Capillary electrophoresis (CE, or, originally, high performance capillary electrophoresis) is a relatively new technique which relies on a separation and subsequent quantification of the components of the complex mixtures. The separation is based on the differential migration of the components inside the quartz capillary under the influence of the applied electric field. Lumex has designed and put on the market Capel CE series of instruments which feature all advantages typical for capillary electrophoresis:
- Since migration of the analytes occurs due to electrically-driven forces, no high pressure precision pumps are needed
- Very low reagents and samples consumption
- Very low analysis cost
- Very fast analysis time
- The absence of any solid material in the capillary excludes the problems of its aging, chemical or physical destruction or unspecific binding with sample constituents
- Separation efficiency can be extremely high, up to 1.000.000 theoretical plates
Scope of application: Since CE ensures very high separation efficiency, it can be used for the separation of numerous compounds with very similar structure. It is widely used in pharmacology and pharmacokinetics for the analysis of drugs (including drugs of abuse) in raw materials and in biological fluids, in environmental studies for the analysis of pollutants, inorganic cations and anions, in chemical and food industry for technological and quality control and in various fields of scientific research (analysis of proteins, peptides, oligonucleotides, viruses, etc.).
Usually, the capillary is filled with an appropriate buffer. The sample solution is injected from the inlet end of the capillary, electric field is applied to the capillary ends and the components migrate to the detector point with different velocities due to the differences in their electrophoretic properties. Consequently, they reach detector at different times. Results are present as a sequence of peaks, where each peak represents ideally one component. Peak area or peak height indicates the initial concentration of the component in the mixture.
The main parameter, which provides electrophoretic differentiation of the components in CE, is their charge-to-mass (e/m) ratio. Since this ratio is highly characteristic, CE separation shows a very high resolution and is suitable for the analysis of almost all classes of compounds. The presence of ionisable groups (- Si - OH) on the inner surface of the quartz capillary gives rise to a phenomenon called electroosmotic flow, which is just a bulk flow of the whole liquid inside the capillary, occurring upon applying the voltage. Electroosmotic flow enables simultaneous determination of positive and negative charged compounds in one run. Even neutral compounds can be analysed in one run together with charged species provided a surfactant (e.g. sodium dodecyl sulphate) is added to the buffer to form a micellar phase. This mode of CE, called micellar electrokinetic chromatography is a very successful combination of electrophoretic and chromatographic methods in which separation of compounds is based on the differences in their charge-to-mass ratio and hydrophobic/hydrophilic properties. Several other modes of CE can be realised on Capel instruments regarding the nature of separated solutes and general goals of the analysis. They are e.g. capillary gel electrophoresis, capillary isoelectric focusing and capillary electrochromatography.
In the most of cases UV lamp is used as a source of the light at the detector point. Monochromator, placed on the most upgraded Capel-105M CE system, gives the highest flexibility to the user enabling selection of the most appropriate wavelength for the detection and spectral scanning of the separated compounds. Compounds which do not absorb light in the UV range (e.g. inorganic ions), can be analysed in the indirect mode with a certain UV - absorbing additive in the buffer.
