Plate Theory and Extensions - Temperature Changes During the Passage of a Solute Through a Theoretical Plate in Gas Chromatography > Page 78
Despite the possibilities, vacancy chromatography is still rarely used in analytical laboratories although there are a number of applications where it might be useful. Zhukhovitski recommended its use for quality control with a particularly interesting application. Consider a pharmaceutical product that contains a number of ingredients that must be kept in specified proportions. To monitor the drug for quality control purposes, a mobile phase is prepared that contains the components of the product, in the proportions specified, dissolved in the mobile phase at a low concentration suitable for LC analysis. A sample of the drug is dissolved in some pure mobile phase so that the total mass concentration is the same as that of the standards in the mobile phase. The column is brought into equilibrium with the mobile phase containing the standards and the sample injected onto the column. If the product contains the components in the specified proportion, no peaks will appear on the chromatogram, as the sample and mobile phase will have the identical composition. Any component that is in excess in the sample will give a positive peak. Conversely, any component that is present in the sample that is below specifications will give a negative peak. The peak area or peak height, for both positive and negative peaks, will give a quantitative estimation of the amount the component deviates from that specified.
Temperature Changes During the Passage of a Solute Through a Theoretical Plate in Gas Chromatography
Thermal changes resulting from solute interactions with the two phases are definitely second-order effects and, consequently, as such and, as Einstein predicted, their theoretical treatment is more complex. The theoretical treatment of temperature perturbations that result from solute phase interactions, however, provides a good example of the use of the plate concept in a wider sense of chromatography theory.