Content1. What is capillary electrophoresis instrument?
1.1 Working principle of capillary electrophoresis instrument
1.2 History of capillary electrophoresis instrument
1.3 Basic construction of capillary electrophoresis instrument
1.4 Working process of capillary electrophoresis instrument
1.5 Feature of capillary electrophoresis instrument2. Application of capillary electrophoresis instrument
3. Use of capillary electrophoresis instrument
4. How to buy capillary electrophoresis instrument?
What is capillary electrophoresis instrument?
Capillary electrophoresis instrument is a laboratory instrument that separates components by using a flexible quartz capillary as the separation channel and a high voltage DC electric field as the driving force and then separates the components according to the differences in the flow rate (migration rate per unit electric field strength) and distribution behavior of each component in the sample.
Working principle of capillary electrophoresis instrument
When the electrolyte is loaded and run in a capillary electrophoresis column, electroosmotic flow is generated due to the presence of silicone hydroxyl groups in the wall of the tube, and the solution inside the entire capillary column moves in a directional manner driven by the electroosmotic flow. The separation principle is based on the difference in ion migration velocity under the action of the electric field, which is the main difference from the general chromatographic technique, rather than on the partition coefficient of the components in the mobile and stationary phases.
History of capillary electrophoresis instrument
|1967||First to perform zonal electrophoresis of free solutions in 3mm diameter capillaries.
|1974||Separation by electrophoresis in 200~500μm inner diameter capillaries.
|1981||Electrophoresis was achieved by using a 75μm inner diameter glass capillary column with a voltage of 30kV.
|1984||Introduced micellar capillary electrokinetic chromatography.
|1987||Realized capillary isoelectric focusing and capillary gel electrophoresis.
|1988||Introduced CE as the first micro-liquid extraction, and introduced laser into CE detector, which greatly improved the detection sensitivity.
Basic construction of capillary electrophoresis instrument
The main components of the capillary electrophoresis instrument are DC high voltage power supply, capillary tube, electrode, and electrode bath, rinse feed system, detection system, and data processing system. The same buffer as inside the capillary tube is packed in two buffer bottles. The two ends of the capillary tube are placed in the two buffer bottles, and platinum electrodes are inserted in each of the two buffer bottles. During the experiment, the electrolyte solution in the two buffer bottles should be kept at the same liquid level and the ends of the capillary tubes should be inserted at the same depth below the liquid level because the siphoning effect caused by the pressure difference between the ends of the capillary tubes results in the flow of the solution, which affects the analysis results.
A. Capillary column
The equipped capillary column is usually of round tube type, which should be chemically and electrically inert, light-transmissive, flexible, and easy to bend. The inner diameter of the capillary column should be less than 140 microns, which makes it have better heat dissipation. Currently, capillary columns with an inner diameter between 25 and 75 microns are the most commonly equipped.
Material of capillary column
Quartz is the most common material used to make capillary columns. The basic component of quartz is silicon dioxide, which is divided into natural quartz and artificial quartz.
Of all materials, glass has the strongest electro-permeability. However, glass material contains impurities.
Polytetrafluoroethylene has properties such as UV permeability and weak electro-osmosis. The disadvantages of using PTFE are that the tubes do not have a uniform inner diameter, adsorption to the sample, poor heat transfer, etc.
The detectors are usually UV or laser-induced fluorescence detectors.
C. High voltage power supply
Equipped with 0-30 kV, 200-300 mA high voltage power supply.
D. Sampling technology
a. Motorized injection, also known as electromigration injection.
b. Pneumatic injection, also known as differential pressure injection, refers to the siphoning action by pressurizing the inlet side and depressurizing the outlet side.
E. CE buffering system
|CE buffering system||Range
|Sodium phosphate system||Wide buffer range
|Sodium borate system||High pH range
|Tris-HCI system||Low pH range
|Acetic acid-ammonium acetate system||CE/MS common systems
Working process of capillary electrophoresis instrument
a. Filled the buffer into the capillary column.
b. Injecting end is replaced with cuvette injection.
c. Switch back to buffer pool.
d. High voltage applied.
e. Separation of components due to flow and distribution differences.
f. UV or laser-induced fluorescence detector.
g. Data recording and processing system.
Application of capillary electrophoresis instrument
Capillary electrophoresis system
A. Medical and clinical testing
Applications of capillary electrophoresis
in medical and clinical testing include pathological testing of patients, disease diagnosis, analysis of disease mechanisms, and analysis of metabolites in vivo. The objects of analysis are drugs, disease-related markers, ions in body fluids or tissues, etc.
B. Drugs and natural products
CE analysis and detection of drugs or natural products mainly include synthetic drugs, protein drugs, and active ingredients of plants.
C. Food and agricultural products
Due to the increasing attention to food safety issues, the number of CE methods used for food safety and agricultural product testing has increased year by year. Food safety testing mainly includes the detection of food additives, certain components, or harmful ingredients in food. Agricultural product testing includes pesticide residues and active ingredient testing of agricultural products.
CE has the advantage of detecting biological macromolecules such as proteins, nucleic acids, and sugars. It is also widely used for the detection of biological small molecules or metabolic intermediates.
E. Chiral analysis
CE can be used for chiral splitting, such as enantiomeric separation of amino acids or small molecules, drug molecules, and comparison and evaluation of chiral splitting agents.
F. Environmental monitoring
can be used to directly sample contaminated water without pretreatment, thus rapidly detecting antibiotics, hormones, or drugs, and heavy metal ions in water.
Use of capillary electrophoresis instrument
Capillary electrophoresis machine
Capillary electrophoresis analysis requires a high level of injection technique, and the injection operation is as follows.
a. The smaller the sample inlet zone band the better. Regardless of the injection method, the depth of the capillary tube inserted into the sample solution should generally be less than 1% to 2% of the total length of the capillary tube. This minimizes the performance of the sample solution through the capillary adsorption into the capillary tube and affects the injection volume. If the solution in the sample tube is 5μL, the injection volume should be 1 to 50nL.
b. The injection time should be short. Usually, the injection time is 0.5 to 1s, at which time the amount of sample adhered to the capillary is negligible relative to the volume of inhalation. Although the injection time of capillary electrophoresis can be up to ±0.1s, some solution will inevitably adhere to the capillary when it is inserted into the sample tube, so a short injection time will affect the reproducibility of the analysis.
c. Sample pre-concentration. Constrained by the total volume in the capillary, for samples with very dilute concentration, capillary electrophoresis cannot increase the sample volume to improve detection sensitivity as HPLC can, but some measures can be taken to improve it.
a) When the conductivity of the sample buffer is significantly lower than that of the electrophoresis buffer by more than 100 times, the addition of voltage at both ends of the capillary can form a larger electric field in front of and behind the sample zone, which makes the molecules in the sample solution migrate faster. When these molecules reach the boundary of the electrophoresis buffer, the migration speed slows down because the electric field weakens, so that the sample zone becomes narrower and the concentration increases, and the purpose of concentration is achieved.
b) When the sample buffer and electrode buffer have the same conductance, and the sample concentration is dilute and not suitable for further dilution, some water can be inhaled before the sample is injected, which can also achieve the purpose of concentration.
c) No matter what kind of injection method is adopted, the above method can make the sample pile up and concentrate. However, due to the steep drop in potential in the stacking zone, it will lead to an increase in temperature in this zone.
d. The sample feeding operation should be started immediately after the capillary is inserted into the sample solution. After completion, the capillary should be quickly moved to the buffer to start electrophoresis. Otherwise, capillary action and siphoning will occur, causing errors and broadening of the spectral band.
e. The electrode should not be in contact with the capillary tube. The level of the sample reservoir and buffer reservoir should be balanced.
f. Keep the system as constant as possible. Because the temperature directly affects the viscosity and affects the constant amount of the sample feed.
g. The solvent in the sample solution must be mutually soluble with the buffer, and the ionic strength of the former should be lower than that of the latter.
h. Prevent evaporation and loss of sample solutions and buffers.
How to buy capillary electrophoresis instrument?
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