Abstract: Analysts should have some general information about the ion to be measured. First, they should understand the molecular structure and properties of the compound to be tested and the matrix of the sample, such as inorganic or organic ions, the charge number of the ion, whether it is acid or alkali, hydrophilic or hydrophobic , Whether it is a surface-active compound, etc. The hydrophobicity and hydration energy of the ions to be tested are the main factors that determine which separation method to choose. Ions with high hydration energy and weak hydrophobicity, such as Cl- or K, are best separated with HPIC. Ions with low hydration energy and high hydrophobicity, such as perchloric acid (ClO4-) or tetrabutylammonium, are best separated by a hydrophilic ion exchange separation column or MPIC. Ions with a certain hydrophobicity and a significant hydration energy with pKa values ​​between 1 and 7, such as acetate or propionate, are best separated by HPICE. Some ions can be separated by either anion exchange or cation exchange, such as amino acids, alkaloids and transition metals. Many detection methods are available. For example, when measuring transition metals, a single column method can be used directly with conductivity or pulsed amperometric detectors, or post-column derivatization can be used to react metal ions with PAR or other color reagents, and then UV / VIS detection. The general rule is: for acids and bases without ultraviolet or visible absorption and strong dissociation, it is best to use a conductivity detector; for ions with electrochemical activity and weak dissociation, it is best to use an amperometric detector; for the ions themselves or after passing through the column The complex formed after the reaction has ions and compounds that absorb or produce fluorescence in the ultraviolet, and it is best to use a UV / VIS or fluorescence detector. If there are several options for the problem to be solved, the determination of the analysis plan is mainly determined by the type of substrate, the selectivity, the complexity of the process, and whether it is economical. Tables 1 and 2 summarize the separation and detection methods available for various types of ions. The development of ion chromatography column packing has promoted the rapid development of ion chromatography applications, and has provided many possibilities for the development of various ion analysis methods. In particular, the commercialization of hydrophilic, high-efficiency, high-capacity column packings in aqueous solutions of pH 0-14 and 100% organic solvents (organic solvents for reversed-phase high-performance liquid chromatography) makes the application of ion exchange separation even more expand. Common ions in the form of ions in aqueous solution, including inorganic and organic ions, with weak acid salts (Na2CO3 / NaHCO3, KOH, NaOH) or strong acids (H2SO4, methanesulfonic acid, HNO3, HCl) as the mobile phase, anions Exchange or cation exchange separation, conductivity detection, is already a mature method, there are mature chromatographic conditions can refer to. For near-neutral water-soluble organic "large" molecules (relatively common to small molecules), if the compound to be tested is a weak acid, the weak acid will exist as an anion in a strong alkaline solution, so it is stronger The base is the mobile phase and is separated by anion exchange; if the compound to be tested is a weak base, since it will exist as a cation in a strong acid solution, a stronger acid is used as the mobile phase for cation exchange separation; if the ion to be tested is hydrophobic Stronger, due to the adsorption between the stationary phase and longer retention time or peak tailing, you can add an appropriate amount of organic solvent to the mobile phase to weaken the adsorption, shorten the retention time, improve peak shape and selectivity. Ion-pair chromatography can also be used for the separation of these compounds, but the mobile phase generally contains more complex ion-pair reagents. In addition, high-capacity columns and weak eluents can be selected for weakly retained ions to enhance retention, and vice versa for strongly retained ions. There are two main detectors commonly used in ion chromatography: electrochemical detectors (including conductivity and amperage) and optical detectors. The ions that exist in the form of ions in the aqueous solution, that is, strong acids or alkalis, should be selected for conductivity detection. For compounds that have absorbing groups for ultraviolet or visible light or after post-column derivatization (less pre-column derivatization is used in ICs) to generate light-absorbing groups, use optical detectors. Compounds with oxidation or reduction reaction groups under applied voltage can be detected by DC ampere or pulse ampere. For some complex samples, in order to get more information in one injection, two or three detectors can be used in series. 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