Theoretical plates, effective number

Effective theoretical plate number (Aeff), 4, 100 Eluent, 89 Enthalpy, 117, 128 Entropy, 128... 

Effective theoretical plate number. N eff " number relating to column performance when resolution is taken into account. 

A somewhat more realistic measure of the separation efficiency of a column is the effective theoretical plate number N pp ... 

Theoretical plate number N and effective theoretical plate number may then be calculated for both the discrete- and continuous-flow models. A number of chromatographic systems from the literature were examined by Fritz and Scott. In all cases they demonshated the applicability of the actual data to their system. 

FIGURE 4,14 Example of isothermal gas chromatogram simulation. The Analysis tab (shown) displays the elution conditions plus the retention times, peak widths, effective theoretical plate numbers, and resolution for the two peaks flanking the cursor. Program GC-SOS V 5.1 (ChemSW, Inc., North Fairfield, CA). 

The efficiency of an open tubular column can be measured in several ways the most widely used methods are the number of theoretical plates (n), the nu3aber of effective theoretical plates (N), the height equivalent to a theoretical plate (HETP) or effective plate, the coating efficiency and the separation number (SM). No single method is ideal, standardization is lacking and... 

The recycle elution method can be applied to mixtures of very similar compounds that cannot be fully separated by a single pass through the column. This method makes more effective use of a column. The effluent from the column is repeatedly re-passed through the same column. The number of cycles multiplies the total theoretical plate number of the column if the system is... 

If the correctly sized flow cell and connecting tubing are not used, the high efficiency of a column or high theoretical plate number columns cannot be effectively used. The detector cell volume contributes hold-up volume. The larger is the cell volume, the greater the peak broadening. The cell volume... 

The highest theoretical plate number was obtained with 400 ig/mL chloride and 400 j,g/mL of heptanesulfonate. However, when looking at the peak area, we obtained an RSD value of 11.74%, which indicated that stacking and de-stacking only had a minimal effect. Further development was performed without searching for tITP stacking (Figure 22). 

M mass of solute to be separated N number of effective theoretical plates P pressure Q flow rate R resolution S peak capacity Sm specific heat of mobile phase Ss specific heat of adsorbent Sg specific heat of detector cell walls V volume in conventional units Vo system dead volume Vr retention volume V r corrected retention volume Vm volume of mobile phase in the column Vs volume of stationary phase in the column Ve extra column volume... 

Apart from the above-discussed parameters for HPLC optimization of chiral resolution on antibiotic CSPs, some other HPLC conditions may be controlled to improve chiral resolution on these CSPs. The effect of the concentrations of antibiotics (on stationary phase) on enantioresolution varied depending on the type of racemates. The effect of the concentrations of teicoplanin has been studied on the retention (k), enantioselectivity (a), resolution (Rs), and theoretical plate number (N) for five racemates [21]. An increase in the concentration of teicoplanin resulted in an increase of a and Rs values. The most surprising fact is that the theoretical plate number (N) increases with the increase in the concentration of teicoplanin. It may be the result of the resistance of mass transfer resulting from analyte interaction with free silanol and/or the linkage chains (antibiotics linked with silica gel). This would tend to trap an analyte between the silica surface and the bulky chiral selector adhered to it. This is somewhat... 

TABLE 3.5 Effects of Reservoir Levels on Migration Time, Theoretical Plate Numbers, Resolutions, and Peak Heights of Rhodaminel23 and Fluorescein in NLC ... 

In capillary gel electrophoresis, one of the major contributors to band broadening, besides the injection and detection extra-column effects, is the longitudinal diffusion of the solute molecules in the capillary tube [14], The theoretical plate number (N) is characteristic of column efficiency ... 

In addition to the theoretical plate number, an effective plate number N is defined by substituting tp in rel. (17c) with tp. The formula for N will be... 

Rel. (18) shows how N depends on chromatographic retention time tp, and since tp is compound related (index i" omitted), it also shows that N (as well as n) are compound dependent. Both rel. (17c) and (18) can be used to measure the theoretical plate number or effective plate number based on experimental data obtained with a given column. This measurement is useful in practice to select columns (higher n gives lower peak broadening) and also to assess the loss in performance of a column after a certain period of usage. 

While extremely large numbers of theoretical plates are possible with larger diameter columns (22, 23), calculations from chromatographic theory of the Internal diameters and column lengths necessary to achieve relatively high efficiencies in reasonable analysis times Indicate that column diameters of 50 to 100 ym l.d. are necessary for high-resolution SFC (23). For example, more than 10 effective theoretical plates are possible In less than two hours on 30-m long columns of 50 ym l.d. 

Presented in Table I are the dimensions and properties of the several columns prepared in this work. The internal diameter was varied as shown from 0.278 mm to 0.0345 mm, while the stationary-phase film thickness was held constant for all but the last of the columns. Thus, the phase ratio (V] /Vc) decreases on passing from column 1 to 6 over the range 231.5 to 54.25. The solute capacity factors increase accordingly from 6.83 to 29.47. The number of theoretical plates per meter leng N/m for all columns except the first is therefore very nearly equal to the number of effective theoretical plates per meter, since the capacity factors are close to or exceed 10. 

We begin in Chapter 2 with a discussion of the chromatographic process, developing the separate concepts of (1) equilibrium distribution of sample between adsorbent and solvent (or gas) and (2) bed efficiency or theoretical plate number. These two factors are then related in a general way to the problem of separation, and the various techniques of adsorption chromatography are introduced in terms of the different separation problems they are intended to solve. Chapter 3 provides a general discussion of adsorption, emphasizing those fundamental concepts which will be necessary in the discussions of later chapters. The effect of sample size on separation is treated in Chapter 4, particularly the factors which affect isotherm linearity. Chapter 5 provides a complete treatment of bed efficiency in liquid-solid systems. The distribution of sample... 

Effective theoretical plates N ff, the effective or true number of separation steps in a column, takes into account the column dead time in the calculation of column efficiency (see column efficiency). 

Number of theoretical plates N, refers to the number of separation steps in a column, is used to describe the efficiency of a column for a given separation and is calculated using observed retention times see column efficiency and effective theoretical plates. 

A eff Number of effective theoretical plates, effective column efficiency... 

Owing to high theoretical plate numbers, CE makes it possible to observe even very weak (enantio) selective effects in intermolecular interactions that are not detectable using other techniques. This important advantage of CE is not yet effectively exploited for studies of non-covalent intermolecular interactions. 

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