Sample stacking and sweeping in microemulsion electrokinetic chromatography under pH-suppressed electroosmotic flow

Area of Science:

• Analytical Chemistry
• Separation Science
• Chromatography

Background:

• Microemulsion electrokinetic chromatography (MEKC) is a powerful separation technique.
• Online sample concentration is crucial for improving the sensitivity of MEKC.
• Flavonoids are important bioactive compounds often found in low concentrations.

Purpose of the Study:

• To evaluate two online sample concentration techniques in MEKC: sample stacking and sweeping.
• To introduce a new stacking method: stacking with anion selective electrokinetic injection and a water plug in a reverse-migrating microemulsion (SASIW-RMME).
• To improve the detection limits for analyzing flavonoids.

Main Methods:

• Development and application of the SASIW-RMME technique.
• Use of a specific microemulsion composition: 80 mM sodium dodecyl sulfate, 1.2% ethyl acetate, 0.6% 1-butanol, 10% acetonitrile, and 50 mM phosphoric acid (pH* 1.8).
• Analysis of six flavonoids and a natural product sample (Fructus aurantii Immaturus) using sweeping.

Main Results:

• Significant improvements in detector response were achieved using both stacking and sweeping techniques.
• The limits of detection for the analyzed flavonoids were lowered to the low ng/ml level.
• The SASIW-RMME method demonstrated effectiveness for concentrating and detecting flavonoids.

Conclusions:

• The developed SASIW-RMME technique is effective for online preconcentration in MEKC.
• The method significantly enhances sensitivity, enabling the detection of flavonoids at low ng/ml levels.
• This approach provides a valuable tool for analyzing complex samples like Fructus aurantii Immaturus.