Classification from the chromatographic principle, ion chromatography is a kind of liquid chromatography, but due to some differences in structure and analysis objects between them, it is generally regarded as an independent chromatographic category. The difference between them is mainly seen from two aspects, that is, the structure of the instrument and the scope of application.
1) In terms of instrument structure, both IC and LC have solvent delivery systems, sample injection systems, detection systems, and signal recording and processing systems. However, due to the different mobile phases , the detection methods and signals are different. The processing requirements are different, and there are some differences in each component.
A. Ion chromatography generally uses an aqueous solution of acid, base and salt as the mobile phase, so usually non-metallic materials are used as the material of the entire system, and Peek plastic is generally used as the pump body, flow path and valve body and other parts that require high pressure resistance. The polytetrafluoroethylene material is used as a detector, an external pipeline, etc., and the system is required to be resistant to acid and base.However, liquid chromatography generally uses organic solvents as eluents, so most of them still use metal pumps, which can withstand any type of organic solvents, but acid or base solvents are prone to corrosion when used.
With the wide application in the biological field, metals have a certain adsorption effect on some biologically active compounds, and some liquid chromatography in biological applications also widely uses Peek materials as the pump body, flow path and valve, so that the they have a certain versatility.
B. At present, the suppressed type ion chromatography is widely used ,which has a suppressor , while ordinary liquid chromatography does not have a similar device.
C. Another difference between them is the detector. In general, liquid chromatography uses a UV-visible photometric detector; while ion chromatography is more common with a conductivity detector.
2) Another difference between them lies in the analysis object. Generally, when liquid chromatography is used, the measured object is required to have a certain photometric absorption, so it can generally be used for the analysis of organic compounds.Ion chromatography mainly uses the characteristics of ionization of ions in aqueous solution to generate conductivity, so it is mainly used for the analysis of inorganic ions.
D.Column Differences. Due to the relationship of the eluent, ion chromatography columns are generally polymer columns, mainly styrene and divinylbenzene columns, with a higher column efficiency of about 30,000, while conventional liquid chromatography columns are more commonly used silica gel The matrix column is mainly reversed-phase, and the column efficiency is generally above 60,000.
E .gas path
Due to the different designs of different manufacturers, some instruments rely on pneumatics, and are stabilized by gas protection eluent (NaOH system), and the gas consumption is not large; while in liquid chromatography, only ELSD and MS detectors use gas sources. And it uses a lot of gas.
F mobile phase (eluent)
Ion chromatography generally uses a strong acid and strong base water system, the pH can be 0-14, and some reversed-phase organic solvents are added, and some inorganic salts are also used. The liquid chromatography is mostly organic phase, the pH is mostly between 2-8.5, there are many kinds of organic reagents, and the use of mobile phase additives is more flexible.