etc., are discussed. The limit of determination is about 10^-6 M; the calibration curves are linear in the concentration ranges 10^-3–10^-5 M for iron(III) and 5 × 10^-4–10^-5 M for iron(II). To illustrate the potentialities of the proposed method, standard rocks have been analysed.     

Purification of adipoyl-7-amino-3-deacetoxycephalosporanic acid from fermentation broth using stepwise elution with a synergistically adsorbed modulator

Multicomponent adsorption data of a fermentation broth containing adipoyl-7-amino-3-deacetoxycephalosporanic acid (adipoyl-7-ADCA), a cephalosporin precursor for 7-ADCA, and two key impurities, alpha-hydroxyadipoyl-7-ADCA and alpha-aminoadipoyl-7-ADCA were obtained from batch equilibrium and frontal chromatography tests. Amberlite XAD-1600 was chosen as the resin. A rate model was applied to simulate the chromatograms. An alkaline buffer, which by itself has no affinity for the resin, was used as the eluent. The widely used reversed-phase modulator model is inaccurate in explaining the stepwise elution data. A new model, the induced competition model, has been developed to account for apparent retention of the buffer in the presence of adsorbed species. Close agreement between the simulations and the data was achieved with the new model.     

Water analysis by spark-source mass-spectrometry after preconcentration on activated carbon

For trace analyses of environmental waters, spark-source mass-spectrometry has been combined with a preconcentration procedure involving chelation of the dissolved trace elements with oxine and subsequent adsorption of the oxinates and naturally occurring organic and colloidal metal species onto activated carbon. The activated carbon is filtered off and ashed at low temperature. The residue is dissolved, an internal standard and pure graphite are added and, after drying, the electrodes are prepared. The photographically recorded mass spectrum is evaluated by a suitable computer routine. The error of the procedure is around 30%. While this preconcentration and analysis procedure is capable of measuring about 40 elements quantitatively, in practice 10-25 trace elements are determined simultaneously above the 0.1-mug/l. detection limit, as is illustrated by analyses of drinking water, surface and ground water samples. Although a sophisticated technique, SSMS can be considered for regular panoramic survey analyses.