Peak shape improvement of basic analytes in capillary liquid chromatography.

Area of Science:

• Pharmaceutical analysis
• Analytical chemistry
• Chromatography

Background:

• Basic functional groups are common in pharmaceutical active substances.
• Accurate separation of drug substances and impurities is crucial in pharmaceutical research.
• Capillary LC and conventional LC are common separation techniques.

Purpose of the Study:

• To compare the separation efficiency of capillary LC and conventional LC for basic drug substances.
• To investigate the cause of peak deformation in capillary LC separations of basic compounds.
• To identify methods for overcoming the limitations of capillary LC for analyzing basic substances.

Main Methods:

• Comparison of capillary liquid chromatography (LC) and conventional LC.
• Separation of drug substances (levonorgestrel) and potential impurities.
• Analysis of peak shape and separation efficiency.
• Utilized fused silica capillaries and steel tubing for LC columns.
• Investigated the use of deactivated fused silica capillaries.

Main Results:

• Both capillary LC and conventional LC achieved equal separation efficiency for the nonpolar drug levonorgestrel.
• Basic drug substances exhibited significant peak tailing when separated using standard fused silica capillary LC.
• Peak deformation in capillary LC was attributed to interactions between basic analytes and the polar capillary surface.
• This peak tailing was not observed with conventional LC using steel tubing.
• The use of deactivated fused silica capillaries eliminated peak tailing for basic substances.

Conclusions:

• Standard fused silica capillaries in capillary LC can lead to peak tailing for basic pharmaceutical compounds.
• Interactions with the capillary's polar surface are the cause of this peak deformation.
• Deactivated fused silica capillaries provide an effective solution to improve the separation of basic drug substances in capillary LC.