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Capillary Electrophoresis Introduction

Capillary electrophoresis is a technique used to separate ions on basis of their electrophoretic mobility. It is an analytical technique which is used by applying voltage.

In this technique, the charge of the molecule is crucial as the electrophoretic mobility depends on it. The radius of the atom and viscosity also plays a vital part. The ability to provide quick result make capillary electrophoresis used predominately.

What is Capillary Electrophoresis?

The capillary electrophoresis technique is classified in the group of separation techniques mainly used to separate and analyze ions (or the given sample) based on their relevant mobilities under the influence of applied voltage.

The mobility of every ion is different from others based on its specific viscosity, molecular charge, and atomic radius. Therefore, whenever we apply a specific electric voltage over the given sample of ions, they move uniquely and get identified.

The entire procedure of CE is performed in a small glass tube - the capillary tube that contains a special electrolyte solution filled in it. After filling the matrix of capillaries with electrolytes, the sample is introduced into the same capillary tube. In the end, both the ends of the U-shaped capillary are dipped into buffers.

As soon as an electric voltage is applied, the ions present in the molecules begin to move towards opposite charges in this electric chemical reaction. In the end, we get the result, consisting of quantitative and qualitative data of ions. The results are measured using the detector.

The capillary tube used during CE is usually silica - either coated or uncoated. Similarly, the detector used in this procedure is a UV absorption detector. Based on the capillary electrophoresis instrument and procedure used during this electrophoresis separation technique, there are two types of capillary electrophoresis techniques called capillary gel electrophoresis and capillary zone electrophoresis.

What is Capillary Gel Electrophoresis?

Capillary gel electrophoresis, as stated before, is a separation technique based on the capillary electrophoresis principle. However, in this technique, we separate the charged molecules using the capillaries wherein a porous gel fluid is filled previously.

Which type of fluid should be filled in the matrix of capillaries depends upon your separation needs. Mainly, there are two types of gels used; chemical gels (permanent ones) and physical gels (reversible ones).

If you notice more attentively then you'll see that the capillary electrophoresis DNA is nothing but an upgrade of slab gel electrophoresis which is modified slightly by mixing it with the basic CE technique.

The capillary gel electrophoresis technique is mainly used to analyze and separate large or macro bio-molecules like DNA, protein, and RNA. The entire procedure of capillary gel electrophoresis consists of four major steps

  1. The starting and ending vessels and both the adjoined capillary tubes are filled with a special electrolyte aqueous solution.
  2. The sample, consisting of molecules to be separated, is poured into the capillaries.
  3. A specific electric voltage is applied and the ions start to migrate towards their corresponding electrodes; opposite charges.
  4. The separated molecules are quantified using the principles of spectrometry, absorbance, and fluorescence.

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The basic difference between CGE and CE is that the CGE is performed in the horizontal or vertical plane, filled with a porous polymer gel. On the other hand, the capillary electrophoresis is performed in a standard capillary tube, filled with a gel or a liquid polymer.

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What is the Principle of Capillary Zone Electrophoresis?

This separation technique is also used to analyze and separate peptides, proteins, nucleic acids and other macromolecules. However, the thing which makes it different from CGE is that it is used for the detection of inorganic compounds - separating a sample consisting of inorganic anions and cations.

All these ionic separations are done in CZE due to two basic phenomena; electroosmotic mobility and electrophoretic mobility. The electroosmotic mobility results from the usual or general flow of water (solvent) towards the cathode.

On the other hand, the electrophoretic flow results from the movement of differently charged species under the electric field. Anions move towards the anode (the positive end) of the capillary whereas the cations move towards the cathode (the negative end) of the capillary.

Where the charged species will move depends upon the mass and type of charges. The neutral substances, present in the sample, do not react to the applied electric voltage.

Related: Also read about the sodium and chlorine reaction to balance the chemical equation.

What is Capillary Electrophoresis Used For?

This technique is widely being used in the fields of nano and microfluidics where it is used to separate and detect various ionic species from one another, quickly and with utmost precision. Similarly, the CE technique is also quite helpful to identify a wide range of organic compounds and biological molecules including nucleic acid and proteins by using capillary electrophoresis instrument. Other applications of CE in daily life are as follows

  • The technique of CE is a highly popular alternative to the LC separation method in the pharmaceutical industry as it is more cost-effective and time-efficient.
  • CE is used widely in clinical sciences and diagnostic analysis.
  • The technique of CE is also very helpful in forensic testing, like capillary electrophoresis DNA, CE genetic testing and blood sample evaluation etc.

The main reason why this technique is replacing the other separation methods so rapidly is because it requires a very little sample, is automated, easy to perform, cost-effective, and can be used with equal excellence to separate both charged and uncharged species. There are also other techniques of seperation are available like techniques of spectrophotometry as well as NMR spectroscopy which you can read on this site.

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