Theoretical Plate Number N

A limit o/T 2 is considered acceptable for most forensic applications. Theoretical Plate Number (N) 

The theoretical plate is a hypothetical measurement of the efficiency of the column. The theoretical plate number should be determined upon first use of the column and the value monitored throughout the column lifetime. Using the last peak in the chromatogram, the measurement of N should be determined it can be calculated using the following equation  

System suitability testing is essential for the assurance of quality performance of the chromatographic system. The amount of testing required will depend on the purpose of the test method...each method submitted for validation should include an appropriate number of system suitability tests defining the necessary characteristics of that system. 

Some forensic laboratories will rim what is known as a QC (quality control) sample ahead of the analytical sequence to assess whether all of the system suitability criteria are met. The QC sample is a simulated sample of known concentration and is prepared independently by one or several members of staff within the laboratory. Generally, the QC sample is run and assessed against the system suitabiUty criteria before the start of the analytical sequence and again at the end. The concentration of the sample is calculated and assessed against the true value. A Umit is set and this must be met in order for the data to be considered vaUd. 

---

FIGURE 14.1 Determination of the theoretical plate number N by the half-height method. 

The theoretical plate number N of peak B can be calculated from the chromatogram given in Figure 1.3 by the following equation ... 

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

Theoretical plate number, n. Number defining the efficiency of the column or sharpness of peaks. 

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... 

System suitability specifications and tests, Capacity factor (k ), Preci-sion/injector repeatability (RSD), Relative retention (a), Resolution (Rs),Tailing factor (T),Theoretical plate number (N)... 

Table 1(a). Variation of Theoretical Plate Number N, and Resolution, Rs, with Variation in Methanol Concentration... 

The efficiency remains high even with high concentrations of methanol. With acetonitrile as the modifier, the efficiency was significantly reduced as the concentration of the modifier was increased. For this study the theoretical plate number (N) was estimated using the equation of Foley and Dorsey (5M. 

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 ... 

The driving force behind the application of CEC so far has been theoretical plate number, N. The classic separation [64] of tipredane diastereoisomers by... 

For practical purposes, several terms need to be defined. These are capacity factor (k ), theoretical plate number (N), height equivalent to one theoretical plate (F1ETP), selectivity (a) and peak asymmetry (b/a). As will be discussed later in specific examples (Sects. 9.2.4 and 9.2.5), these parameters are of crucial importance in monitoring and maintaining HPLC column efficiency. 

Theoretical Plate Number (N) and Height Equivalent to One Theoretical Plate (HETP)... 

The efficiency of separation, expressed as theoretical plate number, N, is calculated as follows ... 

This parameter is very useful in chromatography for the characterization of peak broadening per unit length of the column. In addition to H, the peak broadening characterization in a column can be done using the theoretical plate number n. For a column of length L, n is defined as... 

Rel. (17a) indicates that n is proportional to the column length L and inversely proportional to H. The theoretical plate number n can be expressed as a function of length using a simple substitution of rel. (16) in rel. (17a) ... 

Chromatographic resolution of any two components in a mixture is dependent on three factors (1) the overall efficiency of the chromatographic system, as described by the number of theoretical plates N, (2) the inherent selectivity of the system, described by the selectivity factor a, and (3) the degree of retention of each of the components, described by their capacity factors k. For two peaks having approximately equal widths, capacity factors of ki and 2, and a mean theoretical plate number N, the following quantitative... 

Generally, the column efficiency is expressed in terms of the theoretical plate number N or the height equivalent to a theoretical plate, H ... 

The number of these theoretical transverse slices of column is known as the theoretical plate number (N) and reflects the number of times a solute partitions between the two phases. is a measure of the efficiency of the column and will determine how broad the chromatogram peaks will be. A column with a high number of theoretical plates will be efficient and will produce narrow peaks. 

From the input values of F, the theoretical plate number, N is calculated by the relationship- approximately modified for thecolumn used (experimentally determined), though generally N is a function of linear velocity of the mobile phase. 

Joule Heating in Electrokinetic Flow Theoretical Models, Fig. 4 Comparison of the theoretical plate numbers, N = Lo/H, between the analytical solution (lines) and the previous experiment (symbols). The solid line is determined from Eq. 46, while the dashed line accounts for 40 % of the plate numbers in the solid line (Reprinted from [7])... 

If the entire column length L is considered as being divided into sections of the length H5 (in the following referred to simply as H), we obtain the theoretical plate number N ... 

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

The theoretical plate number N h required to achieve a resolution of 1.5 is calculated from Equation 2.2 as ... 

A good-quality column is estimated in terms of column efficiency which is measured by the theoretical plate number N of the column or the height equiva-... 

In a chromatographic process, a solute is equilibrated many times between the mobile and stationary phases during passage through the column. Each equilibration is equivalent to one equilibrium stage or one theoretical plate. Though in SEC, the concept of the so-called stationary phase, as in other chromatographic separation modes, is not definitive, the theoretical plate number N derived from the plate theory is still used as a measure of column efficiency. 

Analyte zones in CE are generally narrower than in conventional ion chromatography. Inefficient mass transfer of analytes between Uquid and solid phases, together with a curved eluent flow profile due to pumping, are major sources of zone broadening in packed columns, but these are avoided in CE. Jorgenson and Lukacs [1] showed that the theoretical plate number, N, in CE can be expressed by the following equation ... 

Enhancement of thin-layer performance is basically understood as elevation of the theoretical plate number N for a given type of chromatographic plate. The quantity N was defined in Section III.A... 

---