Nonlinear liquid chromatography

Golshan-Shirazi, S. and Guiochon, G., Comparison between experimental and theoretical band profiles in nonlinear liquid chromatography with a binary mobile phase, Anal. Chem., 61, 1276, 1989. 

There are a number of causes of peak asymmetry in both gas and liquid chromatography, including heat of adsorption, high activity sites on the support or absorbent, and nonlinear adsorption isotherms. Assuming that good quality supports and adsorbents are used, and the column is well thermostatted, the major factor causing peak asymmetry appears to result from nonlinear adsorption isotherms. 

New concepts presented in this edition include monolithic columns, bonded stationary phases, micro-HPLC, two-dimensional comprehensive liquid chromatography, gradient elution mode, and capillary electromigration techniques. The book also discusses LC-MS interfaces, nonlinear chromatography, displacement chromatography of peptides and proteins, field-flow fractionation, retention models for ions, and polymer HPLC. 

With binary and ternary supercritical mixtures as chromatographic mobile phases, solute retention mechanisms are unclear. Polar modifiers produce a nonlinear relationship between the log of solute partition ratios (k ) and the percentage of modifier in the mobile phase. The only form of liquid chromatography (LC) that produces non-linear retention is liquid-solid adsorption chromatography (LSC) where the retention of solutes follows the adsorption isotherm of the polar modifier (6). Recent measurements confirm that extensive adsorption of both carbon dioxide (7,8) and methanol (8,9) occurs from supercritical methanol/carbon dioxide mixtures. Although extensive adsorption of mobile phase components clearly occurs, a classic adsorption mechanism does not appear to describe chromatographic behavior of polar solutes in packed column SFC. 

Forgoes, E. Cserhati, T. Determination of retention behaviour of some non-ionic surfactants on reversed-phase high-performance liquid chromatography supports by spectral mapping in combination with cluster analysis or nonlinear mapping. J. Chromatogr., A 1996, 722, 281-287. 

For the low concentrations used in liquid chromatography, the elution peak is Gaussian in shape and its retention factor is independent of the sample size. When isotherms are nonlinear (convex or concave, as illustrated in Fig. 1), an asymmetric elution peak is obtained and the retention factor measured at the peak apex is dependant on the sample size. 

Sorption Effect A nonlinear effect due to the difference in the partial molar volumes of the component in solution in the mobile phase, and adsorbed on the stationary phase. In liquid chromatography this effect is negligible. It is important in gas chromatography. 

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