Liquid Phase Ion Chromatography (IC) allows the identification and simultaneous quantification of various inorganic and organic ions (cations and anions). The principle of this technique is based on the differences in ion affinities for a functionalized substrate (ion exchange resin) in the presence of a carrier liquid phase (eluent).
In practice, a few milliliters of sample previously dissolved by appropriate techniques are injected through a column containing the ion exchange resin.
A continuous flow of eluent is applied to the exchange column. As the eluent passes through it, the ions in solution are adsorbed on the surface of the resin in proportion to their selective affinity and according to the composition of the eluent. An advancement front is formed in the column for each ion which is late with respect to the advancement of the carrier phase. The different ions in solution will thus have been separated at the outlet of the column.The detection of eluted ions is carried out by conductimetry or by UV spectrophotometry. The assay of the ions requires a calibration which consists in precisely determining the elution time and the area of the peak associated with the advancement front of each ion present in reference solutions.
There are two ways to use ion chromatography on the platform. The isocratic mode which corresponds to an analysis with 100% of the same eluent all along it. With this method, we measure anions (chloride, nitrate, sulfate) or cations (sodium, potassium, ammonium, magnesium and calcium). In this specific case, the detected concentrations are between 0.1 and 30 ppm.
The second mode is the gradient that is to say that the analysis undergoes a variation in the concentration of the constituents of the eluent mixture lasting over time. Only fluoride, chloride, nitrite, sulfate, nitrate and phosphate anions can be measured and in the range of 0.5 to 100 ppm.
Applications of this technique:
- Anion measurement: F-, Cl-, SO42-, NO2-, NO3-, PO43-
- Measurement of cations: Ca2+, Na+, NH4+, K+, Mg2+, Al+, Fe2+/3+…
- Sugar dosage
- Determination of organic acids