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Capillary Electrophoresis Principles
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Capillary Electrophoresis Principles
Capillary Electrophoresis Principles
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Question
What is the fundamental principle behind capillary electrophoresis (CE)?
Answer
Capillary electrophoresis separates charged analytes based on differences in their migration properties inside a capillary under an applied electric field.
Question
Who were two key scientists associated with the development and improvement of electrophoresis?
Answer
Arne Tiselius developed electrophoresis for serum protein study in the 1930s, and James W. Jorgenson introduced fused silica capillaries in the 1980s, significantly improving the technique.
Question
What material are capillaries typically made of in CE, and what are typical dimensions?
Answer
CE uses fused silica (SiO2) capillaries with lengths up to 100 cm, inner diameters between 25 and 150 µm, and an external diameter of about 350–375 µm, often coated with polyimide for mechanical strength.
Question
What major forces control the behavior of analytes inside a capillary during CE?
Answer
Electrophoresis (migration of ions under an electric field) and electroosmosis (bulk movement of liquid) are the two main phenomena controlling analyte behavior.
Question
Define electrophoresis in the context of capillary electrophoresis.
Answer
Electrophoresis is the movement of charged ions in solution under the influence of an electric field, where cations move toward the cathode and anions toward the anode.
Question
What is electrophoretic mobility (µ_ep) and how does it relate to ion migration speed in CE?
Answer
Electrophoretic mobility is the proportionality constant relating an ion's speed to the strength of the electric field; it depends directly on ion charge and inversely on friction (size and viscosity).
Question
Write the equation expressing migration velocity (ν) of an ion in CE and define each term.
Answer
ν = µ_ep * E = (µ_ep * V) / L_T - ν = migration velocity (m/s) - µ_ep = electrophoretic mobility (m²/V·s) - E = electric field strength (V/m) - V = applied voltage (V) - L_T = total capillary length (m)
Question
How does ion size affect electrophoretic mobility and migration velocity?
Answer
Larger ionic radius increases friction, which lowers electrophoretic mobility, thus reducing migration velocity in the electric field.
Question
Explain the friction coefficient (f) in the context of ion mobility, and how is it calculated?
Answer
The friction coefficient describes resistance to ion movement, calculated as f = 6πηr, where η is viscosity of the medium and r is ion radius.
Question
Why are fused silica capillaries coated with polyimide in CE instrumentation?
Answer
Polyimide coating provides mechanical robustness to the delicate fused silica capillaries, preventing breakage during handling and use.