Capillary Electrophoresis

Capillary electrophoresis separates ions and charged species by their migration in an electric field within a narrow buffer-filled capillary.

Definition

Capillary electrophoresis is a separation technique in which analytes migrate through a buffer-filled capillary under an applied electric field, separating according to their electrophoretic mobility superimposed on electroosmotic flow.

Scope

This topic covers electrically driven separations performed in fused-silica capillaries: capillary zone electrophoresis and related modes, the role of electroosmotic flow, on-capillary detection, and the high efficiencies these methods achieve. It treats separation based on charge-to-size ratio rather than phase partitioning and its application to ions, biomolecules, and chiral analytes.

Core questions

• How do electrophoretic mobility and electroosmotic flow combine to determine migration time?
• Why does capillary electrophoresis achieve such high separation efficiency?
• What detection schemes are compatible with the small dimensions of a capillary?
• Which analyte classes are best suited to electrophoretic rather than chromatographic separation?

Key theories

Electrophoretic migration and electroosmotic flow

Each charged analyte moves at a velocity set by its electrophoretic mobility, while the whole buffer is swept toward one electrode by electroosmotic flow arising from the charged capillary wall; the sum of these velocities determines migration time and, because the flow is nearly flat rather than parabolic, yields very high efficiency.

Mechanisms

A narrow fused-silica capillary is filled with a buffer and a high voltage is applied across it. The ionized silanol groups on the wall generate an electroosmotic flow that carries the bulk solution past the detector, while each analyte's own electrophoretic mobility adds or subtracts from that motion. Analytes therefore reach the detection point at times governed by their charge-to-size ratio, and the flat flow profile produces extremely narrow zones and high plate counts.

Clinical relevance

Capillary electrophoresis is widely used for nucleic-acid separations including DNA sequencing and fragment analysis, protein and peptide analysis, clinical determination of serum proteins and ions, pharmaceutical and chiral analysis, and small-volume samples where its minimal consumption is advantageous.

History

Electrophoresis as an analytical technique was established by Arne Tiselius in the 1930s. Jorgenson and Lukacs's 1981 demonstration of zone electrophoresis in open fused-silica capillaries showed that the high field strengths possible in narrow capillaries gave exceptionally efficient separations, launching modern capillary electrophoresis and its central role in automated DNA sequencing.

Key figures

• James W. Jorgenson
• Krynn D. Lukacs
• Arne Tiselius

Seminal works

• jorgenson1981
• skoog2017

Frequently asked questions

How does capillary electrophoresis differ from chromatography?

Chromatography separates by differential partitioning between two phases, whereas capillary electrophoresis separates charged species by their migration in an electric field, so it depends on charge-to-size ratio rather than chemical affinity for a stationary phase.

What is electroosmotic flow?

It is the bulk movement of buffer through the capillary caused by the applied field acting on ions near the charged capillary wall; it carries even neutral and oppositely charged species toward the detector and largely sets the overall migration direction.