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An Analogue Column Model for Nonlinear Isotherms: The Test Tube Model
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Abstract
Asymmetric chromatographic peaks, "tailing" and "fronting", have been explained well by the convex and concave isotherms, respectively. However, it is not always easy for students to come to an instantaneous understanding of the theoretical basis of the peaks. We devised an analogue column model for non-linear isotherms. We have named this model the "test tube model" (TT-model). In the TT-model for convex isotherm, one theoretical plate is represented by a pair of test tube and trumpet-shaped vessels, representing the stationary and mobile phases, respectively. The trumpet-shaped vessel is designed to represent a Langmuir isotherm by pairing it with the test tube. Solute is represented by "water". Therefore, the volume of water denotes the amount of solute. At equilibrium, water is partitioned between two vessels according to the isotherm. This partition is accomplished by making the water levels in the two vessels the same. Alternate repetitions of the equilibrations and the transfer of the series of mobile phases to the next plates transfer the solutes. In this process, because the center of the band moves faster than the edges, the chromatograph exhibits "tailing". The exchange of the two kinds of vessels produces the TT-model for concave isotherm. These explanations based on the TT-models are much more understandable that other explanations.
Keywords (Audience):
Second-Year UndergraduateKeywords (Domain):
Analytical ChemistryKeywords (Subject):
ChromatographyTools
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History
- Received: August 03, 2009
ACS
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