IC - Ion Chromatography
Columns for the analysis of anions and cations
IC SI-36 4D
IC SI-37 4D (new!)
Anion analysis for suppressor methods
Quaternary ammonium groups
Polyvinyl alcohol particles
3.5 µm particle size
Good separation of sulfite ion / sulfate ion
Analysis of seven general inorganic anions within 30 minutes under isocratic conditions
for NaOH or KOH eluent
Theory about Ion Chromatography
Ion chromatography, one form of liquid chromatography, separates and quantifies inorganic anions and cations, organic acids, organic bases, and a variety of other ions. Separation mechanisms including ion-exchange, ion-exclusion, and ion-pair chromatography are used.
In ion-exchange chromatography, electrostatic interactions resulting from Coulomb forces are used to separate counterions on ion exchange resin. Using anion analysis as an example, below figure presents the principles of ion chromatography.
Prior to sample injection, anions in the mobile phase (eluent) are retained by the modified functional groups (cations).
While moving through the column, eluent anions continuously compete with each other (a process known as ion exchange) [Figure 2-1(1)].
Once injected, the sample anions displace the eluent anions and are retained by the functional groups [Figure 2-1(2)].
Moving through the column, the sample anions compete with the eluent anions and are eventually eluted from the column [Figure 2-1(3)].
An ion with a larger charge and smaller hydrate ionic radii experiences stronger retention by the ion exchange resin.
A conductivity detector is generally used for ion analysis because ions are excellent conductors. Current flows when a voltage is applied across two electrodes immersed in an ionic solution. Conductivity refers to the capacity of an electrolyte to conduct current. The concentration of ions can be determined by comparing the conductivity to that of a standard sample of known concentration of target ions. Ion chromatography employs an electrolytic solution as an eluent, which means that the eluent itself also exhibits conductivity. Eluent with high conductivity (i.e., background conductivity) results in high background noise and consequently decreases sensitivity. There are two methodologies of electrical conductivity detection. Suppressed conductivity method removes counter ions of the eluent after separation, thus reduces background noise. The other methodology, non-suppressed conductivity detection, uses a low-conductivity eluent instead.
There are two types of Ion Chromatography methods: The suppressor method and non-suppressor method.
Shodex carries columns suitable for both types. As the name tells, the suppressor method uses a suppressor which removes ions that interfere with analytes measurement. The suppressor system is expensive, but some say the sensitivity of suppressor method is superior to non-suppressor method. In contrast, system required for non-suppressor method is cheaper, but the useable solvent is limited to the ones with low conductivity such as phthalic acid.
Suppressor Type Ion Chromatography Column
Shodex IC SI-90 and SI-50 are the suppressor type anion chromatography columns. SI-50 is the higher performance type of SI-90. SI-52 is another suppressor type column suitable for the separation of oxyhalides.
For rapid analysis there is the IC SI-35 4D and IC SI-35 2B with smaller column dimension and particle size of 3.5 µm.
There is the IC SI-36 4D and the new Shodex column IC SI-37 4D with higher performance for oxyhalides.
Non-Suppressor Type Ion Chromatography Column
Shodex IC I-524A and NI-424 are the non-suppressor type anion chromatography columns. NI-424 is the higher performance type of I-524A.
Shodex IC YK-421 and YS-50 are the non-suppressor type cation chromatography columns. YS-50 is the higher performance type of YK-421. They can separate both monovalent and divarent cations simultaneously.