High precision retention time measurements in gas chromatography. I. A simple differentiating time printer for large sample sizes

Summary A differentiating time printer (DTP) apparatus has been constructed from standard laboratory equipment by connecting a differentiating CR circuit via an operational amplifier to an electronic temperature regulator that triggers the print out of a line frequency driven register. The electronic resolution is 0.1 s, giving a relative standard deviation _rel, which is determined by the stability of the line frequency at sufficiently long retention times. In Lund this corresponds to a best _rel = 0.02% and to a mean _rel = 0.03%. For late and broad peaks in real GC the noise caused the print-out of extra time values, especially with fronting peaks from ordinary 1/8 columns. However, a comparison with the simultaneously recorded chromatograms was generally sufficient to pick out the proper retention times. For large sample sizes the corrected retention time t increased with peak height, the later the peak in the chromatogram. The In t _n+1 /t _n values from a series of n-paraffins showed good linear correlations with peak height h_n+1 and peak area A_n+1, giving standard deviations around the line approaching that expected from _rel. The accuracy of the system was mainly determined by the effect of a non-zero triggering level on the derived signal and by the time displacement expected from a large time constant. A rough estimate of the time error was made by simulating GC peaks with a cosine wave generator.     

Prediction of precision from signal and noise measurement in liquid chromatography: Mathematical relationship between integration domain and precision

Summary The precision of integration over noisy instrumental output for quantitative analysis is studied. A probability theory is developed to predict the relative standard deviation (RSD) of integration results over an integration domain from one-point integration (peak height measurement) to entire area integration in HPLC. Common integration modes of horizontal zero line and oblique zero line are taken into account, but no peak overlap is assumed. The question of the analytical superiority of peak height measurement or integration for quantitation is answered. In the HPLC apparatus used, the minimum RSD of measurements is found in the integration domain of ca. ±0.5 σ for analytes [peaks are approximated by the Gaussian signal of width, σ (standard deviation)]. The RSD of integration measurements is also shown to depend on the stochastic properties of background noise (uncorrelated noise and correlated 1/f type noise). The theoretical conclusion is verified by Monte Carlo simulation and HPLC experiments for some aromatic compounds. Second Part of series cited as Ref. [1].     

Hochtemperatur-röntgenographische Untersuchungen an manganreichen Mangan—Vanadin-und Mangan—Chrom—Legierungen

Zusammenfassung Die manganreiche Seite der Systeme Mn–V und Mn–Cr wurde hochtemperatur-röntgenographisch untersucht. Im System Mn–V treten bei 90 At% Mn zwei bisher nicht beobachtete Phasen, und , mit -bzw. -Manganstruktur auf. Diese gehören möglicherweise der Klasse der -bzw. -Phasen an. Die -Mischphase besitzt einen größeren Existenzbereich als in der Literatur angegeben. Die Existenz der -Phase Mn₃V, sowie die Phasenzustände bis 80 At% Mn und bei manganreicheren Legierungen unterhalb 700°C werden bestätigt. Das lineare thermische Ausdehnungsverhalten der Phasen , und sowie des -und -Mischkristalls werden angegeben. Für den manganreichen Teil wird ein vorläufiges Zustandsdiagramm entworfen. Im System Mn–Cr konnte in großen Zügen Über-einstimmung mit Literaturangaben gefunden werden. Es wird das lineare thermische Ausdehnungsverhalten der -Phase Mn₃Cr angegeben.

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High temperature X-ray investigation of Mn—rich Mn—V and Mn—Cr alloys

The manganese rich portions of the phase diagrams Mn–V and Mn–Cr have been investigated by means of a high temperature X-ray technique. In the system Mn–V two new phases, and , have been observed with -manganese and -manganese type structure, resp. These phases are probably to be classified as -and -phase. The -manganese solid solution with vanadium has a wider range of homogeneity as compared with previous work. The existence of a -phase Mn₃V and phase equilibria below 700°C reported previously could be confirmed. The linear thermal expansion of the intermetallic compounds , , , the -and -manganese solid solutions with vanadium has been evaluated. A tentative phase diagram for the manganese rich portion is given. The main features of the system Mn–Cr according to previous investigations could be confirmed. The linear thermal expansion of the -phase Mn₃Cr is reported.

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Mit 8 Abbildungen

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Herrn Prof. Dr.Hans Nowotny in Dankbarkeit gewidmet.     

Calculation of two-center zero-field splitting integrals

Two-center zero-field splitting (ZFS) integrals have been calculated by numerical integration of Coulomb repulsion integrals which are evaluated over basic charge distributions as defined by Roothaan in terms of Slater atomic orbitals. The method is applied to the calculation of the ZFS integrals for -, - and - electron interactions on C, N and N⁺ centers. Numerical results are given.

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Zusammenfassung Zweizentren ZFS-Integrale sind mittels numerischer Integration von Coulombintegralen berechnet worden, und zwar die -, -- und --Integrale an C-, N- und N⁺-Zentren. Die numerischen Resultate werden mitgeteilt.

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Résumé Les intégrales bi-centriques de séparation à champ nul (ZFS) ont été calculées par intégration numérique des intégrales de répulsion coulombiennes évaluées pour les distributions de charge fondamentales définies par Roothan en termes d'orbitales atomiques de Slater. La méthode est appliquée au calcul des intégrales ZFS pour les interactions -, - et - sur les centres C, N et N⁺. Résultats numériques.

     

New notions of active surface composition of reforming catalysts

Some peculiarities of adsorption and catalytic properties of electron deficient platinum atoms (Pt) in reforming catalysts are presented. It appears possible to improve catalysts modifying Pt centers with -donor molecules.     

Substituent parameters for radical reactions Cerium(IV) — substituted toluenes — acrylonitrile system

Summary In the present study, a new approach for the determination of ', that is, radical substituent parameter, has been described. The technique is based on two equations, one reported byYamamoto andOtsu and the other byStreitwieser andPerrin. The system used for the determination of the radical substituent parameter (') was Ce(IV) — substituted toluenes — acrylonitrile system. To explain inhibition, it has been suggested that the reaction scheme involves initiation of polymerization by Ce(IV) and termination by primary radical of the substrate. The kinetic expression based on the reaction scheme formulated could explain the unusual observation of a negative intercept found in the plot of [M]/R _p versus 1/[M]. Whereas a plot of log /₀ against ⁺ did not give a straight line, a good linear plot with zero intercept was obtained when log /₀ was plotted against (⁺ + '). This proves the validity of ' values which have been determinded.     

Peak Coincidence Tests in Qualitative Chromatographic Analysis: Taking into Account the Reproducibility of Retention Characteristics

Probabilistic algorithms are proposed for calculating the values of chromatographic peak coincidence. These algorithms take into account the standard deviation of normally distributed retention characteristics () and the selectivity of the tabulated values. At a high selectivity, the 3 value is recommended for the assignment of well-reproducible and widely spaced peaks. In more complicated cases, it is desirable to use values that take into account the number of repeated tests and minimize the integrated probability of errors of first and second kinds, which are associated with a random shift of peaks in chromatographing a sample.     

Correlation of nucleae quadrupole resonance frequencies with some chemical constants in the aliphatic series

Linear relationships are established between the nuclear quadrupole resonance frequencies of alkyl chlorides, RCl, on the one hand, and the pK_a values of RCOOH and RNH₂ as well as the Taft ^* constants, on the other hand. Similar linear correlations were found between the NQR frequencies of the substituted compounds XCH₂Cl and the pK_a of XCH₂COOH, XCH₂NH₂, XCH₂OH, as well as the ^* constants of XCH₂ radicals, where X are electronegative substituents. X substituents with unshared electron pairs (RO, RS, F, Cl, Br) are an exception; nevertheless, the deviation of these points is regular and depends linearly on the resonance parameters _R ⁰ or _R of the X substituents. The relationships can be used for an approximation of the ionization constants of a number of fatty acids, for the calculation of the Taft ^* constants of radicals R and XCH₂ and of the resonance parameters _R ⁰ and _R of X substituents with an accuracy which in many cases is in no way inferior to that of the experimental values, and also for the approximate evaluation of the ionization constants of XCH₂NH₂ amines and XCH₂OH alcohols.     

Quantum-chemical study of allylic compounds with two bonded heavy atoms

It has been shown by the CNDO method that the bathochromic shift of the long-wave absorption band in the transition from allylstannane to compounds of the type C=C-C-Sn-X and C=C-Sn-X (where X is a heavy atom) is connected with the formation of a low-energy vacant *_S-X orbital, localized mainly in the region of the Sn-X chemical bond, and of an occupied _Sn-X orbital, the energy of which is somewhat higher than of the _C-Sn orbital. The dependence of the position of the long-wave absorbance region on conformation is related to the fact that, in planar and nonplanar conformers, the long-wave transitions are of a different type ( * and *, respectively); the bathochromic shift is determined to a large degree by the difference in the energies of the highest occupied MO ( - ) in the s-trans form. In the nonplanar conformers the heavy atom orbitals interact with the -orbital of the ethylene moiety through the bridge group; this leads to a significant delocalization of the HOMO and to a considerable change in its energy. On the other hand, their interaction with the *-orbital in compounds of the C=C-C-Sn-X type is very low and does not favor the delocalization of lower vacant MO. In vinyldistannane the *-orbital is noticeably delocalized, due to the interaction with the *_Sn-Sn orbital in planar and with the *_Sn-Sn orbital in nonplanar conformers.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 3, pp. 636–641, March, 1992.     

Calculation of σ→π* and π→σ* transitions in vinylboranes

Calculations are presented of the energies of the ground and excited and electronic states of ethylene and substituted vinylboranes. The Pople-Segal-Santry method was employed throughout. It is concluded that the excited state of lowest energy in ethylene has * character whilst the lowest energy ultra-violet spectral bands of the latter compounds stem from ^* transitions.

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Zusammenfassung Valenzelektronenrechnungen nach Pople-Segal-Santry wurden für Äthylen und Vinylborane durchgeführt. Danach hat der niedrigste angeregte Zustand von Äthylen ^*-Charakter, während die längstwellige UV-Bande der Vinylborane einem ^* -Übergang entspricht.

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Résumé Calculs de l'énergie pour les états fondamentaux et excités et de l'éthylène et des vinylboranes substitués. Utilisation de la méthode de Pople-Ségal-Santry. L'état excité le plus bas pour l'éthylène résulte d'une transition ^* , alors qu'il résulte d'une transition ^* pour les vinylboranes.

     

Surface charge density on spherical silica particles in aqueous alkali chloride solutions

The results of a systematic investigation on the influence of different alkali ion species on the surface charge density, ₀, of spherical silica particles (AEROSIL 300) in the pH range between 4 and 8 and with electrolyte concentrations from 0.005 M to 0.3 M are presented. The accuracy of the data may be described by a residual deviation,s( ₀ ^m ), including at least four single measurements:s( ₀ ^m )>0.2C/cm². The alkali sequence found for the spherical particles is in agreement with data for porous silica published by other authors.     

Determination of the ratio of the hydrogen and manganese absorption cross sections by the manganese bath technique

The ratio of the hydrogen and manganese neutron absorption cross sections, _H/_Mn, is a most important parameter in the determination of radioactive neutron source strength by the manganese bath technique. The ratio is well measured by observing the change in⁵⁶Mn activity induced in the manganese bath by a fixed neutron source as the manganese concentration of the bath is changed. In the present study, the neutron source was a Maxwellian beam from²⁵²Cf. Concentrations were determined by the two methods: volumetric and gravimetric. The cross section ratio has turned out to be _H/_Mn=0.02506.     

Predissociation lifetime of the 1σ g 2 2σ g diabatic state of He 2 + : a one-channel approach

Summary This work is concerned with the application of a one-channel model to obtaining predissociation lifetimes and transition rates in a system of crossing diabatic states. The calculation focuses on the first shape resonance of the 1 _g ² 2 _g diabatic state of He ₂ ⁺ , which is relatively stable with respect to tunneling. This resonance predissociates as a result of the 1 _g ² 2 _g state being crossed by the 1 _g 1 _u ² dissociative diabatic state near the resonance level. We have estimated its predissociation lifetime to be of the order of 10^–11 s.     

Exponential temperature change in thermal analysis at non-isothermal kinetics

The applying of exponential temperature programming: dT/dt=T orT=T ₀ e ^t in thermal analysis at non-isothermal kinetics is discussed. An approach for the integration of the temperature integral is presented.     

Intensity of the η(C≡C) Bands in the IR Spectra of Acetylene Derivatives and σR 0 Constants of Organosilicon,Organogermanium, and Organotin Substituents

The integral absorptivities of shape-characteristic (CC) bands in the IR spectra of 66 acetylene derivatives RCCX (R = H, Me₃M; X are inorganic and organic substituents) are related by a common linear equation to the _R ⁰ constants of the R and X substituents. The _R R⁰ constants of 10 Alk₃M substituents were calculated. The _R ⁰, _R , and _R ⁺ constants of Me₃M substituents were analyzed. The positive _R ⁰ values (0.12, 0.06, and 0.04 for R = Si, Ge, and Sn, respectively) suggest that in the ground electronic state of Me₃MCCX molecules the resonance acceptor effect of the Me₃M substituents (d, conjugation) prevails over donor (, conjugation). The first effect attenuates and the second enhances as the atomic number of M increases.     

Hyperconjugation of unsymmetrical groups

The interaction of the -bond system with the -electron system in molecules of type {ie427-01} is easily determined for the symmetrical CH₃ group by isolating the -component from the system of three -bonds; CH₃ is thus treated as a C=X quasivinyl group. The theory is extended to unsymmetrical groups.Read at the Symposium on Quantum Chemistry, Palanga, June 1965.     

The electronic structures of urazole,pyrrole, and their ions. The σ-π separability problem

Ab initio all-electron LCGTO-SCF-MO calculations have been made on the 5-membered ring nitrogen heterocycles urazole (C₂H₃N₃O₂), pyrrole (C₄H₅N), and their ion radicals. Wavefunctions were obtained, population analyses made, and electron density contour maps drawn. The results show that for urazole considerable polarity develops in the bonds as a result of a large shift of charge towards the nitrogen atoms at the expense of the carbon and hydrogen atom -electrons with only little effect on the oxygen atom charges. In addition, it is concluded that the -electron approximation should be used with great caution for this type of molecule since the - separability conditions are not well satisfied.

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Zusammenfassung Für die Fünfring-Stickstoffheterocylen Urazol (C₂H₃N₃O₂), Pyrrol (C₄H₅N) und ihre Ionenradikale wurden ab initio Rechnungen nach der LCGTO-SCF-MO-Methode durchgeführt, wobei alle Elektronen berücksichtigt wurden. Die Besetzungszahlen wurden ermittelt und die Elektronendichten graphisch dargestellt. Die Rechnungen zeigen, daß für Urazol eine beträchtliche Polarität in den -Bindungen vorhanden ist. Der Grund dafür liegt in der starken Verschiebung der -Ladung in Richtung des Stickstoffatoms auf Kosten der -Elektronen des Kohlenstoffs und Wasserstoffs. Die -Ladungen am Sauerstoff werden kaum beeinflußt. Von einer -Elektronenapproximation für diese Art von Molekülen wird abgeraten, da die --Separationsbedingungen nur ungenügend erfüllt werden.

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Résumé Calculs ab-initio LCGTO-SCF-MO pour tous les électrons des hétérocycles pentagonaux: urazole (C₂H₃N₃O₂), pyrrole (C₄H₅N) et de leurs ions-radicaux. Après obtention des fonctions d'onde, l'analyse de population est affectuée et les cartes de densité électronique sont dréssées. Les résultats indiquent que l'urazole présente une forte polarité dans les liaisons sigma résultant d'un transfert de charge sigma vers les atomes d'azote aux dépens des atomes de carbone et d'hydrogène et en affectant peu les atomes d'oxygène. De plus, la séparabilité sigma pi n'est pas bien satisfaite dans ce type de molécule.

     

Theoretical electronic transition probabilities of heteronuclear diatomic molecules

Dipole strengths of various heteronuclear diatomic molecules are calculated for high and low energy transitions of one spectral type, 1-1, -. Through the use of increasingly accurate ground state wavefunctions it is possible to display the sensitivity of the transition probabilities to known approximations in the wavefunction. Selfconsistent field and configuration interaction effects are compared and contrasted.

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Zusammenfassung Dipolstärken von zweiatomigen Molekülen mit verschiedenen Kernen wurden für Übergänge vom Typ 1-1, - mit großer und kleiner Energiedifferenz berechnet. In die Funktionen für den Grundzustand war eine unterschiedlich große Anzahl von Konfigurationen einbezogen worden, so daß die Abhängigkeit der Übergangswahrscheinlichkeiten vom Approximationsgrad verfolgt werden konnte. In der Diskussion wurden SCF- und CI-Effekte unterschieden.

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Résumé Les forces d'oscilateurs dipolaires de diverses molécules diatomiques hétéronucléaires sont calculées pour les transitions de basse et haute énergie d'un type spectral 1-1, -. Par utilisation de fonctions d'onde de l'état fondamental de plus en plus précises il est possible de montrer la sensibilité des probabilités de transition aux approximations connues sur la fonction d'onde. Les effets liés au champ S.C.F. et à l'interaction de configuration sont comparés et différenciés.

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Work Supported by the National Science Foundation.     

σ-π separation: Excited H2 as a model system

The low-lying states of H₂ consist of one core () and one valence () electron and afford a direct evaluation of intershell - interaction. After resolution of the electronic energy into only, only, and - parts, it is shown that an electronic change in this model system is due solely to a change in the electrons. Simple Hückel theory is examined. If the molecular core is represented properly, regardless of the wave function the calculated and parameters are in reasonable agreement with the empirical parameters. This agreement appears to be due to a fortuitous cancellation of energy contributions.

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Zusammenfassung Die niedrig liegenden -Zustände des H₂ bestehen aus einem Rumpfelektron und einem Valenzelektron und ermöglichen eine direkte Auswertung der --Wechselwirkung zwischen zwei Schalen. Nach der Zerlegung der elektronischen Energie in -,- und --Anteile wird gezeigt, daß eine elektronische Veränderung in diesem Modellsystem nur auf eine Veränderung des -Elektronenanteils zurückgeht. Die einfache Hückeltheorie wird untersucht. Wenn der Molekülrumpf geeignet dargestellt wird, so sind, unabhängig von der -Wellenfunktion, die berechneten Parameter und in guter Übereinstimmung mit den empirischen Parametern. Diese Übereinstimmung scheint auf eine starke Auslöschung von Energieanteilen zurückzugehen.

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Résumé Les états inférieurs de H₂ consistent en un électron de coeur () et un électron de valence () et fournissent une évaluation directe de l'interaction entre couches -. Après expression de l'énergie électronique en parties , et -, on montre qu'une modification électronique de ce système modèle est due seulement à une modification des électrons . La théorie de Hückel simple est examinée. Si le coeur moléculaire est convenablement représenté, quelle que soit la fonction d'onde , les paramètres at calculés sont en accord raisonnable avec les paramètres empiriques. Cet accord apparaît comme le résultat d'une compensation fortuite de contributions énergétiques.

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Work performed in part under the auspices of the U.S. Atomic Energy Commission.

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Work aided by the U.S. Public Health Service via grant GM 08068.     

Nuclear repulsion effects in molecular bonding

Potential energy curves of a single electron moving in the joint Coulomb field of two fixed nuclei of equal arbitrary charge, Z, have been calculated exactly using a scaling relationship derived in an earlier paper. The resulting potential curves display some interesting features. For Z<1 the 2p antibonding orbital becomes bonding, while the 1s potential well becomes deeper. For larger Z, the 1s orbital eventually becomes antibonding but the potential curve passes through a number of distinct intermediate stages before a purely repulsive potential is reached.