The Quest for a Universal Chromatography Technique
LC, GC, UPC²: Why can’t we analyze everything with one technique?
One of the Holy Grails in chromatography seems to be the quest for the universal technique — one that can cover “all” compounds.
While there have been many advances in both separation (e.g., HPLC, UPLC, UPC²) and ionization techniques (e.g., UniSpray) there is still nothing that can cover the entire range of compounds encountered by a modern analytical laboratory.
Who knows what future innovations might be around the corner, but one question to ask would be… with technology as it stands, why can’t we analyze everything with one technique?
When considering that the range of compounds that might be subject to chromatography goes from highly volatile species with molecular weights of tens of Daltons, to proteins with molecular weights of hundreds of thousands of Daltons, maybe it isn’t so surprising that there are a variety of techniques required.
The two dominant techniques are liquid chromatography (LC) and gas chromatography (GC). Deciding which one to use is based on several physiochemical properties, primarily polarity, but also molecular weight, temperature stability, and solubility. As a rule of thumb, low molecular weight and (relatively) non-polar molecules tend to suit GC/MS, whereas relatively polar and larger molecular weight molecules tend to suit LC-MS.
There is always, of course, exception to this rule. There is a grey area of compounds and separations that may work on both LC and GC with varying degrees of performance. A good example is the analysis of pesticides, of which there are hundreds in use worldwide. The analytical method must be chosen carefully to make sure any regulatory limits are achieved, considering that there may well be some compromise.
Another thing to consider is if the analysis is directed at known components (targeted) or unknown components (untargeted).
- If it is a targeted analysis, although the aforementioned decision and possible compromise is still there, a known list of compounds can be cross-checked with existing methods, or at least theoretical calculations.
- When creating an untargeted analysis the analyst must ensure there the entire, or at least a representative amount, of components are analyzed.
With emerging techniques such as exposomics, full characterization of the exposome at the research stage is crucial. A broad-brush approach may therefore be the best option in this case.
One possible solution, in the absence of a truly universal technique, is the option to run liquid and gas chromatography on a single analytical platform. This has advantages from a hardware point of view, where a high capital investment is involved and flexibility and future-proofing is a consideration. Also, a common data system and informatics can make data processing and interpretation much simpler.
As much as we live in the age of rapid technological advancement a universal chromatographic technique is still not a reality. It’s always good to have high aspirations to motivate and inspire new technology and hardware innovations, something Waters has at the heart of our ethos.
One approach to get around these limitations is to use a flexible analytical platform, Waters has a range of separation and ionization techniques to enable full characterization of even the most diverse and complex samples.