Tailing, linear chromatography

Fornstedt, T., Zhong, G., and Guiochon, G. Peak tailing and mass transfer kinetics in linear chromatography. J. Chromatogr. A. 1996, 741, 1-12. 

Sources of Band Asymmetry and Tailing in Linear Chromatography. 335... 

Sources of Band A.symmetry and Tailing in Linear Chromatography 181... 

Figure 4 shows calibration curves measured as the peak absorbance at 235 nm. This shows good linearity and high sensitivity for all substances. The detection limit is well below 10 ng for all substances and thus competes favourably with flame ionization detector - GC. The retention times were also measured at all concentrations since it was suspected, due to the apparent tailing, that the chromatography might be non-linear. This did not prove to be so. 

It is often observed, however, that the actual injection profiles are far from the Dirac model, as illustrated in Figure 2.3b, which compares a rectangular pulse injection of 100 fiL (solid line) and the injection profile recorded with a six-port Valeo valve (Houston, TX) fitted with a 100- L loop [42]. The Dirac injection is an acceptable model only if the width of the experimental injection is small compared to the standard deviation of the band profile under linear conditions. Usually, the experimental injection profile has a sharp front followed by a tailing decay (Figure 2.3b). This profile is also typical of those encoxmtered in preparative chromatography, except that they include a concentration plateau lasting for a certain period of time (see Figure 2.3). 

Exchange isotherms measured in dilute solutions are approximately linear that is, the amount of a particular ion held by a resin is directly proportional to the concentration of the ions in the solution in contact with it. At higher concentrations the uptake by the resin begins to fall off, with the result that the isotherm becomes concave to the concentration axis in a manner similar to that depicted in Figure 4.2. Tailing can therefore be expected when the elution technique is used to separate concentrated solutions, otherwise symmetrical peaks, familiar in partition chromatography, will be obtained (Chapter 9). 

Isotherms plot of distribution ratios K, that is, a plot of concentration of the component in the stationary phase versus concentration in the mobile phase. Isotherms represent the relative attraction of a solute for the stationary and mobile phases, the plot is linear for a symmetrical Gaussian peak, non linear isotherms lead to unsymmetrical peaks, e.g. peak fronting and tailing. Langmuir isotherms describe the equilibrium process in adsorption chromatography, Nernst isotherms relate to partition chromatography. 

A. flos-aquae strains they obtained an excellent linearity in their calibration curve in the range, 20-100 ng (on-column) (Harada et al., 1989). Wong and Hindin studied the applicability of LC-UV for the isolation, identification, and quantification of AN. Both normal phase and reversed phase chromatography were examined, but both phases showed poor chromatograms with broad peaks with extensive band tailing (Wong and Hindin, 1982). 

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