Talk:Ion chromatography (IC)
Author: Hans-Jürgen Schwarz
back to Analysis of Salts
Abridged version[edit]
In general chromatography denotes a method for the separation of substances. These substances are distributed between a stationary and a mobile phase. A column packing of Al2O3, activated carbon, ion exchanger, etc. or a piece of filter paper may be used as stationary phase. The mixture to be separated, i.e. the mobile phase, is either liquid (e.g. paper chromatography, ion exchange chromatography) or gaseous (gas chromatography). The surprisingly high separation efficiency of this relatively simple method is based on a times 100– 10000 repetition of single separation operations during the passage on the stationary phase. In order to achieve the separation of chemically similar substances by chromatography, the partition coefficients of the two materials on the stationary phase have to differ at least slightly.
In the broadest sense, ion chromatography includes ion-exchange chromatography, ion exclusion chromatography, ion interaction chromatography (previously ion pair chromatography) and ion suppression chromatography.
Usually, the ion exchange chromatography is used for the detection of salt-forming ions[1]. In general, an exchanger’s affinity for an oppositely charged sample ion is greater, the higher the charge and the smaller the sample ion’s surrounding solvation molecules are. Furthermore, the affinity increases with the polarizability of the ions.
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The retention times <ref>the time required by the analyte for passing through the column, from injection to detectionCite error: The opening <ref> tag is malformed or has a bad name of the alkali and alkaline earth metals rise consequentially from lithium to cesium and magnesium to barium, because the polarizability of ions rises in the same direction, while the solvation ability rises in opposite directions. The same applies to halogen ions from flourine to iodine. For other ions, the situation is not so clear. However, the bi- or higher valent ions elute after the monovalent ions. Protons and hydroxyl ions have a large hydrate shell and therefore only a low elution strength. Retention behavior and selectivity of the separation are mainly influenced by pH- value, buffer <ref>acid-base pair that does not change in pH, when an acid or base is addedCite error: The opening <ref> tag is malformed or has a bad name, eluent ion<ref>carrier liquid or mobile phase of a gas<re/>, organic solvent additive or addition? (Lösungsmittelzusatz), and particularly heavy metals due to complexing agents.
The detector of choice for ion chromatography is the conductivity detector. Yet, in some cases other detectors provide good services.
Advantage:
The ion chromatography can be used for the analysis of cations and anions. However, it is mostly used for detecting anions, because there are better methods for the detection of cations. Ion chromatography provides accurate quantitative analyses.
Disadvantage:
Only ions can be determined, complete salt-phases are determined by deduction, which is only possible for simple systems.
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