Chromatographic processes plate height

Electrochromatography was first demonstrated in the open-tubular microfluidic channel coated with octadecylsilane (ODS) as the chromatographic stationary phase. EOF was used as the pumping system within the 5.6-pm-deep and 66-pm-wide channels. Plate heights of 5.0—44.8 pm were achieved for three cou-marin dyes [112]. Open-channel CEC separation was achieved using a stationary phase of octadecyltrimethoxysilane [148], CEC separation of some PAHs has also been carried out on a Pyrex chip with a thin film of C8 stationary phase formed using a sol-gel process [338],... 

As is evident from the preceding discussion, the retention behavior of a polypeptide or protein P- expressed in terms of the capacity factor k is governed by thermodynamic considerations. Peak dispersion, on the other hand, arises from time-dependent kinetic phenomena, which are most conveniently expressed in terms of the reduced plate height he, . When no secondary effects, i.e., when no temperature effects, conformational changes, slow chemical equilibrium, pH effects, etc. occur as part of the chromatographic distribution process, then the resolution Rs, that can be achieved between adjacent components separated under these equilibrium or nearequilibrium conditions can be expressed as... 

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. 

In this chapter, the possible causes of the reduced efficiency in MLC will be surveyed and a remediation path will be proposed and discussed. The chromatographic process is rapidly exposed pointing out the thermodynamics (retention time) and the kinetics (peak efficiency). The differences between a classical hydro-organic reversed mobile phase and a micellar phase are recalled. The kinetics of the chromatographic process can be modeled using the Knox equation that relates the reduced plate height to the... 

Here H is the theoretical plate height, a parameter that characterizes the effectiveness of the chromatographic separation. The smaller the H the more powerful is the separation. A is the Eddy diffusion term (or multipath term), B relates to longitudinal diffusion, C represents the resistance of sorption processes (or kinetic term), and u is the linear flow rate. For a given chromatographic system. A, B, and C are constants, so the relationship between H and u can be plotted as shown in Fig. 6. 

We win now introduce two other quantities frequently used in the literature to analyze this separator (we will see in Section 7.1 that they are also used in analyzing chromatographic and related processes, especially in analytical and preparative chemistry) the plate height Ht or H and the plate number Nt or N, which are related to the separator length Lt by... 

The peak dispersion in chromatography is generally characterized by the theoretical plate height (H) and the number of theoretical plates (N). The treatment of the mass transfer processes and the distribution equilibrium between the mobile and stationary phase in a column lead to equations that link the theoretical plate height as the crucial column performance parameter to the properties of the chromatographic systems, such as the linear velocity of the mobile phase, the viscosity, the diflusion coefficient of analyte, the retention coefficient of analyte, column porosity, etc. 

Time-dominated processes inherently govern chromatography. The horizontal axis of a chromatogram is time (and not energy as in spectroscopy). To describe the quality of a chromatographic system the concepts of the height equivalent to a theoretical plate, HETP or H, and the number of theoretical plates N are used (Equation 4.1) ... 

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. 

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