If you’re in the field of metabolomics then ion chromatography (IC) probably isn’t a technique at the forefront of your mind. However many metabolites in the citric acid and glycolysis cycles are ionic and find themselves perfectly suited to separation by IC. Whilst there is some overlap in compounds that can be run by high performance liquid chromatography (HPLC) and hydrophilic interaction liquid chromatographic (HILIC), organic acids, sugars and purines and pyrimidines are no strangers to IC, so would it not make more sense to use a technique that is specifically designed for these compounds?
The odd couple?
Ion chromatography provides a direct separation for ionic species, no derivatisation required, with excellent selectivity and sensitivity. IC is also a perfect partner for your mass spectrometer. The suppressor device required to neutralize the background from the eluents and remove counter ions, convert all of the salts into water – meaning the output of the IC is your ions of interest in water – which makes a more mass spectrometry (MS)-friendly output than corrosive salts. Additionally, the suppressor converts all the analyte ions into a single hydronium or hydroxide form. This leads to higher ionization efficiency and greater reproducibility even in the face of varying sample matrices. In a previous blog post the question was asked “Can a mass spectrometrist be comfortable with ion chromatography?” Many of the concerns over using IC with MS are addressed in this blog post and as the demand for IC-MS has increased, the practicalities of coupling the two together have been ironed out so the coupling is as simple and effective as possible.
This application note on the untargeted metabolomics profiling of oral cancer cells discusses the technique in a practical sense and makes comparisons to HILIC and capillary electrophoresis as alternatives.
What’s in your tool box?
Of course Ion Chromatography can’t give you all the answers. No one technique truly can. However it is an essential tool to partner your LC-MS analysis. It can fill in the gaps that HPLC separations leave open and help to complete the whole picture. It would be like filling in a crossword puzzle with only 80% of the clues or a jigsaw puzzle with pieces missing. You may be able to guesstimate the missing parts by applying some logic, but you can never have full confidence unless you have all the clues at hand. A full arsenal of reverse phase and HILIC HPLC-MS methods AND IC-MS makes for the sharpest tools in the box. This is why Thermo Scientific supports switching an MS detector between LC and IC front ends.
Like what you are learning?
If you would like to learn more on IC-MS we have an educational webinar available to listen to.
In English language: Ionic Metabolites – A challenge for IC-MS?
In German language: Ionische Metabolite: Eine Herausforderung für die IC-MS?