Use of literature values of temperature programmed retention indexes in qualitative analysis by isothermal gas chromatography

Numerous reports have appeared on the determination of temperature programmed retention indexes in gas chromatography and although chromatographic variables should be completely consistent with published data if such indexes are to be of use, the reproduction of such rigorous parameters is quite difficult. This report presents an approximate method for using published values of temperature programmed retention indexes in isothermal chromatography. In general, the temperature dependence of the isothermal retention indexes of a number of compounds can be expressed as a series of oblique lines on a plot with retention index as the abscissa and temperature as the ordinate; the elution order of the compounds at a given, isothermal, temperature is then indicated by the points at which the compounds' oblique lines cut the horizontal line corresponding to the temperature of interest. In linear temperature programmed chromatography, the horizontal line representing isothermal operation becomes, to a first approximation, a sloping line with a gradient corresponding to the programming rate: this has been verified experimentally and may be valid over a wide range of temperatures. This line can be used to predict isothermal retention indexes for use in qualitative analysis.     

Prediction of programmed temperature retention times on linked capillary columns of different polarity

Systems formed by serial connection of capillary columns of different polarity were studied with methods previously used to predict the behavior of linked capillary columns under isothermal conditions and to obtain programmed temperature gas chromatography (PTGC) retention times of the individual columns starting from isothermal data. The two calculation methods were simultaneously applied in order to predict PTGC retention times of the series system starting from isothermal data obtained on the two individual columns. Experimental retention values measured using different temperature programs on the individual columns and on the series systems were found to agree with those calculated.     

Utilization of Rohrschneider's concept and Tekler equation in linear temperature programmed GC. Precalculation of retention data

Summary An extension of Rohrschneider's concept to the field of the linear temperature programmed gas liquid chromatography, is proposed, which is based on Antoine's equation for the temperature dependence of the reduction index of Takács et al. and Tekler. The new method presented in this paper, applied to retention data of two stationary phases of low polarity, PS-255 and OV-105, gives a new possibility of precalculating retention data.     

Optimization and identification in any kind of multi-step temperature programmed gas chromatography

The theory which predicts the retention time, retention temperature, and peak width for any kind of multi-step TPGC and the principle of optimization has been described. Software for optimization and identification in TPGC has been developed on the basis of this theory. It has also been proven that the relationship between peak width in TPGC and the derived or “invented” retention time is similar to that between peak width and retention time in isothermal processes. The validity of the software has been proved by using it to predict retention temperature, retention time, and peak width for any kind of temperature programming and to predict the optimum temperature program for separation of a multihomolog mixture of industrial alcohols and 15 enantiomeric pairs of amino acids.     

Use of Local Lagrange Interpolation for calculation of retention indices in linear temperature-programmed gas chromatrography

Summary The influence of the isothermal temperature, program rate, initial temperature and flow rate on retention indices was studied. The methods of Kováts, Van Den Dool and Local Lagrange Interpolation are compared. Ten experimental measurements were carried out on a capillary column coated with OV-101 stationary phase.     

Prediction of the separation number of capillary columns in programmed temperature gas chromatographic analysis

The efficiency of capillary columns in programmed temperature analysis can be evaluated by calculation of the separation number (“Trennzahl”). A procedure for the prediction of this parameter at various initial temperatures, carrier gas pressures and heating rates, by using as the starting data the retention times and the peak widths obtained in some isobaric and isothermal runs is described. An equation is proposed that permits to obtain the values of the peak width at half height in any isothermal and linearly programmed temperature gas chromatographic run and therefore to calculate the separation number value. The effect on this parameter of the column polarity was investigated by using polar and non-polar compounds (n-alkanes and 1-alcohols).     

Calculation of retention indices at an assigned temperature from temperature-programmed data

Summary A method is presented for the calculation of retention indices at an assigned temperature from temperature-programmed data. If the retention times at two different program rates for the solutes and the n-alkanes are known, the retention indices at an assigned temperature can be calculated directly.     

Temperature programming elution in capillary supercritical fluid chromatography

Summary Effects of column temperature on the retention behaviour of aromatic hydrocarbons and dialkyl phthalates were investigated in capillary supercritical fluid chromatography (SFC) with carbon dioxide as the mobile phase. Negative temperature programming could partly replace pressure programming. Positive temperature programming was applicable to solutes with proper volatility, in which gas chromatography-like retention mechanism (partition process) was involved.     

A new temperature programmed injection technique for capillary GC: Split mode with cold introduction and temperature programmed vaporization

Summary A new technique of split injection in capillary column Gas Chromatography is evaluated. The sample is introduced in the injector at low temperature and then vaporized by a fast programmed heating. The split is open all the time and the sample amount entering the column is proportional to the preset split ratio. It is demonstrated that no discrimination occurs and that it is possible to inject a very concentrated solution or undiluted sample with a high degree of accuracy and reproducibility in the same injector used for the total sample introduction or solvent — split introduction mode.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Peak broadening in isothermal runs due to large retention gaps in capillary GC?

A simple formula is derived which allows estimation of the band broadening due to longitudinal diffusion in retention gaps for isothermal runs with the column held at the injection temperature. The broadening is strongly dependent on the linear gas velocity in the retention gap. If the internal diameters of the retention gap and the separation column are similar, the retention gap may have a length exceeding 100 m, even if the separation column is only 10 m long. A 0.5 mm I.D. retention gap attached to a 0.3 mm I.D. separation column (of interest for automatic on-column injection) may be several meters long. Retention gaps of 0.3 mm I.D. may be used for on-column injections into separation columns with I.D's. down to about 0.1 mm.     

Phenomenon of dual‐ and single‐retention behaviors of solutes and its validation by computational simulation in linear programmed temperature gas chromatography

The current theory of programmed temperature gas chromatography considers that solutes are focused by the stationary phase at the column head completely and does not explicitly recognize the different effects of initial temperature (T_o) and heating rate (r_T) on the retention time or temperature of a homologue series. In the present study, n‐alkanes, 1‐alkenes, 1‐alkyl alcohols, alkyl benzenes, and fatty acid methyl esters standards were used as model chemicals and were separated on two nonpolar columns, one moderately polar column and one polar column. Effects of T_o and r_T on the retention of nonstationary phase focusing solutes can be explicitly described with isothermal and cubic equation models, respectively. When the solutes were in the stationary phase focusing status, the single‐retention behavior of solutes was observed. It is simple, dependent upon r_T only and can be well described by the cubic equation model that was visualized through four sequential slope analyses. These observed dual‐ and single‐retention behaviors of solutes were validated by various experimental data, physical properties, and computational simulation.     

Simplex optimization of a programmed temperature capillary gas chromatographic separation

The modified simplex algorithm proposed by Nelder and Mead has been used to optimize the separation by temperature programmed capillary GC, of volatile compounds present in alcoholic beverages. An adequate objective function, CRF, based on the separation factor of Kaiser has been used for the optimization process. A factorial design was initially performed to verify the relationship between the several parameters of interest. Following this, the optimization was executed and a surface adjusted within the set of experimental data.     

Prediction of retention values in linear temperature programming of narrow and mega-bore capillary columns

Retention times in linear temperature programmed gas chromatography on narrow bore and megabore capillary columns have been calculated from experimental retention times measured at three isothermal temperatures: an iterative procedure performed by BASIC programs was used to obtain the values of the constants enabling the calculation of the programmed temperature retention times. Different methods of calculation have been compared.     

Determination of thermodynamic characteristics from retention data in GC

Summary Retention data have been measured for model substances of different polarities under isothermal conditions at several temperatures using capillary columns coated with Carbowax-20M and SP-2100 stationary phases. By using the k capacity ratios obtained for various temperatures the thermodynamic characteristics of the partition process were determined. For homologous series linear relationships can be established between thermodynamic characteristics and carbon number. Thermodynamic characteristics can be used both to compare and evaluate column quality and to predict retention indices for different temperatures and linear programmed temperature conditions.Dedicated to Professor J. F. K. Huber on the occasion of his 60th birthday.     

Calculation of retention factors in capillary electrochromatography from chromatographic and electrophoretic data

Retention factors in capillary electrochromatography (CEC) were calculated by means of theoretically derived equations and experimentally determined parameters in microcolumn liquid chromatography and capillary zone electrophoresis. It was found that the retention factor of uncharged components in CEC was about 20% higher than was calculated. The derived equations do not take into account alteration of the nature of the stationary phase or distribution constant by the applied electric field. However, the influence of the electric field on the retention in CEC can be estimated. Individual field contributions could not be determined.     

The temperature dependence of retention indices in gas chromatography

Summary A linear dependence of (T–T₁)/[1(T)–1(T₁)] on temperature (considering the retention index 1(T₁) at temperature T₁ as a standard value) is derived. Both ther retention index at an assigned temperature and the temperature dependence of the retention index can be calculated from retention data measured at two temperature-programing rates.