Columns efficiency and

Using equation (10), the efficiency of any solute peak can be calculated for any column from measurements taken directly from the chromatogram (or, if a computer system is used, from the respective retention times stored on disk). The computer will need to have special software available to identify the peak width and calculate the column efficiency and this software will be in addition to that used for quantitative measurements. Most contemporary computer data acquisition and processing systems contain such software in addition to other chromatography programs. The measurement of column efficiency is a common method for monitoring the quality of the column during use. 

The separation of the critical pair would require a minimum column efficiency and, so, the number of theoretical plated produced by the column must be reported. The... 

Traditionally, column efficiency or plate counts in column chromatography were used to quantify how well a column was performing. This does not tell the entire story for GPC, however, because the ability of a column set to separate peaks is dependent on the molecular weight of the molecules one is trying to separate. We, therefore, chose both column efficiency and a parameter that we simply refer to as D a, where Di is the slope of the relationship between the log of the molecular weight of the narrow molecular weight polystyrene standards and the elution volume, and tris simply the band-broadening parameter (4), i.e., the square root of the peak variance. 

This novel manifestation of the gas chromatographic separation demands that Our fundamental understanding of the GC method-invariably of single-dimensional scope-is challenged as follows concepts of column efficiency and separation are now Supplanted by a need to compare the performances of two columns operating... 

COLUMN EFFICIENCY AND PLATE HEIGHTS IN UNIFIED CHROMATOGRAPHY... 

There have been a few reports of column efficiency and reduced plate height measurements in several unified chromatography techniques. These have been based on the apparent plate height observed at the column outlet. In the notation used by Giddings (32) the apparent plate height, H, is given by the following ... 

It follows that as the variance of the peak is inversely proportional to the number of theoretical plates in the column then the larger the number of theoretical plates, the more narrow the peak and the more efficiently the column has constrained the band dispersion. As a consequence the number of theoretical plates in a column has been given the term Column Efficiency and is used to describe its quality. 

The conceptual idea of a theoretical plate can be used in SEC to measure column efficiency and to compare the performance of packed coluians. For column comparisons it is usually measured with small molecules, such as toluene, acetone or benzyl alcohol, which can explore all of the pores of the packing (K jc - 1). Plate counts measured in this way produce HETP values lower than the actual values measured with monodisperse polymers and proteins. The plate count in this case can be expressed by equation (4.40)... 

Neddermeyer, P. A. and Rogers, L. B., Column efficiency and electrolyte effects of inorganic salts in aqueous gel chromatography, Anal. Chem., 41, 94, 1969. 

For the idealised situation where the operating and equilibrium lines are straight, the overall column efficiency and the Murphree plate efficiency are related by an equation derived by Lewis (1936) ... 

Using O Connell s correlation, estimate the overall column efficiency and the number of real stages required for the separation given in Example 11.5. 

The particle size of a solid support is critical in striking a compromise between column efficiency and speed of separation. Both the multiple path term A and the mass transfer term (CSl of equation (4.46) (p. 89)) are reduced by reducing particle size thus leading to increased efficiency. However, as particle size is reduced, the pressure drop across the column must be increased if a reasonable flow rate is to be maintained. The optimum particle sizes for 1/8 in columns are 80/100 or 100/120 mesh and for 1/4 in columns 40/60 or 60/80 mesh. 

FIGURE 3.13 Dependence on the resolution of two adjacent peaks from the separation selectivity, column efficiency, and capacity factors of peaks. Curves were calculated by keeping values of two parameters constant at the starting value and varying the third parameter. 

LC/MS analyses requiring high resolving power to separate all compounds present in a sample may be optimized as well to increase throughput. Optimizing in the LC dimension utilizes smaller particles as well more radical approaches may involve a change in workflow toward extremely high column efficiencies and peak capacities in contrast to the present common work flow of many individual runs with modified selectivities. 

The strategy employed for choosing a particular chromatographic separation generally entails maximizing the column efficiency and, at... 

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