Overall Chromatographic System Optimization

Figure 1-9 demonstrates that satisfactory separation could be obtained by optimization of either efficiency or selectivity or both at the same time. Efficiency is essentially the property of the column, but selectivity is the reflection at the nature of analytes and the surface chemistry of the packing material. Combination of these descriptors would allow the characterization of the overall separation power of a particular chromatographic system. 

On the other hand, optimization of the column temperature may significantly improve the overall performance of the chromatographic system. Several studies describe a combination of temperature control with the mobile-phase composition changes and the effect of the combined parameters on reversed-phase separations [10]. 

Chemometric optimization of the chromatographic system consists, in fact, in predicting local maxima in multiparametric space and, then, in further deciding which of these parameters is global with regard to the overall efficiency of a given chromatographic system. 

It is seen from equation (20) that the minimum detectable mass, or mass sensitivity of a chromatographic system, where the column has been designed to have the optimum radius for the detector employed, is directly proportional to the extra column dispersion and the detector concentration sensitivity. It follows that detector dispersion is as important as detector sensitivity in its influence on the overall chromatographic mass sensitivity where the chromatographic system has been optimized with respect to the radius of the column. The effect of extra column dispersion and in particular, detector dispersion on the overall mass sensitivity of the chromatogaphic system is not generally appreciated or completely understood. As the total extra column dispersion is the integral of a variety of sources, the distribution and nature of the various sources of dispersion will now be considered in some detail. 

Overall, the trend is toward increased usage of process gas chromatographs in the future. This is based on the need for plant optimization as well as increased reliability and reduced maintenance of these on-line analyzer systems. Several reviews of this type of analyzer and their manufacturers have been recently published (124-131). 

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