Calculation of retention indices of isoparaffins on different phases

Summry The changes in the retention indices of isoparaffins on phases with different polarities (according to the Rohrschneider-McReynolds system) are examined. It is established that the values of the retention index do not depend on the polarity of the following phases: squalane, normal C₂₄, C₂₈, C₃₀, C₃₂, C₃₄ and C₃₆ paraffins, C₈₇H₁₇₆, the silicones SE-30, OV-1, OV-101, as well as dinonyl phthalate and acetyl tributyl citrate. An empirical equation established peremits the prediction of retention indices of C₆–C₁₀ isoparaffins at different temperatures on all these phases.     

Retention indices of glycerol esters

The retention indices of 27 mono-, di-, and trisubstituted esters of glycerol and C₁–C₆ carboxylic acids were determined on an OV-101 nonpolar phase in the temperature range 110–250°C. The dependence of the retention indices on temperature and the number of carbon atoms in the acid residue was linear for all compounds. The data obtained can be used for identifying glycerol esters in various mixtures and for predicting their thermodynamic properties.     

Gas chromatographic retention indices for C6 alkanols on OV-101 and Carbowax 20M capillary columns

Summary Gas chromatographic retention indices for 16 C₆ alkanols measured on capillary columns coated with OV-101 methylsilicone and Carbowax 20M propylethyleneglycol liquid phases at 80° and 90°C were determined. The respective standard deviation values were 0.5 and 0.8 i.u. The correlation between the retention indices measured on non-polar and polar stationary phases and the boiling points of the alkanols was studied.     

Glass capillary gas chromatography of C1−C4 mononitroalkanes. Pre-calculation of the relative retention

Summary The separation of C₁–C₄ mononitroalkanes on four wall-coated glass open tubular (capillary) columns (liquid phases: OV-101, Ucon-LB-550X, NPGS and Carbowax 20M) was investigated. Retention indices were determined and the influence of the different factors (analysis temperature, method of determining the gas holdup time and the nature of the stationary phases) on their reproducibility were studied. Linear regression equations permit the pre-calculation of the retention indices of C₁–C₄ mononitroalkanes from their properties on all liquid phases studied.     

Gas chromatographic separation of C4−C5 expoxides on a glass capillary colum coated with OV-101 methylsilicone

Summary The separation of C₄−C₅ epoxides on a glass capillary column coated with OV-101 methylsilicone liquid phase was investigated. Retention indices were determined at 70, 80 and 90°C.     

The regularities of the gas-chromatographic behavior of methyl-substitutedN-alkylpiperidines

The gas-chromatographic behavior of 2-, 3-, 4-methyl- and 2,6-dimethylpiperidine bases on glass capillary columns with OV-101/KF and PEG-40M/KF at 110 °C has been studied. The contribution of a methyl group to the total molar free energy of Sorption of nonalkylated piperidine bases depends on its position in the piperidine cycle and is the least for positions 2 and 6. The variation in the retention indices of homologousN-alkylpiperidines (C₁-C₇) is given by a universal type of equation.     

Unified retention indices of alkylbenzenes on OV-101 and SE-30

Summary Gas chromatographic, unified retention-indices of 56 alkylbenzenes up to C₁₅ on dimethylsiloxane OV-101 and SE-30 stationary phases are given. These values agree well with the corresponding experimental values used in the statistical treatment of the experimental data.     

Improved gas chromatographic separation of C6 epoxides

Summary The separation of C₆ epoxides on a fused-silica capillary column coated with Permaphase DMS (dimethylsilicone) was investigated. Retention indices were determined at 50 and 60°C.We demonstrate that this stationary phase provides a better resolving power than OV-101.     

Sorption characteristics ofN-alkylimidazoles under conditions of capillary chromatography

The retention indices forN-n-alkyl (C₁-C₅) substituted imidazoles with Me, Et, Pr, and Bu groups in different positions of the cycle were determined. Two capillary columns with OV-101/KF and PEG-40M/KF were used. The two nitrogen atoms of the imidazole molecule were shown to have different effects on the contributions of the alkyl groups to the retention indices. The maximum and minimum contributions are observed for the substituents at the 5 and 4 positions of the imidazole cycle, respectively. An increase in a size of the C _m H_2m+1 substituent attached to the N(1) atom has a notable effect only on the contributions of the alkyl groups at the 2 and 5 positions. The retention indices values for a homologous series with ann-alkyl group attached to the N or C(2) atom were described by a universal type equation. The obtained equations can be used for predicting the retention indices of new homologs and identification ofN-alkylimidazoles in complex mixtures.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 309–313, February, 1995.     

Mass spectra of some naturally occurring stictane triterpenoids and their trimethylsilyl derivatives

The mass spectra of ten di- and tri-oxygenated stictane triterpenoids and their trimethylsilyl derivatives have been studied in detail. Gas chromatography mass spectrometry of the TMS derivatives on OV-17 and OV-101 columns provided useful separations and identifications of mixtures of stictanes triterpenoids in lichen extracts. The major fragmentations involve ring C, but specific cleavages in rings A, B and E are also observed which allow the substitution pattern of the skeleton to be readily determined. The formation of an intense [M – C₅H₁₁?]⁺ ion for 22α-OTMS stictanes appears specific to their ring E configuration.     

Gas chromatography of homologous esters : XXVIII. Retention increments of aliphatic C1---C18n-alkyl esters of butanoic acid and its monochloro derivatives on SE-30 and OV-351 capillary columns

The retention behaviour of C₁---C₁₈n-alkyl esters of butanoic 2-, 3- and 4-chlorobutanoic acids was examined isothermally at several temperatures on SE-30 and OV-351 capillary columns. Retention increments showing the effects of each position of chlorine substitution are presented. The considerable enhancement of terminal chlorine substitution is discussed together with the corresponding behaviour of the monochloropropanoate esters.     

Behaviour of copper(II) and nickel(II) dialkyldithiocarbamates on polar and non-polar stationary phases

Summary Fifteen Dialkyldithiocarbamate complexes each of copper(II) and Ni(II) have been prepared and the retention times of these complexes have been measured on the non-polar OV-101 phase and the polar NGA and OV-225 phases. The relationship has been studied between the retention characteristics of the complexes and their structure. The lenght of the alkyl substituent, regarded as a steric hindrance, turned out to affect the retention of the complexes on the non-polar phases.

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Verhalten von Kupfer(II)- und Nickel(II)-dialkyldithiocarbamaten auf polaren und unpolaren stationären Phasen

Zusammenfassung Je 15 Dialkyldithiocarbamatkomplexe von Kupfer(II) und Nickel(II) wurden dargestellt und ihre Retentionszeiten auf der unpolaren Phase OV-101 sowie den polaren Phasen NGA und OV-225 gemessen. Die Beziehung zwischen der Retentionscharakteristik der Komplexe und ihrer Struktur wurde untersucht. Es zeigte sich, daß die Länge des Alkylsubstituenten (als sterische Hinderung) die Retention auf der unpolaren Phase beeinträchtigt.

     

Prediction of the chromatographic retention of saturated alcohols on stationary phases of different polarity applying the novel semi-empirical topological index

The novel semi-empirical topological index (I_ET), previously developed by Heinzen and Yunes, was extended to predict the chromatographic retention of saturated alcohols on low polarity stationary phases (OV-1). The predictive ability of I_ET was also verified on stationary phases of different polarity (SE-30, OV-3, OV-7, OV-11, OV-17 and OV-25). Simple linear regressions between the retention indices and the semi-empirical topological index (RI=a+bI_ET) were established for each stationary phase separately, showing good statistical parameters. Statistical analysis showed that the QSRR model used on stationary phases of low polarity (OV-1) has high internal stability and good predictive ability for external groups. The polarity of the SE-30, OV-3, OV-7, OV-11, OV-17 and OV-25 stationary phases, indicated by retention polarity (P_R) given by Tarján et al., is reflected in the ‘a’ (intercept) and ‘b’ (slope) coefficients of the equations obtained for each of these phases. The linear relationship between the ‘a’ coefficient and P_R showed satisfactory statistical quality. Thus, it was possible to generate a single combined model of QSRR, including a parameter that represents the property of the stationary phase P_R. The combined model also has a satisfactory predictive quality, as shown by the plot of calculated versus experimental retention indices for saturated alcohols on six stationary phases of different polarity (r²=0.9956; S.D.=9.54).     

Temperature dependence of the free energy of sorption ofn-alkanes and energy contribution of their methylene groups on columns with fullerene C60

The partial molar free energy, enthalpy, and entropy of sorption of C₁₁−C₂₃ n-alkanes were calculated on the basis of the GC data obtained on the glass capillary column coated with fullerene C₆₀ (Ful-60) as stationary phase. The thermodynamic parameters ofn-alkane sorption on a column with Ful-60 and a fused silica capillary column with polydimethylsiloxane OV-1 were determined and compared. The enthalpy-entropy compensation effect for the sorption ofn-alkanes on Ful-60 and OV-1 was found. A linear dependence of the partial molar free energy ofn-alkane sorption on the temperature of analysis and carbon chain length was found. The free energy contributions of the methylene groups were calculated, and their temperature dependences were studied. The differences in the temperature dependences of the energy contributions of methylene groups ofn-alkanes on Ful-60 and OV-1 were revealed. The entropy contribution is 68–82% of the enthalpy contribution which indicates a substantial role of the number of contacts with Ful-60 in retention ofn-alkanes. The ability of Ful-60 for dispersive interactions is similar to those of nonpolar liquid phases and substantially differs from that for carbon adsorbents. Fullerene columns were shown to be convenient for analysis of highly boiling organic substances in aqueous and organic solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1490–1495, August, 1999.     

Unified retention indices of hydrocarbons on BP-1 dimethylsiloxane stationary phase

Summary Gas chromatographic retention indices for 23 hydrocarbons were determined on BP-1 dimethylsiloxane between 45 and 65°C. From the data measured unified retention indices were calculated. These values agree well with the corresponding experimental values. The values of unified retention indices obtained on BP-1 are compared with those determined on OV-101 and on squalane. The differences between the unified and the experimental retention indices on BP-1, OV-101 and squalane columns are shown.     

The Gas-Chromatographic Behaviour of the Phosphoric Acid n-Alkyl Esters on Silicon Stationary Phases. Reactions on Columns

Abstract

Instability of the trialkylphosphates (RO)₃P(O), with R ? C₂H₁₁ - C₈H₁₇ has been observed when pairs of these esters were analysed on gas-chromatographic columns with silicone stationary phases, e.g., OV-17. New peaks were identified between those corresponding to the initial esters analysed separately. The Kovats retention indices were calculated for these peaks, with n-alkanes, as standards and phosphorus indices with tri-n-alkyl-phosphates as standards. The relationships between the retention indices and the number of the total carbon atoms in the molecules of the alkyl-phosphates was represented for the identification of the new peaks. The new peaks were identified as mixed phosphates with general structure (RO)z(RO)P(O), where R and R are alkyl radicals C₅H₁₁-C₆H₁₇. These phosphates are the results of interchange of alkoxy groups from the esters in the conditions of high temperature (240°C) of the chromatographic colums. The retention data of the esters examined are shown in the table.     

Analysis of reaction by-products in ethylene oligomers by capillary gas chromatography

Summary A gas chromatographic method using temperature-programmed poly-dimethylsiloxane OV-101 and poly(pheny ether) (5 rings) capillary columns was developed to separate and quantify the reaction by-products in ethylene oligomers. It was found that the content of 2-alkyl-1-alkenes, 2-alkenes and n-alkanes in the C₈–C₁₈ -olefin fractions amounts to 29, 10 and 2.6% respectively.     

Structure-retention correlations of hydrocarbons in gas-liquid and gas-solid chromatography. Cycloalkenes and cycloalkadienes

Summary The retention indices of cycloalkenes and cycloalkadienes with C₆–C₁₃ rings are determined by gas-liquid chromatography (GLC) on glass capillary columns coated with OV-1 and Ucon LB 550X and by gas-solid chromatography (GSC) on a microcolumn packed with uncoated graphitized thermal carbon black (GTCB). Structure — retention correlations are derived on using index differences such as H^OV, H^GTCB and ΔI values, considering the differences in the stereochemistry of these compounds. It is shown that the combined application of index increments obtained in GLC and GSC provides more detailed structure informations. The value of the retention index units agree with the most stable conformations of the alicyclic compounds. The high value for the energy equivalent to an index unit (ΔG_I.U.=4.18kJ/mol) confirmes that graphitized thermal carbon black causes much stronger dispersive interactions than any nonpolar liquid phase. Dedicated to Prof. Dr. E. sz. Kováts (Ecola Polytechnique Fédérale de Lausanne) on the occasion of his sixtieth birthday.     

Inequality of temperature increments ofn-alkane homologs as one of the reasons for the nonlinear variation of sorption parameters of substances in temperature-programmed gas chromatography

GC behavior of C₆-C₁₇ n-alkanes has been investigated at different temperatures of isothermal analysis and under temperature programming conditions using two capillary columns coated with OV-101 and OV-351 stationary phases. Temperature increments have been calculated for the homologs and their inequality has been demonstrated for each member of then-alkane series. It was shown that the nonlinear individual temperature variation of the energy of dispersive interaction ofn-alkane homologs with the stationary phase, which was observed under isothermal conditions, may be one of the main reasons for the nonlinear change in sorption parameters ofn-alkanes in temperature-programmed gas chromatography.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 642–645, April, 1994.The present work was carried out with the financial support of the Russian Foundation for Basic Research (Grant 93-03-4969).     

Simultaneous gas chromatographic determination of aliphatic C2−C20 n-carboxylic acids and their methyl esters using SE-30 and OV-351 quartz capillary columns

Summary Simultaneous determination of aliphatic C₂–C₂₀ carboxylic acids and their methyl esters was carried out using SE-30 and OV-351 quartz capillary columns with temperature programming. Complete resolution of all 36 components was achieved. On SE-30 the methyl ester and the corresponding free acid are eluted in turn, whereas on OV-351 acetic acid eluted after methyl octanoate, after which the C_n methyl ester and C_n-6 carboxylic acid (n>9) are eluted one after the other. A non-polar SE-30 column is better for long-chain acids giving sharp peaks without tailing, the analysis time of the mixture being less than 16 minutes. The weight response correction factors for compounds under optimum operating conditions are given.