Stacking due to ionic transport number mismatch during sample sweeping on microchips.

Area of Science:

• Analytical Chemistry
• Microfluidics
• Electrophoresis

Background:

• Sample stacking can occur in isoconductive buffer systems due to ion transport mismatches.
• Changes in buffer conductivity during electrophoresis can lead to undesirable sample dispersion.
• Hydrophobic dyes are often analyzed using techniques like sweeping with sodium dodecyl sulfate (SDS).

Purpose of the Study:

• To investigate sample stacking in isoconductive buffer systems using fluorescence imaging.
• To examine the sweeping of hydrophobic dyes with SDS on microchips.
• To quantify signal enhancement achieved through sweeping and stacking.

Main Methods:

• Utilized fluorescence imaging on microchips to observe sample stacking.
• Employed isoconductive buffer systems, specifically a sodium borate buffer.
• Analyzed the sweeping of hydrophobic dyes (Rhodamine 560, Rhodamine B, Rhodamine 6G) with sodium dodecyl sulfate (SDS).

Main Results:

• Observed sample stacking in an isoconductive sodium borate buffer system.
• Demonstrated that SDS micelles sweep sample plugs, leading to stacking at the trailing end.
• Achieved significant signal enhancements (86- to 560-fold) for Rhodamine dyes via sweeping and stacking.

Conclusions:

• Sample stacking in isoconductive buffers is a viable method for signal enhancement in microchip electrophoresis.
• The observed stacking effect can be modeled using moving boundary equations.
• Developed a method for analyte trapping and concentration from multiple injections using sweeping/stacking and electric field manipulation.