Ion Chromatography (IC) Introduction
Ion chromatography separation mechanism is mainly ion exchange, there are three kinds of separation methods, they are high-performance ion exchange chromatography (HPIC), ion exclusion chromatography (HPIEC) and ion-pair chromatography (MPIC). The resin scaffolds used for the column packing of the three separation methods are basically styrene-divinylbenzene copolymers, but the resin has different ion-exchange functional groups and capacities. HPIC uses a low-volume ion exchange resin, HPIEC uses a high-capacity resin, and MPIC uses a porous resin that does not contain ion-exchange groups. Three kinds of separation methods are based on different separation mechanisms. HPIC separation mechanism is mainly ion exchange, HPIEC is mainly ion rejection, and MPIC is mainly based on adsorption and ion pair formation.
1, high efficiency ion exchange chromatography
The principle of ion exchange, the use of low exchange capacity of ion exchange resin to separate ions, which is the most widely used in ion chromatography, the main filler type of organic ion exchange resin to styrene divinylbenzene copolymer as a skeleton, benzene The introduction of sulfonic acid groups on the ring, the formation of strong acid cation exchange resin, the introduction of tertiary amine into quaternary ammonium strong base anion exchange resin, the exchange resin has a macroporous or thin shell or porous surface layer type physical structure in order to To quickly achieve exchange equilibrium, ion exchange resin acid and alkali can be used in any pH range, easy regeneration process, long service life, the disadvantage is poor mechanical strength, easy to swell, organic contamination.
Silica-bonded ion exchangers are based on silica gel and react with organosilanes with ion exchange groups and silanol groups on the surface to form chemically bonded ion exchangers, which are characterized by high column efficiency, fast exchange equilibrium, mechanical strength High, the disadvantage is not Naisuan Jian, should only be used within the pH2-8 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 exclusion of ionizing components is not retained, and the weak acid has a certain retention principle, made of ion-exclusion chromatography is mainly used for the separation of organic acids and inorganic oxyacids such as borate carbonate and sulfuric acid Root organic acids and so on. It mainly uses high exchange capacity of sulfonated H-type cation exchange resin as a filler to dilute hydrochloric acid as eluent.
3, ion pair chromatography
The stationary phase of ion-pair chromatography is a hydrophobic, neutral filler that is available as styrene divinylbenzene resin or octadecyl silica gel (ODS), also useful as C8 silica gel or CN, and the stationary phase mobile phase consists of a mixture of so- An appropriate amount of an organic solvent in aqueous solution, the counter ion means that the charge opposite to the ion to be measured and to generate a hydrophobic ion, the surfactant ion of the compound, and the counter ion for anion separation are alkylamines such as hydrogen Tetrabutylammonium hydroxide cetyltrimethylammonium hydroxide and the like, and the counter ions used for cation separation are alkylsulfonic acids such as sodium hexanesulfonate, sodium heptane sulfonate and the like, Lipophilic end of the hydrophilic, the longer the CH2 bond ion retention of the compound in the stationary phase is stronger, in the polar mobile phase, often adding some organic solvents to speed up the rinse rate, this method is mainly used for hydrophobic Anion and metal complex separation, as the separation mechanism there are three different hypotheses, reverse ion pair distribution ion exchange and ionic interactions.
system introduction
The composition of the IC system is the same as that of HPLC. The instrument consists of a mobile phase transfer section, a separation column, a detector and data processing. The MSM or similar suppressor is usually provided when the background conductance needs to be suppressed. The main difference is that the mobile phase of the IC requires a system that is resistant to acid and alkali attacks and that does not swell in water-miscible organic solvents such as acetonitrile, methanol and acetone. Therefore, any mobile pipe through the pipeline, valves, pumps, columns and joints, etc. should not use stainless steel, but with acid corrosion PEEK material plastic IC system. The most important part of ion chromatography is the separation column. Column material should be inert, generally at room temperature. The successful development of high performance column and special performance separation column is the key to the rapid development of ion chromatography.
Detection method
Ion chromatography detector is divided into two categories, namely, electrochemical detector and optical detector. Electrochemical detectors include conductivity, DC ampere, pulsed ampere and integral ampere; and photochemical detectors include UV-vis and fluorescence.
With the widespread use of ion chromatography, the detection technique of ion chromatography has evolved from a single chemosuppressive conductivity method to a method that includes electrochemical photochemistry and is used in conjunction with many other analytical instruments. 1, inhibition of conductivity detection method; 2, direct conductivity detection method; 3, UV absorption spectrometry; 4, post-column derivatization spectrophotometry; 5, electrochemical method; 6, and elemental selective detector combination.
Application range
1, inorganic anion detection
Inorganic anions are the earliest and most mature ion chromatography detection methods. They include halogen anions such as fluorine, chlorine and bromine in aqueous samples, anions such as sulfate, thiosulfate and cyanide. They are widely used in drinking water Water quality testing, beer, beverages and other food safety, wastewater discharge compliance testing, metallurgical water samples, oil industry samples and other industrial products quality control. In particular, due to the halogen ions in the electronics industry, the residue is subject to more stringent restrictions, ion chromatography is widely used in halogen-free analysis and other important process control department.
Inorganic anion exchange columns are usually crosslinked resins with quaternary amine functional groups or other substances with similar properties. Common anion exchange columns such as Metrosep A supp 4-150, A supp 5-250 and the like. Commonly used eluent for the Na2CO3 and NaHCO3 according to a certain percentage of the dilute solution configured to change the composition and concentration of eluent ratio can control the retention time of different anions and peak order.
2, detection of inorganic cations
Inorganic cation detection and anion detection principle is similar, the difference is the use of a sulfonic acid cation exchange column, such as Metrosep C1, C2-150, etc., commonly used eluent system such as tartaric acid / Effective analysis of Li, Na, NH4 +, K, Ca, Mg ions in aqueous samples.
3, organic anion and cation analysis
With the development of ion chromatography technology, new analytical equipment and methods of separation continue to emerge, gradually developed to analyze some complex ions in biological samples, the more mature applications include:
1) Detection of biogenic amines
Metrosep C1 column; 2.5mM nitric acid / 10% acetone eluent; 3μL injection, which can effectively analyze putrescine, histamine, cadaverine and other components, has become an important detection system of criminal investigation and forensic science.
2) detection of organic acids
Metrosep Organic Acids Separation Column, MSM Suppressor; 0.5 mM H2SO4 as eluent for efficient analysis of compounds including lactic acid, formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, malic acid, citric acid And other organic acid composition, in the microbial fermentation industry, the food industry is a simple and effective method of separation.
3) Sugar analysis
Has now developed a variety of carbohydrate analysis tools, including glucose, lactose, xylose, arabinose, sucrose and other carbohydrate analysis methods. In the food industry is particularly widely used.
Analytical instruments
Physical property test
Environmental monitoring and analysis
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