Since the birth of Ion Chromatography in 1975 more than 40-year rapid development, ion chromatography has gradually become a common method for the analysis of ionic substances, organic acids, and sugars by virtue of its unique advantages. With the increasing attention to the environment and the continuous improvement of ion chromatography-related technologies, the future application prospects of ion chromatography in the environment, food, pharmaceuticals, biomedicine, and other fields can be expected.
Principles of ion chromatography
The well-known chromatographic technique utilizes the difference in physical and chemical properties of the mixture to be separated so that the components are distributed in the stationary phase and the mobile phase to varying degrees. Due to the components advance with the mobile phase at different speeds, the components can be effectively separated. As a special high-performance liquid chromatography, ion chromatography is also based on physical separation methods.
Ion chromatography has three types: ion exchange chromatography, ion exclusion chromatography, and ion pair chromatography. The most widely used is ion-exchange chromatography (high-efficiency ion-exchange chromatography).
The main packing type of ion-exchange chromatography column is organic ion exchange resin. The filler takes the cross-linked copolymer of styrene and divinylbenzene as the skeleton and introduces sulfonic acid groups on the benzene ring to form a strong acid cation exchange resin. Or introduce tertiary amine groups to form a quaternary amine type strongly basic anion exchange resin. This exchange resin has a physical structure of large pores, thin shell type, or porous surface layer type in order to quickly reach the exchange balance. The advantages of ion exchange resins are that they are acid-base, can be used in any pH range, are easy to regenerate, and have a long service life. The disadvantages are poor mechanical strength, soluble, and are contamination by organic matter.
Ion chromatography with ion exchange resin as the stationary phase usually uses acidic or alkaline aqueous solution as the mobile phase, and finally realizes separation according to the difference in ion exchange capacity of different ions to be measured and the stationary phase. The affinity between each component to be tested and the ion exchanger is related to the ion radius, charge, and ion existence form. The greater the affinity, the longer the retention time of the analyte in the stationary phase.
With the continuous advancement of technology, insoluble and non-ionizable substances can also be transformed into detectable forms through pretreatment.
Advantages of ion chromatography
1.Simultaneous analysis of multiple ions
Ion chromatography can measure a certain ion individually, and the analysis method is simple and quick. In addition, ion chromatography can one injection and can analyze multiple ions without separate operations. At present, some ion chromatographic column technology has achieved one injection, and it can analyze more than 30 kinds of ions at the same time, and all the information of anions, cations, and sample composition can be obtained in a short time.
2.Good data reproducibility
This is a characteristic of automated analytical instruments. Traditional methods such as titration methods, depending on the level and ability of the operator, obtain different results. The current instrument has a higher degree of automation. Only needs to inject the sample into the equipment, the process of separation, detection, and reporting can complete automatically, and different operators will not affect the results.
3.Fast and convenient
Ion chromatographic analysis of conventional 7 kinds of standard anions (nitrite, nitrate, sulfate, phosphate, fluoride ion, chloride ion, and bromide ion) and 6 kinds of cations, lithium ion, sodium ion, ammonium ion, potassium ion The separation of magnesium ions and calcium ions can be completed within half an hour. If you use a high-efficiency fast chromatographic column, the speed is faster and can be completed within 10 minutes, which will greatly shorten the manual operation time.
4.Separate ions of different shapes and valences
This is the outstanding advantage of ion chromatography, which can separate ions of different shapes and valences. Such as the separation of nitrite and nitrate, the traditional spectrophotometric method. Since the absorbance values of nitrite and nitrate are very close, they cannot be separated well. However, nitrite and nitrate can be separated better by ion chromatography.
The sensitivity of ion chromatography is high, and the analysis concentration range is usually low μg/L～mg/L, and generally can reach the level of μg/L. If the injection volume is increased, a small aperture column or online concentration method can be used to improve the sensitivity. The detection limit is even lower, even reaching ng/L.
1.Environmental protection industry
In the environmental protection industry, ion chromatography is widely used in water quality analysis, air pollution analysis, soil and biological pollution, and fossil dye analysis. Various inorganic anions, cations, and organic acids in various water quality standards can be determined by ion chromatography. Such as potassium ions, sodium ions, lithium ions, calcium ions, etc. in water quality analysis.
Ion chromatography is widely used in food testing. Such as the detection of nitrate and nitrite. Nitrate and nitrite are used as food additives, so it is necessary to detect their residual amount in food. For the determination of nitrate, cadmium column reduction and spectroscopic breadth analysis is widely used in the world to determine nitrate. The operation is often cumbersome, time-consuming, and labor-intensive. If ion chromatography is used, the detection speed and sensitivity can be improved, and sample pretreatment procedures can be simplified.
In addition to the above fields, the analysis of pesticides, fertilizers, and soil in agriculture. The analysis of blood, urine, human trace elements in biomedicine. Analysis of metallic materials and semiconductor materials in materials. The composition analysis of cosmetics, detergents, and detergents in daily chemicals. The use of ion chromatography analysis is highly efficient and accurate.