Characterization of peak asymmetry with overloaded capillary columns

Abstract A theoretical model for elution peaks (based on the solution of the mass-balance equations with a parabolic expansion of the isotherm equation) is in good agreement with the experimental peak profiles observed in capillary gas chromatography. It depends on four parameters: the peak area, the limiting retention time at zero concentrationm, the global apparent diffusion coefficient, and the peak slant coefficient. The sorption effect, which is a flow-rate increase inside the solute band, has a back-leaning, asymmetrical effect. It is a major contribution to the peak distortions observed in capillary gas chromatography. It is shown that one of the parameters of the theoretical model, the proportionality factor μ O , is characteristic of peak asymmetry and is easily measured from the variation of peak maximum with the amount injected. The asymmetry depends greatly on the magnitude of the second derivative of the isotherm at the origin. It is due to column overloading and is independent of column length and flow-rate. It increases with decreasing column diameter and with decreasing film thickness. This proportionality factor is useful for characterizing the degree of asymmetry of capillary columns, especially for comparing the stationary phases and the coating procedures.