What Are Capillaries?

A tube with a very small inner diameter is called a "capillary tube". Usually refers to a thin tube with an inner diameter equal to or less than 1 millimeter. Because the diameter of the tube is as thin as a hair, it is called a capillary. Currently used in medicine, building materials.

Definition: When an object containing a fine gap comes in contact with the liquid, the liquid rises or infiltrates along the gap under the condition of infiltration, and the liquid descends along the gap without infiltration. In the case of infiltration, the finer the gap, the higher the liquid rises. It means that the liquid on the inside of the thin tube is overcome by the difference in cohesion and adhesion.

Capillary electrophoresis (CE), also known as high performance capillary electrophoresis (HPCE), is a new type of liquid phase separation technology that uses a capillary as a separation channel and a high-voltage DC electric field as a driving force. Capillary electrophoresis actually includes electrophoresis, chromatography, and crossovers. It enables analytical chemistry to move from microliters to nanoliters, and enables single-cell analysis and even single-molecule analysis. The separation and analysis of biological macromolecules, such as proteins, which have long plagued us, have also brought about new opportunities.

Capillary electrophoresis usually uses a flexible (polyimide) coated fused silica tube with an inner diameter of 25-100 m. The standard capillary has an outer diameter of 375 m, and some tubes have an outer diameter of 160 m. The characteristics of the capillary are: small volume (the volume of a 100 cm × 75 m tube is only 4.4 L); the side / cross-sectional area ratio is large, so it dissipates heat quickly, and can withstand high electric fields (100-1000 V / cm); Solutions, gels, etc. are the supporting medium; in the solution medium, an electroosmotic flow with a planar shape can be generated.

Therefore, capillary electrophoresis can have the following advantages:

(1) The number of high-efficiency trays is between 105-106 plates / m. When using CGE, the number of trays can reach 107 plates / m or more;

(2) The separation is usually completed within ten minutes quickly;

(3) The sample volume required for micro-injection is nL;

(4) Multi-mode can choose different separation modes according to needs and requires only one instrument;

(5) The economic experiment consumes only a few milliliters of buffer solution, and the maintenance cost is very low;

(6) Automatic CE is the current separation method with a high degree of automation.

The disadvantages of capillary electrophoresis are:

(1) The preparation capacity is poor due to the small amount of injection;

(2) Due to the small diameter of the capillary, the optical path is too short. When using some detection methods (such as ultraviolet absorption spectroscopy), the sensitivity is low;

(3) Electroosmosis will change due to sample composition, which will affect separation reproducibility. ^[3]