Sometimes life is not easy with two choices only, and neither of them fit to your expectations or needs…
In chromatography, between HPLC and GC, there is a unknown Third Way : HPTLC.
HPTLC stands for High Performance Thin Layer Chromatography and appeared in the 70’s as a technical and methodological improvement of TLC. The “old TLC” is now more than 75 years old, and it is time to replace it by a relatively newer method. Until now, HPTLC grew in the shadow of more fashioned liquid chromatography, HPLC then UHPLC. But HPTLC, which is a liquid chromatography too, is easier to couple with any other method, especially for detection . This wide detection range enables to get both identification and quantification. High sample amounts may be evaporated during spray-on sample application which helps to get a high sensitivity.
The focus will be given on the current features of the method, and on when it might be the method of choice.
Recent improvement of MS detection on plates increases the interest of HPTLC. And the detection of activity directly on the plate ( EDA for effect directed analysis ) is also a very powerful tool, including for example the detection of an anti fungal or of an antibiotic against Staph. Aureus or of an unknown endocrine disruptive, down to the fg level, directly on the plate.
These capabilities of HPTLC are finally due to the fact that after separation, the complete sample does not go to the waste, but remains accessible on the plate, for further evaluation.
The compatibility with biological matrix has very few limitations on a plate, especially regarding single use of the plate separation medium.
There is less risk on the plate to miss any sample compound, as all sample is accessible, and the range type of detection is much wider, as including chemical staining and “bio-detection”.
It is faster due to parallel separations with up to more than 50 analyses on a single HPTLC 20x10 plate, and due to instant start as neither prior rinsing nor column equilibrium is needed on plates. This analytical speed to find a new compound having the expected properties helps the speed of the drug discovery.
As time is money, and as HPTLC requires a very little solvent consumption only, it is a cheap method.
As any method, HPTLC has of course limitations, which are actually the miss of knowledge about it.
The next International Symposium for HPTLC will take place next time in Berlin, Germany, 5-8th July 2017. (www.hptlc.com), will be a way to compensate this weakness, and to a lesser extent, this contribution too.
Literature:  G. Morlock, W. Schwack, JCA 1217 (2010) 6600-6609.