Column plate height

The A term represents the contribution from eddy diffusion, the B term the contribution from longitudinal diffusion, and the C terms the contributions from mass transfer in the mobile and stationary phases to the total column plate height. By differentiating equation (1.31) with respect to the mobile phase velocity and setting the result equal to zero, the optimum values of mobile phase velocity (u ) and plate height (HETP ) can be obtained. 

The general approach for kinetic optiaization of open i tubular columns has been to adopt the familiar Golay equation T (equation 1.34) and to assuae that the aobile phase can be approximated by an incompressible fluid with ideal gas properties, (44-50). Circumstances that are approximate at best but serve adequately to demonstrate some of the fundamental characteristics of open tubular columns operated at low fluid densities. The column plate height equation can be written in the form given in M equation (6.1)... 

RELATIVE CONTRIBUTION (PERCENTAGE BASIS) OF MASS TRANSFER RESISTANCE IN THE MOBILE AMD STATIONARY PHASE TO COLUMN PLATE HEIGHT FOR A SERIES OF 0.32 mm I.D. OPEN TUBULAR COLUMNS USING UMDECAME AT 130 C AS THE TEST SOLUTE... 

Standards and blanks are the usual controls used in analytical HPLC. Standards are usually interspersed with samples to demonstrate system performance over the course of a batch run. The successful run of standards before beginning analysis demonstrates that the system is suitable to use. In this way, no samples are run until the system is working well. Typically, standards are used to calculate column plate heights, capacity factors, and relative response factors. If day-to-day variability has been established by validation, the chromatographic system can be demonstrated to be within established control limits. One characteristic of good science is that samples... 

As the particle size (dp) decreases, column plate height decreases and the column becomes less permeable. As a result, for small values of dp, a column of some fixed length generates higher plate count i.e., higher... 

As shown by the equations in Section 12.1, column plate height is affected by many parameters, including flow velocity, particle diameter, packing nonuniformity, diffusivities, degree of retention, stationary phase structure, temperature, pressure drop, and pressure. Some of these parameters are interdependent, such as diffusivity and temperature also velocity and pressure drop. Finding a minimum with respect to all of these parameters is an extended task we shall not attempt here. However, we can readily uncover some simple rules for optimizing a few of the major parameters. First we choose flow velocity. 

Fig. 1.3. (A) Three comribulion.s to the column plate height. H. according to ihe van Deemter equation (Eq. (1.10)). (B) Experimental plot of the reduced plate height, h = H /dp as a function of the mobile phase velocity, ii. for a Bio.spher Cis. -5 um. column (13.5 x 0.32 mm i.d.) for toluene in 70% aqueous methanol as the mobile phase.

The contribution of eddy diffusion and other factors to band broadening in liquid chromatography can be quantitatively described by the following equation, which relates the column plate height H to the linear velocity of the solute, ju ... 

The kinetic contributions to zone broadening are evaluated by fitting data for the column plate height, as a function of the mobile-phase velocity, to a mathematical model describing the relationship between the two parameters. Several models have been used in the above experiment, but those by de Ligny and Remijnsee and Knox and Pryde, and developed by Guiochon and Siouffi are most widely used and, at least for a first approximation, allow for comparison and determination of the differences between TLC and column chromatography... 

In chromatography, the van Deemter equation relates the theoretical column-plate height (HETP) to which of the following ... 

Figure 6.12 Comparison between the reduced column plate height vs. reduced mobile phase velocity plots measured for a retained and a nearly unretained solute on a series of spherical (top) and angular (bottom) silica packings. Reproduced with permission from K.K. Unger et ah, J. Chromatogr., 149 (1978) 1 (Figs. 2 and 3).

Equations 18.34,18.35, and 18.36 of the previous subsection still permit the derivation of the optimum mobile phase flow velocity, column plate height, and plate number at iriftnite sample dilution, respectively. The production rate is obtained by combining Eqs. 18.4b, 18.34,18.36, and 18.45. Writing that the differential of the production rate by respect to dp/L is 0 gives the optimum value of this ratio [20] ... 

Using the same relationship as Rnox and Pyper [17] to relate the apparent column plate height and the efficiency imder linear conditions, and to take the finite column efficiency into account, these authors showed also [21] that, under these conditions, the production rate is given by... 

Column plate height, as in chromatography, is defined as H = (f/L, and is, therefore, equal to... 

Figure 1.6. Relationship between the column plate height and mobile phase velocity for a packed column in liquid chromatography.

Relative contribution (%) of resistance to mass transfer in the mobile and stationary phases to the column plate height for undecane at 130°C for a 0.32 mm internal diameter open tubular columns in gas chromatography... 

Inhere H is file sensor column plate height and L is the lengfii of the sensor column. This formula indicates that equilibration volume is determined by the degree of analyte uptake (k ), physical dimensions of the sensor column (Vn, and L), and its chromatognqiltic efficiency (H). 

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