Capillary Electrophoresis: Applications

Capillary gel electrophoresis uses a porous gel polymer matrix to separate analytes based on size, providing molecular sieving action. It effectively separates macromolecules like proteins, DNA fragments, and oligonucleotides that have similar charges but differ in size. This technique played a significant role in DNA sequencing, particularly in the Human Genome Project.

Capillary zone electrophoresis separates ionic components based on differences in electrophoretic mobility rather than size. It efficiently separates charged species like inorganic ions, organic acids, amines, and large biomolecules such as proteins. This mode has been used to separate proteins, amino acids, and carbohydrates in minimum time, making it a major technique in proteomics.

Micellar electrokinetic chromatography overcomes capillary zone electrophoresis's limitation of not separating neutral species by adding a surfactant like sodium dodecyl sulfate to the buffer solution. The separation mechanism depends on differences in distribution constants between the mobile aqueous phase and the hydrocarbon pseudo-stationary phase. This technique has separated pharmaceutical compounds, vitamins, and explosives.

Capillary isoelectric focusing separates amphiprotic species, such as amino acids and proteins containing weak carboxylic acid and amine groups. A zwitterion does not migrate in an electric field when the solution's pH equals its isoelectric point, making the isoelectric point a key characteristic for separating such molecules. Separations are based on differences in equilibrium properties rather than migration rates.

Capillary electrochromatography uses nonpolar stationary phase-packed capillary tubing to separate neutral species through partitioning between the stationary phase and buffer solution. The separation process is similar to high performance liquid chromatography, yet it does not require high-pressure pumps. Capillary electrochromatography offers superior efficiency and reduced analysis times compared to high performance liquid chromatography.

Capillary isotachophoresis separates cations or anions based on equal velocity migration of all analyte bands. Analyte ions migrate with unique velocities initially, forming adjacent bands that ultimately move at the same velocity. This mode separates either cations or anions but not both simultaneously.

Capillary array electrophoresis operates multiple capillaries in parallel for DNA sequencing applications. DNA is fragmented and labeled with fluorescent dyes, with the sequence determined by the dye color sequence of the eluting fragments. This parallel processing approach significantly accelerates DNA sequencing workflows.