Migration of ions in capillary electrochromatography |
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Authors: | Ståhlberg J |
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Institution: | AstraZeneca AB, Tablet Production Sweden, S?dertalje. jan.stahlberg@astrazeneca.com |
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Abstract: | For capillary electrochromatography (CEC) to be a generally used analytical technique the origin of the unusual, and often unwanted, peak shapes, which regularly occur for ionic compounds, must be understood. A mass balance analysis is the most fundamental approach to investigate the origin of non-linear effects during the migration of an eluite. Such an analysis shows that a CEC system composed of ionic compounds has a complex behaviour and that a variety of peak shapes for an eluite ion is expected. In this paper it is shown that the mass balance analysis is rationalised by the introduction of the non-dimensional electrochromatographic migration number omega. This number is defined as the ratio Eu/v0k, where E is the effective electric field strength in the eluite zone, u the mobility of the eluite, v0 the linear velocity of the mobile phase and k the chromatographic capacity factor of the eluite. This work is focussed on the theoretical behaviour of a CEC system for analytical applications, i.e., in the limit of low eluite concentrations. Even under analytical conditions the three-component system studied in this paper shows strong peak broadening when omega has values close to unity. |
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