Column efficiency, theoretical plate number characteristic

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 ... 

Primarily the Plate Theory provides the equation for the elution curve of a solute. Such an equation describes the concentration of a solute leaving a column, in terms of the volume of mobile phase that has passed through it. It is from this equation, that the various characteristics of a chromatographic system can be determined using the data that is provided by the chromatogram. The Plate Theory, for example, will provide an equation for the retention volume of a solute, show how the column efficiency can be calculated, determine the maximum volume of charge that can be placed on the column and permit the calculation of the number of theoretical plates required to effect a given separation. 

Efficiency is the measure of the degree of peak dispersion in a particular column as such, it is essentially the characteristic of the column. Efficiency is expressed in the number of theoretical plates (N) calculated as... 

Number of theoretical plates, N A characteristic of a chromatographic column used to describe its efficiency. 

The number of theoretical plates and, thus, the separation efficiency, is determined by the length of the separator column. If two separator columns are used in series, the resulting enhancement of separation efficiency leads to a better resolution between ions with similar retention characteristics, with a corresponding increase in retention times. The separator column length also determines the exchange capacity. An increase of the exchange capacity via elongation of the separator column is recommended in all cases where the ion to be analyzed is present in an excess of another component. 

The number of theoretical plates N, included in Equation (8), is a measure of column efficiency, which can be individually applied to the two columns of a GCxGC set. But in comprehensive GCxGC, the use of two columns having phases with different characteristics results in the redefinition of peak capacity, a 1 D GC efficiency concept. It also results in the introduction of two new concepts related to the separation behaviour, orthogonality and chromatographic structure, which are specific to GCxGC. These three concepts are discussed in Sections 4.2, 4.3, and 4.4, respectively. 

Width of Band. A vital characteristic of a chromatographic column is its efficiency, commonly expressed by its number of theoretical plates, N. N can be calculated from a single band, and is... 

The minimum on the H-u plot (Eq. 5) corresponds to the best separation efficiency, but separations are often performed at a higher-than-optimum flow rate to decrease the run time. The speed vs. efficiency characteristics of various HPLC columns can be optimized using kinetic plots proposed by Poppe. There, the minimum column holdup time, fo, necessary to produce the desired number of theoretical plates, N, can be determined from the diagonal line at the point on the plots of H/u, characterizing the speed of separation vs. N in logarithmic coordinates. The plots are charted for different column types assuming a maximum allowed instrumental pressure, = 40... 

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