Prediction of the resolution of capillary columns in different conditions of inlet pressure and temperature

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).

Prediction of theoretical plate number in isothermal gas chromatographic analysis on capillary columns

A method for the prediction of the efficiency of gas chromatographic analysis in isothermal conditions by using experimental data of 1-alcohols and n-alkanes measured on capillary columns filled with polar and non-polar stationary phases in isothermal and isobaric conditions is described. The theoretical plate height trend indicates the change of separation efficiency as a function of inlet pressure and column temperature. By evaluating the variation of the diffusion coefficients of the analysed compounds into the mobile and stationary phase it is possible to predict the column efficiency and the number of theoretical plates at any temperature.

Prediction of gas chromatographic peak width in capillary columns at different temperatures, carrier gas flows, column lengths, inside diameters and carbon numbers

Width factor (wf), relative band broadening (br) and retention factor are linearly correlated as ln wf = Inbr + ln k [Chromatographia (2002) 56, 99 -103]. The k and br are thermodynamic and kinetic energy parameters, and expanded to cover volumetric flow of carrier gas, temperature, phase ratio (beta) and carbon number (z). For columns of the same stationary phase and beta value but of different lengths, width at base (wb) can be predicted with the same numerical values of the constants. The average absolute differences between predicted and experimental wb for BP-1 columns of 30, 20 and 10 m are 1.27%, 1.21% and 1.37%, respectively. In predicting Wb of n-alkanes eluted from columns of the same stationary phase but of different ID, only the differences of ln beta are required for adjustment of one of the numerical values. The average absolute differences between Wb(cal) and Wb(exp) values for columns of 0.53, 0.32, 0.22 and 0.15 mm ID are 2.06, 3.67, 3.82 and 3.47%, respectively.

Prediction of retention times and efficiency in linear gradient programmed pressure analysis on capillary columns

A method for the prediction of the retention time and the resolution of chromatographic peaks in different experimental conditions by starting from few experimental data measured in isothermal and isobaric analyses was published previously. In this paper, the same mathematical model was implemented for calculating the retention times and the column efficiency in programmed pressure runs. Some models originated from the Golay equation and reported in the literature are compared, and a new modified equation for the calculation of the peak width at half height is proposed. The procedure for the prediction of the retention time and the peak width at half height at programmed pressure of the carrier gas and different column temperature and linear gradient by using retention data of different compounds obtained in few isobaric runs is described. The prediction of the retention time and the separation efficiency of compounds with different polarity gave good results for the programmed pressure runs with linear gradient. The effect of the variation of the initial parameters of the experimental analyses and of the mathematical model on the accuracy of the prediction has been evaluated.