Plate height tailing

Studied responses were resolution, " " analysis time, migration time, plate count, tailing factor, tablet content, peak area, peak height, peak width, and peak area/migration time ratio. ... 

The problem that reduction of the plate heights will not considerably improve the peak shapes on MIP phases has perhaps not been recognized immediately when MIP CEC was developed. A recent (2006) review by Ch. Nilsson and S. Nilsson [13] concludes, however So far all verified imprint-based CEC separations showed peak tailing, due to polydispersity of the imprinted receptor sites, resulting in different affinity and poor mass transfer. Although we do not agree with the exact wording (because the isotherm may be nonlinear even if all sites are the same... 

Another problem associated with using the number of theoretical plates (N) as a performance criterion is that there are several equations which can be used to make this calculation, as shown in Figure 1. All of these equations are equivalent for gaussian peaks. However, for tailing peaks, all of the equations are subject to error, some more than others. Therefore, a measure of peak symmetry is required to be able to determine the validity of plate height measurements. 

Fig. 5-14 [63] shows van Deemter plots obtained for columns packed with 5, 10 and 30 p,m oc-tadecylsilica. The smaller the particle the less was the dependence of linear velocity on the theoretical plate height. Chromatograms of aliphatic and aromatic hydrocarbons are shown in Fig. 5-15 [65]. Use of the octadecylsilica in micropacked columns allows improvement of the efficiency of capillary packed columns. No tailing was observed. Application of these sorbents to gas chromatography, especially in packed capillary columns, is, in our opinion, a very promising direction [55, 63-69]. We also think that this type of modified adsorbents can be successfully used in gas adsorption on open capillary columns.

Name Retention Time Area Height K Prime USP Resolution USP Tailing USP Plate Count... 

Because of some peak tailing, the number of theoretical plates was based on peak width at one-half peak height Ns5.S4 he pooled standard deviation (all temperatures) of retention time measurements (dfs34) was t 0.007 minutes. 

The calculation of column theoretical plates by the width at half-peak height is insensitive to peak asymmetry. This is because the influence of tailing usually occurs below that measurement location. The consequence will be an overestimate of the theoretical plates for non-Gaussian peaks. Nine different calculation methods for efficiency have been compared for their sensitivity to peak asymmetry [54]. Besides being influenced by the calculation method, column efficiency is sensitive to temperature, packing type, and linear velocity of the mobile phase. 

Foley and Dorsey (1983) have considered the effect of peak tailing on column efficiency and concluded that measuring peak widths at half height (equation (2.26)) substantially overestimates the number of theoretical plates of a tailed peak. Thus resolution (equations (2.46) and (2.47))... 

A further procedure using five standard deviations (the five sigma method, can also be used as a measure of column efficiency. This measures the width of the peak at 4.4% of peak height (1V4 4) and has the advantage of giving a better indication of undesirable tailing effects (see Figure 1.1). The plate number is calculated from eqn (1.5), but the measured efficiencies will inevitably be lower then the 4 values usually encountered. 

Note that (i) The plate numbers are slightly higher when half-height peak widths are used to calculate them due to peak tailing increasing W( hence comparisons of efficiencies are valid only if the same formula is used throughout. 

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