Primary methods of measurement in chemical analysis

 Primary methods of measurement have a central function in metrology. They are an essential component in the realisation of the SI units and therefore are indispensable for establishing traceability of measurements of all kinds of physical quantities to the corresponding SI units. This is also true for chemical analysis. Gravimetry, titrimetry, coulometry, and isotope dilution mass spectrometry (IDMS) are evaluated with regard to their potential to be primary methods according to a general definition of primary methods recently given by the Comité Consultatif pour la Quantité de Matière (CCQM). Optical absorption spectrometry and methods based on colligative properties are also considered. A general scheme for establishing traceability of chemical measurements to the SI units using primary methods is discussed. Received: 17 April 1997 · Accepted: 9 August 1997     

Alignment of H(2p) in H-He,Ne, Ar collisions

The integral alignmentA ₂₀ was investigated for H(2p) excitation in H-He, Ne, Ar collisions at incident energies of 1–25 keV. The experimental results are compared with theoretical calculations based on different theoretical models. Calculations which do not account for the quasi-molecular aspect of the collision process are at variance with the experimental data below incident energies of 10 keV. Above 15 keV, fair agreement is obtained with calculations which include simultaneous excitation of both projectile and target.     

Effects of <Emphasis Type="Italic">L</Emphasis>-Carnitine on Sucrose-Induced Hyperlipidaemia

Summary. L-Carnitine, L-(−)-β-hydroxy-γ-trimethylaminobutyrate, plays an important role as a factor necessary for the transport of long-chain fatty acids into the mitochondria. In order to investigate the influence of L-carnitine on hyperlipidaemias, the experimental model of the sucrose-induced hypertriglyceridaemia of the rat was used. In these experiments L-carnitine in the dose of 11 mg per day and 100 g body weight (over the period of 1 week) was able to antagonize the sucrose-induced hypertriglyceridaemia and the increase of serum free fatty acid level in female rats of the Wistar strain. Carnitine administration did not change the activities of lipogenic enzymes and fatty acid synthesis in the liver. However, L-carnitine increases the rate of hepatic fatty acid oxidation. Our results indicate a hypotriglyceridemic and free fatty acid lowering effect of L-carnitine, and suggest the use of this compound in the therapy of hyperlipidaemias.     

Festköperreaktionen in Chalkogenidsystemen. III. Bestimmung der Aktivierungsenergie von Pulvereaktionen aus Leitfähigkeitsglowkurven

In the case of the formation of thiospinels (MnCr₂S₄, ZnCr₂S₄ and CdCr₂S₄) a simple method for the determination of the activation energy of solid state reactions in polycrystalline samples by means of conductivity measurements is shown. The maxima and minima of conductivity (glow curve maxima and -minima) in the σ vs T-curves got by annealing with linearly increasing temperature are shifted towards higher temperatures with increasing rate of heating(q). By plotting ln (q/T) vs 1/T_σmax a straight line results. The activation energy of the reaction may be deduced from the slope of this straight line in analogy to the determination of the trap depth of electrons from glow curves observed in thermoluminescence.     

Electrosorption of sodium cellulose sulfates with different substitution patterns

Various types of sodium cellulose sulfate (SCS), dissolved in a 1M LiCl solution, were investigated by alternating current (AC)polarography. The SCS samples differed in the degree of substitution (DS), thedistribution of substituents within the anhydroglucose unit (AGU), and alongthechain, due to the method of synthesis. The goal was to study theelectrosorptionbehavior, characterized by the shape of the desorption wave in the polarogram,as a function of the chemical structure of the SCS samples. The shape of thedesorption wave reflects domains of different substitution. A superimpositionofparameters like DS and pattern of substitution on the electrosorption behaviorwas observed. The AC polarography method described can be used as a tool todistinguish between an even or uneven distribution of substituents along thecellulose chain.     

Strukturuntersuchungen an 4-methyl-6-phenyl-2-(thiobenzoylmethylen)-2H-thiapyran

The structure of 4-methyl-6-phenyl-2-(thiobenzoylmethylene)-2H-thiapyran (1) was investigated by ESCA, X-ray analysis and quantum chemical calculations. The no-bond interaction between the sulphur atoms (R_s…s = 3.000(1) Å) is caused by π-type interaction rather than by Coulomb-type interaction.     

Quantitative evaluation of interference reactions in photon activation analysis

Interferences of different types (competing reactions, overlapping photons emission energies etc.) occur more frequently during activation analysis with high energy exciting radiation that in conventional thermal neutron activation. Three main types of interference in high energy photon activation analysis (PAA) have been determined quantitatively, using experimentally obtained data exclusively. Based on the results presented, it is possible in many critical cases to improve significantly the accuracy of analysis results obtained by PAA.     

Alignment and orientation effects in resonant charge exchange from laser excited Na*(3p)

A collisional alignment and orientation study with planar symmetry is described, determining the complete density matrix for resonant charge transfer from laser excited atoms. Results are reported for the Na⁺+Na*(3p) system over the collision energy rangeE _c.m.=50?100 eV. We communicate the optimal alignment angle γ and linear polarisationP _l ⁺ of the charge cloud as well as its relative height ρ₀₀ and the angular momentumL _⊥ ⁺ transferred in the collision as a function of the scattering angle. For preparation of the sodium 3p orbital in the scattering plane (positive reflection symmetry) we observe that at small reduced scattering angles (<20 eV°) the preparation of apσ at large internuclear distances contributes most to the scattering intensity whereas at larger reduced scattering angles (>60 eV°) apπ⁺ preparation is more important. In contrast, preparation of thepπ^? orbital (perpendicular to the scattering plane) is large at small and vanishes at larger scattering angles. We conclude that orbital following cannot be assumed in this resonant charge transfer process. The angular momentum transfer is observed to be small, indicating only little coherence in the process, but shows nevertheless an interesting behaviour as a function of scattering angle.     

Electron impact ionization mass spectra of 2,4,5,5-tetrasubstituted 1,2,4-triazolidine-3-thiones. The effect of the ethoxycarbonyl group at position 4

The electron impact ionization mass spectra of 2,4,5,5-tetrasubstituted 1,2,4-triazolidine-3-thiones studied confirmed that the substituent at position 4 has the most dramatic influence on the fragmentation pattern. When the substituent is a methylallyl group the molecular ions exhibit four main routes of fragmentation, but when it is an ethoxycarbonyl/acetyl or a methyl group these direct decompositions of the molecular ion become less abundant. Interestingly all 4-ethoxycarbonyl derivatives and the 4-acetyl derivative exhibited the ions [M-R⁴-COOC₂H₄]⁺ and [M-R⁴-COCH₂]⁺, respectively, with the same composition.     

Mobility of muons in Cu below 2 K

We have performed transverse fieldSR experiments on several different samples of copper in the temperature range below 2 K, including isotope separated Cu and impurity doped polycrystalline Cu.We do not observe any strong effect of the isotope composition of the sample. A⁶³Cu and a natural Cu sample of identical purity both yield 0.16s^–1 for the low-temperature plateau, while an increased linewidth in the⁶⁵Cu case may be related to the strong effects of Fe impurities.Careful transverse field measurements on large single crystals at 0.08 K reveal non-Gaussian lineshapes in accordance with the picture of diffusing muons at this temperature. This allows us to reject several of the existing models for muon behaviour in copper below 2 K.