Abstract: The separation mechanism of ion chromatography includes three separation methods: high performance ion exchange chromatography (HPIC), ion exclusion chromatography (HPIEC) and ion pair chromatography (MPIC). The main one is ion exchange. The resin skeletons of the column packings used in the three separation methods are basically styrene-divinylbenzene copolymers. The ion exchange functional groups and capacities of the resins are different.
Low capacity ion exchange resins are used for HPIC, high capacity resins are used for HPIEC, and porous resins without ion exchange groups are used for MPIC. The three separation methods are based on different separation mechanisms. The separation mechanism of HPIC is mainly ion exchange, HPIEC is mainly ion exclusion, and MPIC is mainly based on adsorption and ion pair formation.
1. High-efficiency ion exchange chromatography
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, with styrene divinylbenzene copolymer as the skeleton, in benzene Introduce sulfonic acid groups on the ring to form strong acid type cation exchange resin, and introduce tertiary amine group to form quaternary amine strong basic anion exchange resin. This exchange resin has a large pore or thin shell type or porous surface layer type physical structure, In order to reach the exchange equilibrium quickly, 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 organic contamination.
Silicon-bonded ion exchangers use silica gel as a carrier to react organosilanes with ion-exchange groups with silanol groups on the surface of the substrate to form chemically-bonded ion exchangers, which are characterized by high column efficiency, fast exchange balance, and mechanical strength High, the disadvantage is that it is not resistant to acids and alkalis, and should only be used in the pH range of 28.
Ion exchange chromatography is the most commonly used ion chromatography.
2. Ion exclusion chromatography
It is mainly based on the Donnon membrane repulsion effect. Ionized components are not retained by repulsion, while weak acids have a certain retention principle. Ion repulsion chromatography is mainly used to separate organic acids and inorganic oxo acid radicals, such as borate carbonate and sulfuric acid. Root organic acids, etc. It mainly uses sulfonated H-type cation exchange resin with high exchange capacity as filler and dilute hydrochloric acid as eluent.
3. Ion pair chromatography
The stationary phase of ion pair chromatography is a hydrophobic neutral filler, which can be styrene divinylbenzene resin or octadecyl silica gel (ODS), and also C8 silica gel or CN. The stationary phase mobile phase consists of a so-called counter ion reagent and An aqueous solution of an appropriate amount of organic solvent. The counter ion means that its charge is opposite to the ion to be measured and can generate hydrophobic ions with it. For the surfactant ion of the compound, the counter ion used for anion separation is alkylamines such as hydrogen. Tetrabutylammonium oxide hexadecyltrimethane hydroxide, etc., the counter ion used for cation separation is alkyl sulfonic acids, such as sodium hexanesulfonate, sodium heptane sulfonate, etc. The polar end of the lipid is hydrophilic. The longer the CH2 bond, the stronger the ion retention of the compound in the stationary phase. In the polar mobile phase, some organic solvents are often added to speed up the elution rate. This method is mainly used for hydrophobicity. There are three different hypotheses for the separation mechanism of anions and metal complexes. The reversed ion pair distribution ion exchange and ion interaction.
Causes and solutions of common problems of ion chromatography
Problem cause solution
Sudden drop in pressure with air bubbles or open degassing device
Leakage inspection pipeline in the system
The pump head needs maintenance and inspection to clean the pump head, valve and sealing ring
The pressure rises suddenly. The eluent has small solid particles; it may be that the quality of the high-purity water is poor or the contamination of the filter starts from the detector end of the flow path.
The British blue filter is blocked at 6.2821.120 Replace the filter element 6.2821.130
MSM chemical suppressor (hereinafter referred to as MSM)-plugging MSM regeneration treatment (regeneration liquid: 1mol / LH2SO4 0.1mol / L oxalic acid and 5% acetone)
Is the conductivity detector clogged? Cut the outlet PEEK tube a few millimeters
Flush the detector in the direction opposite to the normal flow direction
Guard column-plug replacement guard column
Separation column-plugged? Regeneration treatment separation column
Six-way valve-clogged six-way valve to clean the inside of the six-way valve
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