Formamide as an organic modifier in MEKC with SDS

Area of Science:

• Analytical Chemistry
• Separation Science
• Capillary Electrophoresis

Background:

• Micellar electrokinetic chromatography (MEKC) is a powerful separation technique utilizing micelles to improve the separation of neutral analytes.
• Formamide (FA) is explored as a potential modifier to alter micellar properties and analyte retention in MEKC.
• Understanding the influence of modifiers on micellar behavior and analyte partitioning is crucial for optimizing MEKC separations.

Purpose of the Study:

• To investigate the effect of formamide (FA) as a modifier on analyte retention in micellar electrokinetic chromatography (MEKC) using sodium dodecyl sulfate (SDS).
• To determine how varying concentrations of FA and SDS affect the mobility of alkylphenones and a zwitterionic compound.
• To elucidate the impact of FA on micelle destabilization, critical micelle concentration (CMC), and analyte-micelle interactions.

Main Methods:

• MEKC was performed using a borate buffer (pH 9.23, 50 mM ionic strength) with varying concentrations of formamide (up to 63% w/w) and SDS (10 mM).
• The electrophoretic mobility of alkylphenones and a zwitterionic fluorescent compound was measured as a function of FA and SDS concentrations.
• Partition constants and formation constants for analyte-detergent interactions were derived from mobility-SDS concentration data, including distribution between aqueous and micellar phases.

Main Results:

• Increasing formamide concentration destabilized SDS micelles and increased the critical micelle concentration (CMC).
• At 33% FA or higher, micelles were absent, leading to near-zero retention factors for all analytes.
• Formamide addition generally decreased binding constants, with a pronounced reduction in the partitioning of analyte-monomer adducts into micelles.

Conclusions:

• Formamide acts as a micelle destabilizer in MEKC, significantly altering the separation mechanism by increasing CMC and reducing analyte partitioning.
• The observed changes in micellar properties and binding constants provide insights into analyte-detergent interactions and their dependence on the mobile phase composition.
• These findings highlight the potential of formamide as a modifier to control analyte retention and selectivity in MEKC.