Spectrophotometric determination of organic nitrogen by a modified Lassaigne method and its application to meat products and baby food

A modified Lassaigne method was developed for N determination based on fusion of the organic substance with metallic Na, conversion of the cyanide in the aqueous leachate to thiocyanate by ammonium polysulfide treatment, and colorimetric measurement of the thiocyanate formed by the addition of excessive ferric ions in acidic medium. The mean molar absorptivity of the Fe(NCS)2+ complex at 480 nm is 2.96 x 10(3) L/mol x cm, enabling quantitation of 0.25-7.72 ppm N (linear range) in the final solution. The relative amounts of Na, (NH4)2S2, and Fe(III) with respect to nitrogen in the analyte were optimized. The developed method was successfully applied to the determination of N in various brands of baby food, and it was compared statistically with the conventional Kjeldahl and elemental analysis methods. Protein nitrogen in a number of meat products was also precisely determined by the developed method. Thus, the total digestion time of the conventional Kjeldahl method was reduced considerably (e.g., to approximately 15 min for a dried sample) with a relatively simple spectrophotometric method requiring no sophisticated instrumentation.     

Calculation of current densities using gauge-including atomic orbitals

A method for calculating the various components of the magnetically induced current-density tensor using gauge-including atomic orbitals is described. The method is formulated in the framework of analytical derivative theory, thus enabling implementation at the Hartree-Fock self-consistent-field (HF-SCF) as well as at electron-correlated levels. First-order induced current densities have been computed up to the coupled-cluster singles and doubles level (CCSD) augmented by a perturbative treatment of triple excitations [CCSD(T)] for carbon dioxide and benzene and up to the full coupled-cluster singles, doubles, and triples (CCSDT) level in the case of ozone. The applicability of the gauge including magnetically induced current method to larger molecules is demonstrated by computing first-order current densities for porphin and hexabenzocoronene at the HF-SCF and density-functional theory level. Furthermore, a scheme for obtaining quantitative values for the induced currents in a molecule via numerical integration over the current flow is presented. For benzene, a perpendicular magnetic field induces a (field dependent) ring current of 12.8 nA T(-1) at the HF-SCF level using a triple-zeta basis set augmented with polarization functions (TZP). At the CCSD(T)/TZP level the induced current was found to be 11.4 nA T(-1). Gauge invariance and its relation to charge-current conservation is discussed.     

A parallel implementation of the COLUMBUS multireference configuration interaction program

Summary In this work a parallel implementation of the COLUMBUS MRSDCI program system is presented. A coarse grain parallelization approach using message passing via the portable toolkit TCGMSG is used. The program is very well portable and runs on shared memory machines like the Cray Y-MP, Alliant FX/2800 or Convex C2 and on distributed memory machines like the iPSC/860. Further implementations on a network of workstations and on the Intel Touchstone Delta are in progress. Overall, results are quite satisfactory considering the complexity and the prodigious requirements, especially the I/O bandwidth, of MRCI programs in general. For our largest test case we obtain a speedup of a factor of 7.2 on an eight processor Cray Y-MP for that section of the program (hamiltonian matrix times trial vector product) which has been parallelized. The speedup for one complete diagonalization iteration amounts to 5.9. An absolute speed close to 1 GFLOPS is found. Results for the iPSC/860 show that ordinary disk I/O is certainly not sufficient in order to guarantee a satisfactory performance. As a solution for that problem, the implementation of a fully asynchronous distributed-memory model for certain data files is in preparation. On leave from: Bereich Informatik, Universität Leipzig, Augustusplatz 10/11, O-7010 Leipzig, Germany     

Development of solid phase reactors for continuous detection systems

Summary The methodical development of a solid phase reactor (SPR) as an integrated part of a chemical reaction detector is described for manganese. The preparation of a suitable reactor packing material byin situ precipitation of lead-dioxide on silica gel permits running the SPR in low pressure ranges. Divalent manganese and also higher oxidation states of the metal are oxidized to permanganate in the reactor. Thus, an isoformation of all manganese species originally present in the sample takes place. As the direct photometrical detection of permanganate is not sensitive enough for trace analyses, the heterogeneous oxidation system is followed by a homogeneous chemical reaction system, in which permanganate reacts with leucomalachite green. The resulting blue-green dye is detected photometrically at 620 nm.The application of a column switching technique allows the continuous enrichment, separation, and determination of manganese down to the nanogram level with high precision and also a differentiation between divalent manganese and three- to seven- valent manganese.This chemical reaction detector can be used also for continuous detection in chromatography, especially HPLC. The detection limit is 10 ng/ml.

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Entwicklung eines Festbettreaktors für kontinuierliche Nachweissysteme. Teil I

Zusammenfassung Die methodische Entwicklung eines Festbettreaktors als integrierter Bestandteil eines chemischen Reaktionsdetektors wird beschrieben. Die Herstellung einer geeigneten Reaktorpackung durch Ausfällen von Bleidioxid auf Kieselgel erlaubt den Betrieb des Festbettreaktors im Niederdruckbereich. Zweiwertiges Mangan sowie höhere Oxydationszustände des Metalls werden im Reaktor zum Permanganat-Ion oxydiert, so daß eine Isoformierung aller in der Probe vorhandenen Mangan-Spezies stattfindet. Da die photometrische Detektion des Permanganat-Ions für spurenanalytische Messungen nicht ausreichend empfindlich ist, wird im Anschluß an den heterogenen Bleidioxid-Reaktor ein homogenes chemisches Reaktions-system betrieben, in dem das Permanganat-Ion mit Leukomalachitgrün umgesetzt wird. Dabei entsteht der blaugrüne Farbstoff Malachitgrün, der bei 620 nm photometrisch gemessen wird.Die Verwendung einer Säulenschalttechnik ermöglicht eine kontinuierliche Anreicherung, Abtrennung und Bestimmung von Manganspuren bis in den Nanogramm-Bereich mit hoher Genauigkeit, sowie eine Differenzierung zwischen zweiwertigen Mangan-Spezies einerseits und dreibis siebenwertigen Oxydationsstufen andererseits.Der vorgestellte chemische Reaktionsdetektor kann auch zur kontinuierlichen Chromatographie-Detektion benutzt werden. Die Nachweisgrenze beträgt 10 ng/ml.

     

IR-spektroskopische Untersuchungen an N-Alkyliden-alkylaminen und N-(Trimethylsilylethyliden)-alkylaminen

I.R. Spectroscopic Investigations on N-Alkylidene-alkylamines and N-(Trimethylsilylethylidene)-alkylamines The position of the C?N-stretching vibration of N-Alkylidene-alkylamines and N-(Trimethylsilylethylidene)-alkylamines in carbon tetrachloride has been determined. The relative basicity has been measured for this compounds by means of the ^vC-D band shift of CDCl₃ associated to the azomethine. The data are discussed with respect to the specific influence of the trimethylsilyl group.     

Paleoenvironmental organic indicators in Eocene paleosols from Arctic Canada

Summary The analytical potential of the combination of solid state NMR and soft ionization mass spectrometry for direct investigations of complex organic matter in soils without chemical pretreatment is demonstrated. The results show that the Oh horizon of a Gleysolic paleosol (±45 Ma) from the Canadian Arctic consists mainly of components of cuticular waxes which include 10-nonacosanol, C₁₅–C₃₆ n-fatty acids, C₄₄–C₇₅ n-alkyl monoesters and C₆₀–C₇₆ diesters. It is likely that these waxes originated from the coniferous and deciduous vegetation which dominated this area when these soils were formed and that the climate was warm and moist.     

Vergleichende Untersuchungen an polarographischen Analysenverfahren

The universal voltammetric instrument, described in part I of this series, is used for comparative studies on the most important polarographic methods, direct current, derivative pulse, simple and phase-sensitive alternating current, double-tone, and harmonic-wave polarography. In general the peak-heights of these methods are influenced in the same measure by the composition of base electrolyte. In single cases characteristic differences are observed.     

Toward direct determination of conformations of protein building units from multidimensional NMR experiments. V. NMR chemical shielding analysis of N-formyl-serinamide,a model for polar side-chain containing peptides

Knowledge of chemical shift-structure relationships could greatly facilitate the NMR chemical shift assignment and structure refinement processes that occur during peptide/protein structure determination via NMR spectroscopy. To determine whether such correlations exist for polar side chain containing amino acid residues the serine dipeptide model, For-L-Ser-NH(2), was studied. Using the GIAO-RHF/6-31+G(d) and GIAO-RHF/TZ2P levels of theory the NMR chemical shifts of all hydrogen ((1)H(N), (1)H(alpha), (1)H(beta1), (1)H(beta2)), carbon ((13)C(alpha), (13)C(beta), (13)C') and nitrogen ((15)N) atoms have been computed for all 44 stable conformers of For-L-Ser-NH(2). An attempt was made to establish correlation between chemical shift of each nucleus and the major conformational variables (omega(0), phi, psi, omega(1), chi,(1) and chi(2)). At both levels of theory a linear correlation can be observed between (1)H(alpha)/phi, (13)C(alpha)/phi, and (13)C(alpha)/psi. These results indicate that the backbone and side-chain structures of For-L-Ser-NH(2) have a strong influence on its chemical shifts.     

Photophysics and redox behavior of chiral transition metal polymers

The absorption and emission spectra, excited-state lifetimes, quantum yields, and electrochemical measurements have been obtained for a new series of chiral complexes based on three different chiral 2,2':6',2' '-terpyridine ligands, (-)-ctpy, (-)-[ctpy-x-ctpy], and (-)-[ctpy-b-ctpy], with one, two, or multiple Ru metal centers. The room-temperature absorption and emission maxima of [[((-)-ctpy)Ru]-(-)-[ctpy-b-ctpy]-[Ru((-)-ctpy)]](PF(6))(4) and ((-)-[ctpy-b-ctpy])-[[Ru((-)-[ctpy-b-ctpy])](PF(6))(2)](n) were shifted to lower energies and also exhibited significantly longer luminescence lifetimes when compared to [Ru((-)-ctpy)(2)](PF(6))(2), [[((-)-ctpy)Ru]-(-)-[ctpy-x-ctpy]-[Ru((-)-ctpy)]](PF(6))(4), and ((-)-[ctpy-x-ctpy])-[[Ru((-)-[ctpy-x-ctpy])](PF(6))(2)](n). In terms of their electrochemical behavior, all of the complexes studied exhibited one Ru-centered and two ligand-centered redox waves and the [[((-)-ctpy)Ru]-(-)-[ctpy-x-ctpy]-[Ru((-)-ctpy)]](PF(6))(4), ((-)-[ctpy-x-ctpy])-[[Ru((-)-[ctpy-x-ctpy])](PF(6))(2)](n), and ((-)-[ctpy-b-ctpy])-[[Ru((-)-[ctpy-b-ctpy])](PF(6))(2)](n)() complexes were found to electrodeposit upon ligand-based reduction. The difference between the formal potentials of the Ru-centered and the first ligand-centered (least negative) waves corresponded linearly with the changes in the observed emission energies. The shifts in energy are discussed using a particle-in-a-box model, and the luminescence lifetimes are discussed in terms of the structure of the excited-state manifold.