Chromatographic peak broadening

From an analytical perspective, the presence of droplets can also lead to apparent chromatographic peak broadening and a loss of resolution and analytical performance. 

Some of the methods for measuring molecular diffusion coefficients, together with a few recent references, are (a) diaphragm cell [60,61] (b) boundary layer interferometry [59] (c) shearing plate interferometry [58] (d) chromatographic peak broadening [60] (e) nuclear magnetic resonance and electron spin resonance [62, 63] (f) electrolyte conductance [64] (g) isotopic tracers [65] and (h) laminar jets [66]. 

The concept that a rate theory is responsible for contributions to chromatographic peak broadening were first provided by van Deemter, Klinkenberg, and Zuiderweg. The random walk is the simplest molecular model and is due to Giddings (18). 

Dynamic effacts. Besides the thermodynamically driven selectivity, the resolution of the chromatographic system depends also on dynamic (kinetic) factors that determine the efficiency of separation. These factors cause the broadening of the chromatographic peaks so that even peaks fi om individual compoimds such as proteins have a finite width. For polydisperse polymers this chromatographic peak broadening (or bandspreading) is usually hidden by the overall polymer distribution, but still can produce erroneous results if no correction has been made to compensate for this effect. 

The chromatographic peak-broadening technique, as applied to porous solids, was put forward by Davis and Scott [41] and further developed by Schneider and Smith [42]. Analysis of the experimental results is somewhat easier if the gas component injected into the column is not adsorbed on the solid. Because several pellets are used in the column, no seals are needed... 

Assuming a Gaussian profile, the extent of band broadening is measured by the variance or standard deviation of a chromatographic peak. The height of a theoretical plate is defined as the variance per unit length of the column... 

The peak broadening measured for a plate number characterization is the sum of the variances a) for the column and the chromatographic equipment used ... 

Because the polydispersity of the polymer is reflected in the width of the chromatographic peak, we require that the column band broadening contribution to the peak width be minor compared to that from the polymer itself. This criterion cannot always be met. 

Based on the previous analysis of the different transport phenomena, which determine the overall mass transport rate, the structure of the solid phase matrix is of extreme importance. In the case of any chromatographic process, the different diffusion restrictions increase the time required for separation, since any increase of the flow rate of the mobile phase leads to an increase of the peak broadening [12]. Thus, the improvement of the existing chromatographic separation media (column packing of porous particles) and hence the speed of the separation should enable the following tasks ... 

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