Band broadening, chromatographic

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... 

To determine how the height of a theoretical plate can be decreased, it is necessary to understand the experimental factors contributing to the broadening of a solute s chromatographic band. Several theoretical treatments of band broadening have been proposed. We will consider one approach in which the height of a theoretical plate is determined by four contributions multiple paths, longitudinal diffusion, mass transfer in the stationary phase, and mass transfer in the mobile phase. 

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. 

Adsorption-Desorption Kinetics and Chromatographic Band Broadening... 

Experimentally there are two methods of determining the ] extracolumn band broadening of a chromatographic instrument. The linear extrapolation method, discussed above, is relatively straightforward to perform and interpret but rests on the validity.. of equation (5.1) and (5.3). The assu itlon that the individual contributions to the extracolumn variance are independent, may not be true in practice, and it may be necessary to couple some of the individual contributions to obtain the most accurate values for the extracolumn variance [20]. It is assumed in equation (5.3) ... 

For an understanding of band broadening in chromatographic systems, the linear velocity of the mobile phase is more important than the column volumetric flow rate. The mobile phase velocity and flow rate in an open tubular column are simply related by... 

Yau, W. W., Characterizing skewed chromatographic band broadening, Anal. Chem., 49, 395, 1977. 

Injection systems of a capillary gas chromatography should fulfil two essential requirements (i) the injected amount should not overload the column (ii) the width of the injected sample plug should be small compared with band broadening due to the chromatographic separation. Good injection techniques are those which achieve optimum separation efficiency of the column, allow accurate... 

The efficiency of a chromatographic separation can be described by the height equivalent of a theoretical plate (H), where lower values of H correspond to more efficient separations. The Van Deemter equation describes the relationship between H and mobile phase flow velocity (u) as the sum of three major terms, A, B, and C, each of which represents a different contribution to band broadening in a chromatographic column. 

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