Often, manufacturing isn’t finished when a product leaves the production line. Many products – for example, biomedical devices, electronics, and plastics– still have to be tested for cleanliness and contamination. And, sometimes, ion chromatography is the only technique that affords the necessary quantitative ionic cleanliness analysis.
Ion chromatography (IC), also called ion exchange chromatography, is a cleanliness-testing technique that involves the separation of anions or cations. This separation is accomplished through the use of high performance liquid chromatography (HPLC), which is based on the separation of the components of a mixture in solution by selective absorption. The ions in a sample are moved through the system by an ionic solution (eluent – the mobile phase), and then the various ions are separated in a column with an ion-exchange resin (stationary phase). The resin’s surface layer has limited ion-exchange sites that attract either anions or cations. A detector at the end of the column measures the quantity of exiting ions, and from this data a chromatogram is produced.
Steps in the IC analysis process:
- Sample preparation – The sample or components of interest must be suspended in solution. In many cases, a solid sample will be extracted with ultra-pure water to remove any ionic species present.
- Feed injection – The sample or water from the extraction of the sample is injected into the carrier fluid.
- Separation – Ionic separation of the sample takes place.
- Exiting of components – The components exit (elude) from the column, beginning with those least bound to the stationary phase. The time it takes for each species to pass through the system is unique to that species.
- Detection – The eluded components are analyzed by measuring the change in conductivity, UV absorbance or refractive index of the eluent as the separated ionic species pass through the detector.
- Chromatogram – A chromatogram is produced that plots the peaks representing sample components.
Generally, the IC testing, from set-up to final IC analysis, takes about an hour.
Additional applications of Ion Chromatography:
- Analysis of water for pollution and contaminants (both water for human consumption and aquatic ecosystems)
- Determining additive and sugar/salt content in foods
- Isolating selected proteins
The chief advantage of IC for separation of samples is that it is easy, fast, and sensitive, especially in detecting and plotting concentrations of inorganic anions and cations. And further development and improvement of this method is ongoing, with several new applications on the horizon.
IC testing can be an indispensable tool for cleanliness testing to ensure quality control: a tool that can be used to complete the manufacturing process before products ship to market. IC analysis is the only available technique that allows for quantitative analysis of anions and cations at the level of parts per billion (ppb).
Explore more about how ion chromatography can be used for environmental testing.