Performance optimization of ultra high-resolution recycling liquid chromatography

Area of Science:

• Chromatography
• Separation Science
• Analytical Chemistry

Background:

• Twin-column recycling separation processes (TCRSP) are employed for challenging separations, but their optimization requires careful consideration of various parameters.
• Efficiency losses due to recycling and inter-column dispersion can negatively impact separation performance.
• Kinetic plots based on ideal TCRSP assumptions provide a framework for optimization.

Purpose of the Study:

• To investigate the optimization of TCRSP for maximum resolution and maximum speed-resolution.
• To identify optimal chromatographic parameters including operation pressure, column length, and inner diameter.
• To demonstrate the method's application to challenging small molecule separations in reversed-phase liquid chromatography (RPLC).

Main Methods:

• Optimization based on kinetic plots assuming ideal TCRSP.
• Examination of operation pressure (3000–12,000 psi), column length (10–25 cm), and column inner diameter (2.1–4.6 mm).
• Experimental validation using commercially available columns for chiral and isotope separations, followed by modifications to reduce inter-column dispersion.

Main Results:

• Highest resolution predicted for 25cm columns with specific particle sizes at different pressures.
• Maximum speed-resolution expected for 10cm columns with specific particle sizes.
• 3.0mm inner diameter columns minimize dispersion effects.
• Optimized columns (3.0x150mm with 2.5µm or 2.7µm particles) demonstrated high performance for challenging separations.
• Replacing standard components with low-dispersion prototypes increased resolution factors by +60% and +80%.

Conclusions:

• The study provides a systematic approach to optimizing TCRSP for both resolution and speed.
• Reducing inter-column dispersion is crucial for achieving significant resolution gains in multi-cycle TCRSP.
• The optimized TCRSP method, particularly with reduced dispersion, effectively enhances the separation of small molecules with low selectivity factors.