Chromatography is an exceptionally popular tool that is used every day in laboratories around the world for the analysis of chemical mixtures by the separation of unique chemicals through interactions between the molecules and the material that is permanently bonded to the chromatography column’s packing material.
Separation happens when chemicals have different strengths of interaction with the packing material as they are pushed through the chromatography column by a solvent, usually a mixture of water and a polar liquid chemical like methanol or acetonitrile.
When one chromatography column and solvent system is used there is a single type of chemical interaction that governs how strong these interactions are and the type of separation that is achieved. These include the chemical’s hydrophobicity (preference to be in a non-polar environment), polarity, shape, size, or other chemical properties. However, sometimes there are cases where a single type of interaction is insufficient to separate a complex chemical mixture and additional factors are required.
Multidimensional chromatography is an analytical tool takes advantage of two (or more) unique chemical properties to evoke separations in multiple dimensions. This provides the scientist with the potential of much more information about the nature of their samples through the distinction between chemical similar materials. There is also potential for multidimensional chromatography to separate a greater number of unique chemicals (as opposed to partial separation or coelution).
In the video below, the ‘chemical’ mixture consists of components of different shapes and colours. Before the separation all the chemicals are mixed together. The scientist wants to know how many chemicals there are and what is their shape and colour. When the plate is dipped in the first beaker the solvent mobile phase is selective to the shape of the chemical; the separation occurs based on shape to the exclusion of all other properties. This is analogous to a one-dimensional chromatographic separation. The plate is rotated and placed in the second dimension that is selective to the chemicals colour thereby completely separating these 5 chemicals that can now be identified and quantified.
Why is multidimensional chromatography important? Metabolomics is an example of current medical research that needs information rich analytical tools to take a snapshot of the chemical composition of a biological system. This can be used to find chemical markers that distinguish between health and disease/cancer state individuals. Untargeted experiments are commonly done by scientists to find these marker molecules and multidimensional techniques can give the researcher the needed analytical power. Mathematical and statistical analyses are then used to identify the key markers that inform on a patient’s medical state through modelling and predictive tools.
Header image credit Oliver Jones, RMIT University
Paul G Stevenson 