Chromatographic theory plate height

According to chromatographic theory, the reduced plate height is related to the reduced velocity by equation (4.2)... 

HETP = height equivalent to a theoretical plate. It is derived from the plate theory of distillation which is a confusing concept having no basis in fact in the context of modem chromatographic separations. Nevertheless the terms plate number and plate height are still very widely used. 

A high electroosmotic flow through the stationary-phase particles may be created when the appropriate conditions are provided. This pore flow has important consequences for the chromatographic efficiency that may be obtained in CEC. From plate height theories on (pressure-driven) techniques such as perfusion and membrane chromatography, it is known that perfusive transport may strongly enhance the stationary-phase mass transfer kinetics [30-34], It is emphasised... 

In chromatographic theory, a plate is a transverse section of a cross-sectional area equal to the cross-sectional area of the column. The thickness of the plates is called the HETP, or the height equivalent of a theoretical plate. It is derived from the number of plates divided by the length of the column ... 

The van Deemter rate theory identified three major factors that cause band or zone broadening during the chromatographic process the eddy diffusion or the multi-path effect (A-term), longitudinal diffusion or molecular diffusion of the analyte molecules (B-term), and resistance to mass transfer in the stationary phase (C-term). The broadening of a zone was expressed in terms of the plate height, H, and was described as a function of the average linear velocity of the mobile phase, u. 

The rate theory examines the kinetics of exchange that takes place in a chromatographic system and identifies the factors that control band dispersion. The first explicit height equivalent to a theoretical plate (HETP) equation was developed by Van Deemter et al. in 1956 [1] for a packed gas chromatography (GC) column. Van Deemter et al. considered that four spreading processes were responsible for peak dispersion, namely multi-path dispersion, longitudinal diffusion, resistance to mass transfer in the mobile phase, and resistance to mass transfer in the stationary phase. 

The nomenclature also reflects the origin of the concept the distillation theory of gas chromatography. In this concept, a certain length of the chromatographic column was occupied by a theoretical plate. This length was the height equivalent to the theoretical plate. If we divide the column length... 

N column efficiency defined as the number of theoretical plates in the column, i.e., in Plate Theory N describes the number of effective equilibrations of the analyte between mobile and stationary phases N = 4.(Vj/AVj) =4.(tj/Ati) = 5.545.(tf/Atp, where AV and At are the chromatographic peak widths in terms of elution volume and elution time, respectively, and subscripts i and j refer to widths measured at the peak inflection points and at half peak height, respectively. 

Thus, the plate theory supplies an approximate description of the spreading of a component band. If the chromatographic peak width is known, one can calculate the number of theoretical plates, which characterize the column efficiency and hence the equivalent height of a theoretical plate ... 

In classical theory, N was used as a measure of separation power because N increased with greater column length. Height equivalent of a theoretical plate, H, served as a measure of chromatographic efficiency. H in mm or cm is calculated by dividing the column length, I, by the plate number... 

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