The basic structure of the capillary electrophoresis system includes a feeding system, two buffer tanks, a high-voltage power supply, a detector, a control system and a data processing system.
1-Temperature control system; 2-High-voltage power supply; 3-High-voltage electrode tank; 4-Capillary tube; 5-Detector; 6-Low-voltage electrode tank; 7 -platinum wire electrode; 8-recording/data processing
Detection signal is the most prominent problem of CE system due to the limitation of capillary inner diameter. The ultraviolet-visible (UV) method is a commonly used detection method for CE, but it is limited by factors such as instrumentation and single wavelength. The most widely used is the diode array (PDA) detector. Conventional detectors are also laser photothermal (LIP) and fluorescence (FL) detectors with high sensitivity. In recent years, a variety of detectors such as laser-induced fluorescence (LIF), amperometric (EC) with good selectivity, conductivity (CD) assists with good versatility, and mass spectrometry (MS), which can obtain structural information, have also been generated in practical applications. So far, except for inductively coupled plasma (ICP) and infrared (IR) techniques, which are not coupled with CE, all other detection methods are coupled with CE and most of them have been commercialized. The use of CE should be based on the characteristics of the analyzed substances, select the appropriate separation mode and detector, in order to avoid the shortcomings of the strengths and get the best analytical results.
The main components of the capillary electrophoresis instrument and their performance requirements are as follows. (1)Capillary with flexible quartz capillary, inner diameter of 50μm and 75μm two kinds of use more (capillary electrochromatography sometimes use the inner diameter of the capillary and then larger). Fine inner diameter separation effect is good, and Joule heat is small, allowing the application of higher voltage, but if the use of on-column detection due to the shorter optical range detection limit is worse than the coarse inner diameter tube. The length of the capillary tube is called the total length, according to the requirements of the separation degree, can be selected from 20 to 100 cm in length, the length of the inlet end to the detector is called the effective length. The capillary tube is often coiled on the tube rack to control the operation at a certain temperature in order to control the Joule heat, the viscosity of the operating buffer and conductivity, the repeatability of the determination is very important.
(2) DC high-voltage power supply using 0 ~ 30kV (or similar) adjustable DC power supply, can supply about 300μA current, with a regulated voltage and regulated current two ways to choose.
(3) Electrodes and electrode tanks two electrode tanks into the operating buffer, respectively, inserted into the inlet end of the capillary and the outlet end and the platinum electrode, the platinum electrode is connected to the DC high-voltage power supply, positive and negative poles can be switched. A variety of models of instruments will be the sample bottle at the same time as the electrode tank.
(4) rinse sampling system each time before the injection of capillary tube to be rinsed with a different solution, the choice of automatic rinse sampling instrument is more convenient. Sampling methods include pressure (pressurized) injection, negative pressure (depressurized) injection, siphon injection and electric (electromigration) injection. The amount of sample is controlled by controlling the pressure or voltage and time.
(5) Detection systemUltraviolet-visible spectroscopic detection, laser-induced fluorescence detection, electrochemical detection and mass spectrometry detection can be used as detectors for capillary electrophoresis. Among them, UV-visible spectrophotometric detectors are the most widely used, including single-wavelength, programmed-wavelength and diode array detectors. The capillary near the exit end of the outer layer of polymer peeled off about 2mm section, so that the quartz tube wall is exposed, the capillary on each side of a quartz spotlight ball, so that the light source is focused on the capillary, through the capillary to reach the photocell. For the detection of solutes without light absorption (or fluorescence), indirect determination can also be used, i.e., in the operating buffer add additives with light absorption (or fluorescence), and peaks in the opposite direction appear when the solute reaches the detection window.
(6) The data processing system is basically the same as the general chromatographic data processing system.