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. Author manuscript; available in PMC: 2008 Aug 25.
Published in final edited form as: Electrophoresis. 2005 Feb;26(3):633–639. doi: 10.1002/elps.200410061

Figure 2.

Figure 2

Schematic of the pH-mediated acid stacking mechanism showing reverse pressure. (A) A sample in a high-ionic-strength matrix is electrokinetically injected. The field strength drop is primarily across the BGE region of the capillary due to the low resistivity of the sample matrix. (B) A plug of strong acid is next injected electrokinetically. (C) The strong acid titrates the sample region to neutral, creating a zone of high resistivity. (D) As the acid titrates, the analytes are stacked into narrow bands at the boundary of the titrated region and the BGE. The primary field strength drop is now across the titrated zone. (E) Pressure is applied from the outlet of the capillary, pushing the titrated zone out of the capillary, and pushing the analytes near the inlet. The field strength drop is now across the sample zone, and the entire capillary length is available for analyte separation. (F) The separation voltage is applied and the separation proceeds.