Theory, chromatography peak shape

J0NSSON, J. A., in Chromatographic Theory and Basic Principles (Jonsson, J. A. ed.), Chapter 3, Dispersion and Peak Shapes in Chromatography (Marcel Dekker, 1987). 

In chromatography the quantitative or qualitative information has to be extracted from the peak-shaped signal, generally superimposed on a background contaminated with noi%. Many, mostly semi-empirical, methods have been developed for relevant information extraction and for reduction of the influence of noise. Both for this purpose and for a quantification of the random error it is necessary to characterize the noise, applying theory, random time functions and stochastic processes. Four main types of statistical functions are used to describe the tosic properties of random data ... 

Jonsson JA (1987) Dispersion and peak shapes in chromatography. In Jonsson JA (ed) Chromatographic science series vol 38, Chromatographic theory and basic principles. Dekker, New York... 

FIGURE 5.5 Mobility spectra for chloride anion as predicted (solid lines) as a function of gate width setting. The corrections for electrostatic repulsion to unite theory and experiment are shown by broken lines. (From Spangler and Collins, Peak shape analysis and plate theory for plasma chromatography, Anal. Chem. 1975. With permission.)... 

Spangler, G. Golhns, G.I., Peak shape analysis and plate theory for plasma chromatography, AwaZ. Chem. 1975,47(403-107). 

Figure 3.2 The elution curve of a single component, plotted as the analyte concentration at the column exit (proportional to the detector response Rj,) as a function of V, the total volume flow of mobile phase that has passed through the column since injection of the analytical sample onto the column. (V is readily converted to time via the volume flow rate U of the mobile phase.) The objective of theories of chromatography is to predict some or all of the features of this elution curve in terms of fundamental physico-chemical properties of the analyte and of the stationary and mobile phases. Note that the Plate Theory addresses the position of the elution peak but does not attempt to account for the peak shape (width etc.). The inflection points occur at 0.6069 of the peak height, where the slope of the curve stops increasing and starts decreasing (to zero at the peak maximum) on the rising portion of the peak, and vice versa for the falling side the distance between these points is double the Gaussian parameter O. Modified from Scott, www.chromatography-online.org, with permission.

In all modes of interactive chromatography, self-association of peptides and proteins can result in significant peak shape distortions, and RPC and HlC are no exception. Such behavior, often described in terms of isodemic interaction theory, is frequently a result of a specific molecular property of the peptide or protein, i.e., the propensity to form amphipathic helices or fibril-like structures or to selfassociate, and can lead to multiple peak zones for an otherwise compositionally homogeneous sample. Participation of such self-association processes can be assessed [127,128,338] by on-line light scattering (LALLS) spectroscopic procedures through an examination of the peak shape response as a function of sample concentration under specified RPC or HlC conditions at a defined pH and temperature. 

The theory of chromatography shows that there should be no noticeable difference between a recorded peak shape and a Gaussian profile so long as the number of theoretical plates of the column exceeds 100 [16]. The difference is small even for 25 plates, and careful experiments would be needed to demonstrate that difference. However, it is common to experience in practice peak profiles that are not truly Gaussian. 

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