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What is the principle of ion chromatography?

Time:2018/09/20   Pageviews:0    Share:
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Ion Chromatography is a type of high performance liquid chromatography (HPLC) that is a liquid chromatography method for the analysis of anions and cations.

The basic principle of ion chromatography

The separation mechanism of ion chromatography is mainly ion exchange. There are three separation methods, which are high performance ion exchange chromatography (HPIC), ion exclusion chromatography (HPIEC) and ion pair chromatography (MPIC). The resin skeleton used for the column packing of the three separation methods is basically a copolymer of styrene-divinylbenzene, but the ion exchange functional groups and capacities of the resins are different. HPIC uses low-capacity ion exchange resins, HPIEC uses high-capacity resins, and MPIC uses porous resins that do not contain ion exchange groups. The three separation methods are each based on different separation mechanisms. The separation mechanism of HPIC is mainly ion exchange, HPIEC is ion exclusion, and MPIC is mainly based on adsorption and ion pair formation.

1. High-efficiency ion exchange chromatography autosampler vials

Using the principle of ion exchange, ion exchange resin with low exchange capacity is used to separate ions, which is the most widely used in ion chromatography. The main filler type is organic ion exchange resin, and the styrene divinylbenzene copolymer is used as the skeleton in benzene. Introducing a sulfonic acid group on the ring to form a strong acid type cation exchange resin, and introducing a tertiary amine group into a quaternary amine type strong basic anion exchange resin having a macroporous or thin shell type or a porous surface layer type physical structure, so that In order to quickly achieve exchange balance, the ion exchange resin can be used in any pH range. It is easy to regenerate and has a long service life. The disadvantages are poor mechanical strength, easy swelling and contamination by organic substances. The silicon-bonded ion exchanger uses silica gel as a carrier to react an organosilane having an ion exchange group with a silanol group on the surface to form a chemically bonded ion exchanger, which is characterized by high column efficiency, fast exchange balance, and mechanical strength. High, the disadvantage is that it is not resistant to acid and alkali, and should only be used within the pH28 range. Ion exchange chromatography is the most commonly used ion chromatography.
2. Ion exclusion chromatography

It is mainly based on the Donnon membrane repulsion effect, the ionization component is not retained by rejection, and the weak acid has a certain retention principle. The ion exclusion chromatography is mainly used to separate organic acids and inorganic oxyacids such as borate carbonate and sulfuric acid. Root organic acid, etc. It mainly uses a high exchange capacity sulfonated H-type cation exchange resin as a filler with dilute hydrochloric acid as the eluent.

3. Ion pair chromatography

The stationary phase of ion-pair chromatography is a hydrophobic neutral filler. It can be used as styrene divinylbenzene resin or octadecyl silica gel (ODS). It can also be used as C8 silica gel or CN. The mobile phase of the stationary phase consists of so-called counter ion reagents and The composition of an aqueous solution of an appropriate amount of organic solvent means that the charge is opposite to the ion to be detected and can form a hydrophobic ion with it, and the surfactant ion for the compound is an alkylamine such as an ion for anion separation. The counter ion used for cation separation is an alkyl sulfonic acid, such as sodium hexane sulfonate, sodium heptane sulfonate, etc., which is hydrophilic to the non-polar terminal lipophilic polar end of the ion, and the longer the CH2 bond, the ion pair The stronger the retention of the compound in the stationary phase, the more the organic solvent is added to the polar mobile phase to accelerate the leaching rate. This method is mainly used for the separation of hydrophobic anions and metal complexes, and the separation mechanism is Three different hypotheses, reversed ion pairs, distribute ion exchange and ionic interactions.

Ion chromatography system

The IC system is constructed in the same way as HPLC vials. The instrument consists of a mobile phase transfer section, a separation column, a detector, and a data processing unit. It is usually equipped with an MSM or similar suppressor when it is necessary to suppress the background conductance. The main difference is that the mobile phase of the IC requires acid and alkali corrosion resistance and a system that does not swell in water-miscible organic solvents such as acetonitrile, methanol and acetone. Therefore, all pipes, valves, pumps, columns and joints through which the mobile phase passes should not be made of stainless steel, but a plastic IC system of PEEK material resistant to acid and alkali corrosion. The most important component of ion chromatography is the separation column. The column material should be inert and generally used at room temperature. The successful development of high-efficiency columns and special performance separation columns is the key to the rapid development of ion chromatography.

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