Chemistry 311: Basic CE and IMD

Capillary Electrophoresis: This is a type of separation based on migration of ions under the influence of an electric field (Electrophoresis) in a small inner diameter capillary tube.

Chemistry 311: Basic CE and IMD

Resolution: Capillary Electrophoresis (CE) provides unparalleled resolution due to the elimination of key terms from the van Deemter equation. This resolution is an order of magnitude better than traditional chromatography, 50,000 to 500,000 theoretical plates are routinely obtained. In CE broadening results primarily from diffusion based mechanisms, thus, longer columns do not improve resolution.

N = µeV

2D

Chemistry 311: Basic CE and IMD

Electroosmotic Flow (EOF): Describes the movement of a liquid in contact with a solid surface under the influence of a tangential electric field.

Electroosmotic velocity, ueo ueo = µeo E Where: E = applied potential

µeo = Electroosmotic mobility m2/(Vs) Electrophoretic velocity, uep uep = µep E = (q/f) E Where: E = applied potential: µep = Electrophoretic mobility

q = charge on the ion: f = friction coefficient, spherical (f= 6πηr) η= fluid viscosity: r = ion radius

Chemistry 311: Basic CE and IMD

Apparent Mobility, µapp: The observed mobility of an ion is a function of the Electroosmotic mobility of the solution ion as well as the Electrophoretic mobility of the individual ion. Apparent Mobility µapp = µep + µeo ∴ for an analyte cation moving in the same direction as the EOF, µep and µeo have the same sign, so µapp > µep. For anions, µep would have an opposite sign and anions would only reach the detector if µeo > µep (usually requires high pH)

Chemistry 311: Basic CE and IMD

Resolution and Resistive Heating: Theoretically, since only time dependant diffusion leads to peak broadening and rate of analyte transport through the capillary is directly related to the magnitude of the applied field; then it would appear that increasing the applied voltage and shortening the capillary would continuously increase resolution. Joule heating: The voltage applied to a capillary causes a flow of current which in turn generates a quantity of heat based on the current and the resistance to flow; heat = RI2 ; This effectively limits the Voltage (V=RI) Capillaries have a much larger surface area and thus can disperse heat better

than electrophoresis slabs, thus part of the reason that higher voltages and thus,

higher resolution can be obtained. Another practical effect is that the inner

channel of the capillary tube is slightly warmer than the outer layer (0.02 – 0.3 K).

This tends to disturb the “flat” flow profile of EOF and thus adds to broadening.

this also favors the use of small capillaries (< 50 µm).

Chemistry 311: Basic CE and IMD

Instrumentation:

Chemistry 311: Basic CE and IMD

Sample Injection:

Chemistry 311: Basic CE and IMD

Separations in CE: The main separation mechanism is based on mobility differences of the analytes in an electric field; these differences are dependent on the size and charge-to-mass ratio of the analyte ion. Analyte ions are separated into distinct zones when the mobility of one analyte differs sufficiently from the mobility of the next. Capillary zone electrophoresis (CZE) uses this as the primary separation mode. (MECC), , , and Chiral CE. In Micellar electrokinetic capillary chromatography (MECC) the separation is similar to CZE, but an additional mechanism is in effect that is based on differences in the partition coefficients of the solutes between the buffer and micelles present in the buffer. In Capillary gel electrophoresis (CGE) an additional mechanism is based on solute size, as the capillary is filled with a gel or a polymer network that inhibits the passage of larger molecules. In Chiral CE an additional separation mechanism is based on chiralselectivity In capillary electrochromatography (CEC) the capillary is packed with a stationary phase that can retain solutes on basis of the same distribution equilibria found in chromatography

Chemistry 311: Basic CE and IMD

Chemistry 311: Basic CE and IMD

Chemistry 311: Basic CE and IMD

Chemistry 311: Basic CE and IMD

Chemistry 311: Basic CE and IMD

Chemistry 311: Basic CE and IMD

Detectors for Capillary Electrophoresis:

Chemistry 311: Basic CE and IMD

Indirect Detection:

Chemistry 311: Basic CE and IMD

CE/MS:

Chemistry 311: Basic CE and IMD

Chemistry 311: Basic CE and IMD