S. Le Vent

Calculation of programmed temperature gas chromatography characteristics from isothermal data : I. Theory and computational procedures

Abstract Procedures are described for the calculation of programmed-temperature gas chromatography retention times, elution temperatures, retention indices and two kinds of equivalent temperature from isothermal chromatographic data. These procedures involve the determination of upper integral limits using numerical integration and root-trapping methodology. Computer programs have been written for both single ramp and multiramp/multiplateau temperature programmes.

Calculation of programmed temperature gas chromatography characteristics from isothermal data : II. Predicted retention times and elution temperatures

Abstract Theoretical procedures, described in Part I [ J. Chromatogr. , 405 (1987) 67], for predicting retention indices in programmed temperature gas chromatography from isothermal data are experimentally tested for a number of compounds under a range of experimental conditions. In general, and taking into full consideration random error predictions, agreement is reasonably satisfactory. Also calculated by procedures of Part I are two distinct kinds of equivalent temperature, these being the temperatures of isothermal chromatographic experiments giving the same calculated retention time (a) or index (b) as a corresponding programmed temperature experiment. These temperatures are compared with various simple functions of initial and calculated final temperatures in such an experiment.

Simulation of chromatographic peaks by simple functions

Abstract The quality of bigaussian (BG) and gaussian-lorentzian (GL) simulations of theoretical exponentially modified gaussian (EMG) chromatographic peaks is compared over a range of relaxation time/standard deviation ratios. The GL simulation has superior features above a ratio of about two. A further comparison is made of “best fit” BG, GL and EMG peaks to experimental points for selected gas chromatographic peak types.

Calculation of programmed temperature gas chromatography characteristics from isothermal data: IV. Prediction of peak widths

Two alternative theoretical procedures are described for the calculation of peak widths in programmed temperature gas chromatograms from corresponding isothermal widths. The essential distinction between the procedures for the case of essentially temperature-independent column efficiency is noted. Application to a limited set of isothermal width and retention time data and comparison with experimental programmed temperature results reveals the unsatisfactory nature of one of the procedures. The other method is then applied to a more extensive set of compounds and programmed temperature conditions.

Calculation of programmed temperature gas chromatography characteristics from isothermal data: V. Prediction of peak asymmetries and resolution characteristics

A previously described procedure for the calculation of peak widths in programmed temperature gas chromatograms from corresponding isothermal widths has been adapted to the analogous calculation of peak asymmetries. Comparison with experimental data is satisfactory. Composite predictions of retention times, widths and asymmetries are then used to predict (a) the forms of complete chromatograms comprising close peaks, (b) resolution characteristics of such chromatograms and (c) optimum programmed temperature conditions.

Homologous series methods for determining hold-up parameters in isothermal gas chromatography

In isothermal gas chromatography, analysis of retention parameters for successive members of homologous series forms the basis of several established, related methods for determining corresponding hold-up parameters. These parameters may be times, volumes or volumes per mass of stationary phase, with or without volume correction for gas compression. With full statistical considerations, the present paper compares some of these methods and their extensions. The procedures are applied, through a set of microcomputer programmes, to selected experimental data.

Anomalous inverse absorption features in the far-infrared RAIRS spectra of SnCl4 on thin-film SnO2 surfaces

As part of a study of the chemistry of tin oxide chemical vapor deposition precursors at oxide surfaces, we have utilized the so-called buried metal layer approach to obtain far-IR reflection absorption infrared spectroscopy (RAIRS) spectra for SnCl4 adsorbed at a tin oxide surface supported on a polycrystalline tungsten foil. Two types of surface preparation—namely, sputtering with Ar or O2—have been used to clean the tin oxide surfaces prior to experiment. On O2-sputtered surfaces at 300 K, the spectra are dominated by an inverse-absorption feature in the form of a positive-going band in the spectrum, obtained via the ratio of the sample spectrum to that of the clean surface background. At low temperature, the spectra display both the positive-going inverse-absorption feature and the normal negative-going absorption features common to many RAIRS studies from metallic surfaces. On an Ar-sputtered surface, the inverse absorption band is not observed, but is replaced, at least at 300 K, by an absorption ba...

A Summary of the Properties of Van Der Waals Fluids

The well-known van der Waals equation of state is described in standard textbooks and undergraduate courses in physical chemistry, and in chemical and mechanical engineering. Such descriptions generally outline the origin of terms extra to those found in the perfect gas equation and give typical values of the additional parameters involved. Generally, the various implications for fluids satisfying the equation are not covered to any extent, such coverage being scattered throughout more advanced chemical and engineering literature. The purpose of the present paper is to collect together some of the more important of these. Considered here are the various forms of the equation, vapour pressure implications, the compression factor, thermodynamic aspects, Joule and Joule—Kelvin coefficients and associated inversion phenomena.

What is a Perfect Gas Mixture

The definition of a perfect gas mixture varies substantially within the chemistry textbook literature. A recent International Union of Pure and Applied Chemistry (IUPAC) definition is here criticised as being insufficient to cover properties traditionally associated with such mixtures. Possible supplements to the definition to rectify the deficiency are considered. An alternative definition in molecular terms is shown to be comprehensive. The paper should serve as a summary of the properties of a perfect gas mixture and of essential components of its definition.The definition of a perfect gas mixture varies substantially within the chemistry textbook literature. A recent International Union of Pure and Applied Chemistry (IUPAC) definition is here criticised as being insufficient to cover properties traditionally associated with such mixtures. Possible supplements to the definition to rectify the deficiency are considered. An alternative definition in molecular terms is shown to be comprehensive. The paper should serve as a summary of the properties of a perfect gas mixture and of essential components of its definition.