The influence of the carrier gas on retention in capillary gas-solid chromatography

In capillary gas-solid chromatography where interactions between solute and carrier gas and adsorption of the solute on the surface of the adsorbent are considered to be imperfect, it has been shown that chromatographic retention is determined largely by adsorption processes. It has been established that correlation relationships k(P₂)=A k(P₁) + B, where k is the retention factor, and A and B are equation constants, was valid for use of different carrier gases P₁ and P₂. Column efficiency could be improved by use of carbon dioxide. The advantages of using carbon dioxide as the carrier gas were investigated.     

Investigation of the role of the carrier gas in capillary gas-solid chromatography

Nonideal interactions of the sorbate and the carrier gas and adsorption of the sorbate on the adsorbent surface in capillary gas-solid chromatography were studied. Chromatographic retention was found to be largely determined by adsorption processes. With respect to the retention coefficients (capacity factors) of a sorbate (k) with different carrier gases (P₁ and P₂), the correlation relationshipk(P₂) =A·k(P₁) +B (A, B are parameters of the equation) is closely obeyed. The advantages of carbon dioxide as the carrier gas were analyzed; the use of carbon dioxide allows the efficiency of the column to be enhanced.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 627–633, March, 1996.     

Influence of the carrier gas on retention factors of gaseous hydrocarbons on polytrimethylsilylpropyne using capillary gas chromatography

The retention factor and height equivalent of a theoretical plate for gaseous hydrocarbons C₁—C₄ were studied on capillary columns with the layer of the new polymeric adsorbent polytrimethylsilylpropyne (PTMSP) as functions of the nature and pressure of the carrier gas. The retention factor k increases in the series helium < nitrogen < carbon dioxide. The k values depend linearly on the average pressure of the carrier gas in a capillary column with the adsorption PTMSP layer.     

Dependence of the relative retention of compounds on the average pressure of helium as a carrier gas in capillary GLC

The dependence of retention factork _i , relative retention time α _i , and retention indexI _i of organic compounds on the average pressure (p _av) of the carrier gas (helium) was studied experimentally using a long narrow-bore capillary column with the SE-30 nonpolar phase at 120°C. The linear dependencesk _i =f(p _av), α _i =φ(p _av), andI _i =φ(p _av) obtained previously were found to be in good agreement with experimental data. Invariant relative retention valuesk _0,i , α _0,i , andI _0,i , which do not depend on the helium pressure, were determined for some organic compounds of various chemical classes. The dependence of the relative retention on the carrier gas pressure needs to be taken into account in precision measurements and in experiments with narrow-bore capillary columns. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 314–316, February, 1998.     

The spread of unicyclic graphs with given size of maximum matchings

The spread s(G) of a graph G is defined as s(G) = max _i,j |λ _i − λ _j |, where the maximum is taken over all pairs of eigenvalues of G. Let U(n,k) denote the set of all unicyclic graphs on n vertices with a maximum matching of cardinality k, and U ^*(n,k) the set of triangle-free graphs in U(n,k). In this paper, we determine the graphs with the largest and second largest spectral radius in U ^*(n,k), and the graph with the largest spread in U(n,k).      

Influence of F and CF3 Groups at the C=C Double Bond on the Structure and Properties of Protonated Forms of Olefin‐Series Compounds: an MP2 ab initio Study

The ab initio MP2 method using the 6–31G^* basis set with full geometry optimization was employed to calculate the protonated fluoroolefin molecules (F)_i(H)_jC=C(F)_k(H)_l (A) and (CF₃)_i(F)_jC=C(CF₃)_k×(F)_l (B), where i + j = k + l = 2. It is shown that a proton is attached to a carbon atom that is linked to fewer fluorine atoms as substituents. In series A, the proton affinity (PA:rpar; passes through a maximum as the number of fluorine atoms in the molecule increases. The highest PA is found for the 1,1difluoroethylene molecule (182.6 kcal/mole). In series B, the PA decreases monotonically, assuming an anomalously low value for the tetra(trifluoromethyl)ethylene molecule (114.7 kcal/mole). The obtained results are compared with Hartree–Fock calculations; the Hartree–Fock method is inadequate for predicting the structures of the carbocations examined.     

Dependence of the relative retention of organic compounds on the nature and pressure of the carrier gas and on the thickness of the PEG-20M film in the capillary column

The effects of the carrier gas nature and pressure on the relative retention values of organic compounds were studied using a series of capillary columns differing in the film thickness of the polar stationary phase (PEG-20M). Relative retention depends linearly on the carrier gas pressure. This dependence becomes more pronounced in the following order of carrier gases: helium < nitrogen < carbon dioxide. The limiting relative retention at a carrier gas pressure approaching zero rather than relative retention values measured experimentally (relative retention time, Kovats retention index,etc.) is an invariant characteristic of a compound subjected to chromatography. For the carrier gases studied, the limiting retention values almost does not depend on the nature of the carrier gas used. The limiting indicating the complex absorption-adsorption nature of these parameters. Dissolution of a carrier gas in the stationary liquid phase has an effect on the relative retention. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2177–2186, December, 1997.     

State‐state transitions for CCl2(X1A1, A1B1, a3B1) radical and collisional quenching of CCl2(A1B1 and a3B1) by O2, N2, NO,N2O,NH3, and various aminated molecules

CCl₂ free radicals were produced by a pulsed dc discharge of CCl₄ in Ar. Ground electronic state CCl₂(X) radicals were electronically excited to the A¹B₁ (0,4,0) vibronic state with an Nd:YAG laser pumped dye laser at 541.52 nm. Experimental quenching data of excited CCl₂(A¹B₁ and a³B₁) by O₂, N₂, NO, N₂O, NH₃, NH(CH₃)₂, NH(C₂H₅)₂, and N(C₂H₅)₃ molecules were obtained by observing the time‐resolved total fluorescence signal of the excited CCl₂ radical in a cell, which showed a superposition of two exponential decay components under the presence of quencher. The quenching rate constants k_A of CCl₂(A) state and k_a of CCl₂(a) state were derived by analyzing the experimental data according to a proposed three‐level model to deal with the CCl₂(X¹A₁, A¹B₁, a³B₁) system. The formation cross sections of complexes of electronically excited CCl₂ radicals with O₂, N₂, NO, N₂O, NH₃, and aminated molecules were calculated by means of a collision‐complex model. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 351–356, 2002     

Reciprocally Unambiguous Conformity Between GC Retention Indices and Boiling Points within Two- and Multidimensional Taxonomic Groups of Organic Compounds

It was shown that reciprocally unambiguous conformity between GC retention indices (at least for the commonly used standard nonpolar polydimethylsiloxane liquid phases) and boiling points of organic compounds is typical not only within one-dimensional taxonomic groups (homologous series and/or groups of congeners), but also within two- and multidimensional taxonomic groups (with simultaneous variations of some structural fragments). In all cases, this conformity is described by three-parameter non-linear equations log RI = a log T_b + b (n₁ + Σ k_i n_i) + c, where n₁ is the serial number of homologue within corresponding series and n_i is the number of other structural fragments in the molecules. The coefficients k_i in this equation reflect the relative alterations of molecular polarizabilities and may be estimated as ratios of refractions k_i = R_D(X)/R_D(CH₂), where X are variable structural fragments within a group of congeners, R_D(CH₂) = 4.647 cm³mol⁻¹. The approach under discussion permits precalculation of the retention indices of any organic compounds with known boiling points. The precision of proposed method of RI precalculation is comparable with the contemporary level of interlaboratory reproducibility of experimental RI determination with standard nonpolar liquid phases (5–10 i.u.).     

Polymer drying. VIII. Molecular interpretations of desorption from polystyrene–liquid systems

The results obtained in time studies that monitored evaporation from liquid-saturated poly(styrene-co-divinylbenzene) to virtual dryness at temperatures ranging from 20 to 80°C confirm those reported earlier for multireplicated time studies at 23 ± 1°C; i.e., when the residual composition (α_t, in sorbed molecules per phenyl group) attains the glassy state composition, the value of α_t thereafter is given by a linear combination of no more than six exponential decay functions. The logarithms of the rate constants (k_i) for decay of these populations at a given temperature decreased linearly with i, the population identification number in the order of decreasing decay rate. The Arrhenius activation energy (ΔE_i) for increase in k_i with temperature was characteristic of the sorbed species, but it was independent of i. The logarithms of the frequency factors (A_i) decreased linearly with i, the slope of which was numerically equal to that observed for the corresponding k_i relationships, signifying that the stepwise decrease of the latter at a given temperature is attributable primarily to a corresponding incremental decrease in entropy. It is suggested that this reflects discrete changes in the molecular structure of polymeric inclusion complexes formed during the transition from the rubbery to the glassy state, as discussed in the text. © 1993 John Wiley & Sons, Inc.     

Reactions of Late First-Row Transition Metal (Fe-Zn) Dichlorides with a PGeP Pincer Germylene

The reactivity of the PGeP germylene 2,2’-bis(di-isopropylphosphanylmethyl)-5,5’-dimethyldipyrromethane-1,1’-diylgermanium(II), Ge(pyrmPiPr₂)₂CMe₂, with late first-row transition metal (Fe-Zn) dichlorides has been investigated. All reactions led to PGeP pincer chloridogermyl complexes. The reactions with FeCl₂ and CoCl₂ afforded paramagnetic square planar complexes of formula [MCl{κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}] (M=Fe, Co). While the iron complex maintained an intermediate spin state (S¹; μ_eff=3.0 μ_B) over the temperature range 50–380 K, the effective magnetic moment of the cobalt complex varied linearly with temperature from 1.9 μ_B at 10 K to 3.6 μ_B at 380 K, indicating a spin crossover behavior that involves S^1/2 (predominant at T<180 K) and S^3/2 (predominant at T>200 K) species. Both cobalt(II) species were detected by electron paramagnetic resonance at T<20 K. The reaction of Ge(pyrmPiPr₂)₂CMe₂ with [NiCl₂(dme)] (dme=dimethoxyethane) gave a square planar nickel(II) complex, [NiCl{κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}], whereas the reaction with CuCl₂ involved a redox process that rendered a mixture of the germanium(IV) compound GeCl₂(pyrmPiPr₂)₂CMe₂ and a binuclear copper(I) complex, [Cu₂{μ-κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}₂], whose metal atoms are in tetrahedral environments. The reaction of the germylene with ZnCl₂ led to the tetrahedral derivative [ZnCl{κ³P,Ge,P-GeCl(pyrmPiPr₂)₂CMe₂}].     

Testing the capability of a polynomial‐modified gaussian model in the description and simulation of chromatographic peaks of amlodipine and its impurity in ion‐interaction chromatography

In this paper, the capability of a polynomial‐modified Gaussian model to relate the peak shape of basic analytes, amlodipine, and its impurity A, with the change of chromatographic conditions was tested. For the accurate simulation of real chromatographic peaks the authors proposed the three‐step procedure based on indirect modeling of peak width at 10% of peak height (W_0.1), individual values of left‐half width (A) and right‐half width (B), number of theoretical plates (N), and tailing factor (Tf). The values of retention factors corresponding to the peak beginning (k_B), peak apex (k_A), peak ending (k_E), and peak heights (H₀) of the analytes were directly modeled. Then, the investigated experimental domain was divided to acquire a grid of appropriate density, which allowed the subsequent calculation of W_0.1, A, B, N, and Tf. On the basis of the predicted results for Tf and N, as well as the defined criteria for the simulation the following conditions were selected: 33% acetonitrile/67% aqueous phase (55 mM perchloric acid, pH 2.2) at 40°C column temperature. Perfect agreement between predicted and experimental values was obtained confirming the ability of polynomial modified Gaussian model and three‐step procedure to successfully simulate the real chromatograms in ion‐interaction chromatography.     

The mechanism of the photochemical reactions of SO2 with isobutane excited at 3130 Å

The mechanism of the reactions of electronically excited SO₂ with isobutane has been studied through the measurement of the initial quantum yields of product formation in 3130 Å irradiated gaseous binary mixtures of SO₂ and isobutane and ternary mixtures of SO₂, isobutane, C₆H₆ or CO₂. Under low-pressure conditions (P < 10 torr) the kinetic treatment of the present data shows that only one singlet and one triplet state, presumably the ¹B₁ and ³B₁ states, are involved in the photoreaction mechanism. The data give k_2a = 8.4 × 10⁹; SO₂(¹B₁) + isobutane → products (2a); k_5a ? k₅ = 8.7 × 10⁸ l./mol·sec; SO₂(³B₁) + isobutane → products (5a) SO₂(³B₁) + isobutane → (SO₂) + isobutane (5b) k_1a/k₁ = 0.145 ± 0.037; SO₂(¹B₁) + SO₂ → SO₂(³B₁) + SO₂ (1a) SO₂(¹B₁) + SO₂ → (2SO₂) (1b) k_2b/k₂ = 0.273 ± 0.018; SO₂(¹B₁) + isobutane → SO₂(³B₁) + isobutane (2b); SO₂(¹B₁) + isobutane → (SO₂) + isobutane (2c) error limits are ± 2 σ. The contribution from the excited SO₂(¹B₁) molecules to the quantum yields of the photolyses of SO₂–isobutane mixtures is not negligible. Under high-pressure conditions (P > 10 torr) the low-pressure mechanism coupled with the saturation effect on the phosphorescence lifetimes of SO₂(³B₁) molecules cannot alone rationalize the quantum yields. The evaluation suggests that some nonradiative intermediate state (X) is involved in the formation of “extra” triplet molecules. This ill-defined state decays largely nonradiatively to SO₂ in experiments at low pressures, X → SO₂ (12). In the presence of C₆H₆ the low-pressure data give k₇ = (8.5 ± 1.8) × 10¹⁰, and the high-pressure data give k₇ = (8.3 ± 0.6) × 10¹⁰ and (9.9 ± 0.9) × 10¹⁰l./mol·sec; SO₂(³B₁) + C₆H₆ → nonradiative products (7). These estimates are in good agreement with values directly measured from low-pressure lifetime studies, (8.1 ± 0.7) × 10¹⁰ and (8.8 ± 0.8) × 10¹⁰l./mol·sec.     

Synthetic aenigmatite analog Na2(Mn5.26Na0.74)Ge6O20: structure and crystal chemical considerations

Disodium hexamanganese(II,III) germanate is the first aenigmatite‐type compound with significant amounts of manganese. Na₂(Mn_5.26Na_0.74)Ge₆O₂₀ is triclinic and contains two different Na positions, six Ge positions and 20 O positions (all with site symmetry 1 on general position 2i of space group P). Five out of the seven M positions are also on general position 2i, while the remaining two have site symmetry (Wyckoff positions 1f and 1c). The structure can be described in terms of two different layers, A and B, stacked along the [011] direction. Layer A contains pyroxene‐like chains and isolated octahedra, while layer B is built up by slabs of edge‐sharing octahedra connected to one another by bands of Na polyhedra. The GeO₄ tetrahedra show slight polyhedral distortion and are among the most regular found so far in germanate compounds. The M sites of layer A are occupied by highly charged (trivalent) cations, while in layer B a central pyroxene‐like zigzag chain can be identified, which contains divalent (or low‐charged) cations. This applies to the aenigmatite‐type compounds in general and to the title compound in particular.     

A study of the bimolecular intersystem crossing reaction induced in the first excited singlet of SO2 by collisions with O2 and other atmospheric gases

The relative intensities of phosphorescence of SO₂(³B₁) molecules have been determined following the optical excitation of SO₂(¹B₁) molecules by a 2662 Å laser pulse. From a kinetic treatment of these measurements, the intersystem crossing ratio, k_2b/(k_1b + k_2b), was determined; SO₂(¹B₁) + M → SO₂(³B₁) + M (2b); SO₂(¹B₁) + M → SO₂ + M (1b). With M = O₂, N₂, Ar, CO₂, and CO, k_2b/(k_1b + k_2b) = 0.030 ± 0.013, 0.034 ± 0.029, 0.025 ± 0.005, 0.052 ± 0.014, and 0.045 ± 0.028, respectively. These data allow a new, more quantitative evaluation of the extent of involvement of the “excess” triplet SO₂ in the 3130 Å-irradiated mixtures of SO₂ and CO at high pressures [5, 6]. The new data are also of direct interest in the determination of the theoretical maximum rates of photooxidation of SO₂ in the sunlight-irratiated atmosphere of the earth.     

Graph-theoretical interpretation of Ugi's concept of the reaction network

The concept of a reaction network, initially suggested by Ugi and coworkers, in the framework of the graph-theoretical model of organic chemistry is elaborated. The reaction network for a pair of isomeric educt molecular (G _E) and product molecular graphs (G _P) is determined as an oriented graph. Its edge, beginning at a graph-vertexG _i –1 and ending at a graph-vertexG _i , corresponds to a feasible transformation (chemical reaction) constrained by a condition of descending chemical distance from the product graphG _P, i.e.CD(G _i –1,G _P) >CD(G _i ,G _P). In the reaction network, an oriented path which begins at G_E and ends atG _P corresponds to the decomposition of the overall transformationG _E G _P into a sequence of elementary transformationsG ₀ =G _E G ₁ G ₂ ... G _i–1 G _i =G _P that may be assigned to intermediates of the overall transformation.     

On the complete set of functions in the Heitler–London method for two-electron problem

It is shown that under certain restrictions the system of determinants φ_i(x₁)φ_k(x₂) ? φ_k(x₁)ψ_i(x₂) constructed from two different sets of orbitals ψ_k and φ_k will be the complete set of functions for antisymmetrical two-electron wave functions if the condition i < k is imposed.     

On the Ordering of a Class of Graphs with Respect to their Matching Numbers

Based on the number of k-matching m(G,k) of a graph G, Gutman and Zhang introduced an order relation of graphs: for graphs G ₁ and G ₂, if m(G ₁,k) ≥ m(G ₂,k) for all k. The order relation has important applications in comparing Hosaya indices and energies of molecular graphs and has been widely studied. Especially, Gutman and Zhang gave complete orders of six classes of graphs with respect to the relation . In this paper, we consider a class of graphs with special structure, which is a generalization of a class of graphs studied by Gutman and Zhang. Some order relations in the class of graphs are given, and the maximum and minimum elements with respect to the order relation are determined. The new results can be applied to order some classes of graphs by their matching numbers.     

Retention of organic compounds in capillary gas chromatography using humid carrier gases

The influence of humid carrier gases (nitrogen and carbon dioxide) on the retention of polar compounds in a capillary column with polypropylcyanophenylsiloxane stationary liquid phase OV-225 was studied. It is noted that when humid carbon dioxide is used as the carrier gas, the retention of primary amines sharply increases. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1129–1131, June, 1999.     

Hosoya polynomials of armchair open‐ended nanotubes

For a connected graph G we denote by d(G,k) the number of vertex pairs at distance k. The Hosoya polynomial of G is H(G,x) = ∑_k≥0 d(G,k)x^k. In this paper, analytical formulae for calculating the polynomials of armchair open‐ended nanotubes are given. Furthermore, the Wiener index, derived from the first derivative of the Hosoya polynomial in x = 1, and the hyper‐Wiener index, from one‐half of the second derivative of the Hosoya polynomial multiplied by x in x = 1, can be calculated. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007