Gianrico Castello

Retention index systems: alternatives to the n-alkanes as calibration standards

The retention index systems based on homologous series or selected compounds differing from the n-alkanes series proposed by Kovats are reviewed and discussed. The reference series proposed for the identification of various kinds of organic compounds, on polar and non-polar columns and with universal or specific detectors, are described. Reference systems proposed for the identification of polyaromatic compounds and of polychlorobiphenyls are also compared.

A method for the identification of branched-chain paraffins by calculation of their retention index values on the basis of molecular structure and physical properties☆

Abstract The retention times of branched-chain paraffins were shown to depend on their physical properties, especially molecular volume, when non-polar phases were used for their separation. As the molecular volume depends strongly on structure, the calculation of additive terms, which are characteristic of every structural group in a molecule, can permit the theoretical calculation of the retention indices of any branched isomer. The additive terms can be calculated both by solving a system of equations and by comparison of the retention indices of selected compounds. The general application of the method to retention data taken from the literature is also possible.

Fast and accurate method for the automatic prediction of programmed-temperature retention times

Abstract Sic calculation methods for the prediction of the retention times in programmed-temperature gas chromatography by starting from isothermal data were applied to capillary column analysis. The minimum number of isothermal runs necessary to obtain accurate results was evaluated. The application of the various methods and the accuracy of the prediction are discussed. A quadratic interpolation method which requires only three isothermal retention values as the starting data was found suitable and easily applied to computer programs.

Analysis of polycyclic aromatic hydrocarbons with an ion-trap mass detector and comparison with other gas chromatographic and high- performance liquid chromatographic techniques

Abstract Some polycyclic aromatic hydrocarbons with a wide range of molecular masses were analysed by high-resolution gas chromatography using an ion-trap mass detector and a flame ionization detector. The sensitivity limits and the possibility of automatic identification through library search were evaluated. The results were compared with those obtained using other analytical techniques: mass spectrometry with a quadrupole analyser and high-performance liquid chromatography with a diode-array UV detector and fluorimetry. The relative sensitivity and the minimum amounts detectable with the various techniques were determined.

Automatic prediction of retention times in multi-linear programmed temperature analyses

A method for the prediction of retention times of compounds analysed during programmed-temperature gas chromatography with capillary columns is described, which employs an explicit equation for the calculation of the gas hold-up time. The method can be applied to analyses carried out with different temperature profiles: constant linear programming rate, initial and final isothermal tract, different temperature gradients in the same analysis. The effect of the various parameters of the analysis on the accuracy of the predicted values was investigated.

Comparison of different methods for the prediction of retention times in programmed-temperature gas chromatography

Four calculation methods that can be easily applied by simple BASIC programming on personal computers were compared for the prediction of the retention times of various substances during linear temperature programming with and without an initial isothermal period on polar and non-polar capillary columns. The methods are based on curve-fitting techniques or a numeric iterative integration approach (Simpson and trapezoid methods). The comparison with experimental data obtained in various programmed-temperature analyses showed that all the tested methods permit the prediction of the retention times. The computation times and deviations of the results are compared.

Sensitivity and linearity of headspace and liquid—liquid extraction techniques for gas chromatographic analysis of halocarbons in water

Abstract The headspace and the liquid—liquid extraction methods for the analysis of trihalomethanes and other halocarbons in water were compared by using mixedcolumns gas chromatography. The sensitivity and linearity of the nickel-63 asymmetric type electron-capture detector were evaluated for CH2Cl2, CHCl3, CCl4, ChCl2Br, CHClBr2, CHBr3, CHCl2CH3, CH2ClCH2Cl, CCl3CH3, CHClCCl2 and CCl2CCl2, using the two extraction methods. In both instances, the linearity extends over several orders of magnitude, thus simplifying the use of calibration techniques for the quantitative analysis and facilitating the use of intergrators and data systems.

Retention models for programmed gas chromatography

The models proposed by many authors for the prediction of retention times and temperatures, peak widths, retention indices and separation numbers in programmed temperature and pressure gas chromatography by starting from preliminary measurements of the retention in isothermal and isobaric conditions are reviewed. Several articles showing the correlation between retention data and thermodynamic parameters and the determination of the optimum programming rate are reported. The columns of different polarity used for the experimental measurement and the main equations, mathematical models and calculation procedures are listed. An empirical approach was used in the early models, followed by the application of thermodynamic considerations, iterative calculation procedures and statistical methods, based on increased computing power now available. Multiple column arrangements, simultaneous temperature and pressure programming, applications of two-dimensional and fast chromatography are summarised.

The gas chromatography of alkyl iodides

Abstract Gas chromatographic separation and identification of several alkyl iodides has been accomplished using glass columns filled with tricresyl phosphate on DMCS treated Chromosorb W. Detection by an electron capture detector (E.C.D.) permitted quantitative determination of about 10−12 grams of iodides in the presence of a large excess of hydrocarbons. Absolute and relative retention times, retention indices and sensitivities to E.C.D. were determined. The retention indices relative to n-alkanes and those relative to 1-iodoalkanes were calculated and correlated. The homologous series of 1-iodoalkanes may be suitable as a reference for the calculation of retention indices of E.C.D. sensitive substances.

Effect of temperature on the polarity of some stationary phases for gas chromatography

Abstract The behaviour of the polarity of some stationary phases as a function of temperature was investigated by using gas-liquid packed columns, open-tubular bonded-phase and carbon and graphite layer capillary columns modified with different percentages of polar liquid phases. The change in polarity of gas chromatographic columns packed with twenty different liquid phases and of nine capillary columns as a function of temperature was measured by using as a polarity indicator the difference in apparent carbon number of linear alkanes and alcohols with the same retention time, ΔC. Some phases were found to have a constant ΔC value over a wide temperature range, whereas other phases change their behaviour and can therefore cause an inversion of the elution order of polar and non-polar compounds at different temperature or during temperature programmed analysis.