Migration of ions in capillary electrochromatography

Area of Science:

• Analytical Chemistry
• Separation Science

Background:

• Capillary electrochromatography (CEC) frequently exhibits unusual peak shapes for ionic compounds, hindering its widespread analytical use.
• Understanding the fundamental causes of these peak distortions is essential for advancing CEC as a reliable technique.

Purpose of the Study:

• To investigate the origin of non-linear effects and peak broadening in capillary electrochromatography (CEC) for ionic compounds.
• To rationalize mass balance analysis through the introduction of a new dimensionless parameter.

Main Methods:

• A fundamental mass balance analysis was employed to study the migration of eluite ions in a three-component CEC system.
• The non-dimensional electrochromatographic migration number (omega) was introduced and defined as the ratio of effective electric field strength and eluite mobility to mobile phase linear velocity and chromatographic capacity factor (omega = Eu/v0k).

Main Results:

• Mass balance analysis demonstrates that CEC systems with ionic compounds exhibit complex behavior, leading to diverse peak shapes for eluite ions.
• The electrochromatographic migration number (omega) effectively rationalizes the mass balance analysis.
• Significant peak broadening was observed in the studied three-component system under analytical conditions (low eluite concentrations) when omega values approached unity.

Conclusions:

• The study provides a theoretical framework for understanding peak shape anomalies in CEC.
• The electrochromatographic migration number (omega) is a key parameter for predicting and controlling peak broadening in analytical CEC.
• Further research into the theoretical behavior of CEC systems can lead to improved analytical methodologies.