A Dual Column pH Switchable Water Stationary Phase System for Separation Control in Supercritical Fluid...

Area of Science:

• Analytical Chemistry
• Chromatography

Background:

• Supercritical Fluid Chromatography (SFC) is a powerful separation technique.
• Controlling analyte retention in SFC, especially for ionizable compounds, remains a challenge.

Purpose of the Study:

• To introduce a dual-column SFC system with a pH-switchable stationary phase.
• To demonstrate the ability to rapidly modulate analyte retention and improve chromatographic resolution.

Main Methods:

• A dual-column system combining a pH-switchable water stationary phase and a non-polar capillary column was developed.
• Ammonium hydroxide (NH4OH) was used to switch the stationary phase pH between acidic (~pH 3) and basic (~pH 9) conditions.
• The effect of pH switching on ionizable and non-ionizable analytes was investigated.

Main Results:

• The pH switch reproducibly altered the retention time of ionizable analytes by approximately 20-fold, with <1% relative standard deviation.
• Non-ionizable analytes were unaffected by the pH change.
• Demonstrated selectivity reversal (alpha from 0.4 to 1.6) and resolution increase (from 0 to 13).
• Simultaneous determination of multiple acids, bases, and neutral analytes was achieved.

Conclusions:

• The developed dual-column SFC system offers rapid and effective control over analyte retention and selectivity.
• This method simplifies complex mixture analysis by separating target analytes from matrix components.
• The pH-switchable stationary phase provides a versatile tool for optimizing SFC separations.