Chromatography Forum

Hello all,

I have to promote HPLC to my students.
Actually they are a little bit frightened about HPLC and are using TLC a lot.
Could you give me some advantages and inconvenient ?

HPLC (UV-PDA) :

Beter sensibility
Beter selectivity
Quantification of analytes
Speed (i generally use IS column in reverse phase)
Possibility to use elution gradient


TLC

Easy to use
$ cheaper chromatography

Thanks,

Laurent

Advantages of TLC

Easy to run multiple samples in parallel (which can cancel out the speed of HPLC)

Huge range of "post column" derivatizations that can be very selective.

Straightforward 2D

Permanent archiving of actual separations may be possible

As long as the solvent front does not reach the top of the plate the analyte must be on there somewhere; in HPLC it is either stuck on the inlet frit or dissolved in the waste bottle !

Peter

Down scaling and up scaling is possible with HPLC, micro HPLC is more sensitive, UHPLC is faster than TLC, pre and post column derivatization is possible with HPLC, different detectors can be used with HPLC, coupling with MS, MS/MS or NMR is possible with HPLC, results are more precise than with TLC.
In TLC screening is faster and cheaper, coupling technics are more difficult and at the end more time consuming.

Both technics should be used, but finally HPLC is the separation technic of the art, and should be prefered. Later, when your studends are going to industry, or into research, HPLC knowledge is required.

Make them separate something extremely tedious that involves spotting 100+ TLC plates. Worked for me!

You could produce a generation of students here who have realised that HPLC stands for Highly Pricey Liquid Chromatography, and that TLC is sometimes worth consideration.

Sometimes I feel that the two primary reasons behind most people's choice of analytical approach is (a) I know how this one works; (b) I have the right kit. TLC suffers from not looking complicated enough, but it's a valuable technique. Where possible, I'd rather run radioactive samples by TLC than decontaminate an hplc.

Dear Laurent,

why do your students prefer to use TLC?

each techniques has it's pros and cons and complete each other in a way but they do not need to compete to each other.
it all depends upon your needs

for example:
an organic chemist will use TLC first to find quickly a method for fast and "dirty" flash method to get a good 90-95% clean product from their synthesis,
after flash clean up on a glass column or flash instrument they will always use TLC to quick see separation of fractions and HPLC to determine % purity and also yield.

Will using HPLC bring a certain added value for them in term of results and efficiency? if it does then simply showing it to them will make them want to use,
one example that i remember is the move to flash instruments, simply because wasting your life in front of a glass column versus a 15-30 min.
I remember one professor saying one time, if I buy such an instrument what will my MSc students do for 2 years
and the answer in the end was they can do 4-5 times more in term of research

Despite its apparent simplicity, TLC is actually a *very* complex technique because it occurs under non-equilibrium conditions (dry -> wet). The stronger solvents in the mobile phase are preferentially sorbed to the stationary phase so that almost all TLC separations are actually run under what would be "gradient" conditions in HPLC. Now, imagine having to develop a gradient HPLC method where you had no direct control over the steepness of the gradient and no direct control over the flow rate.

Add to that the complexities of quantitation by reflectance.

That's not to say that TLC doesn't have its advantages (peter laid them out very nicely). I'll try to do as well for HPLC:
- easier, more reliable quantitation (radioactivity is the exception here)
- more reproducible results, less variability with environmental conditions
- more amenable to automation.

When all is said and done, I'm a "Darwinian" as far as technology goes; when you see one technique that dominates, that's usually because it has a net advantage over competing techniques.

Thanks to all for your usefull comments !

I'll expose to them advantages of each technic.
Having work for 10 years in industry before university, i think that they have to know as much as possible how HPLC is working.

Just to show I'm not biased .....

HPLC has more resolution (with all the usual caveats)

Peter

One important thing doesn´t seem to have been mentioned: HPLC allows the analysis of more volatile substances (which would evaporate from the TLC plate).
Still I am one of those who is completely convinced that both methods have their place.
Also, the "Darwinian" aspect is often just a fashion.

Also, there is HPTLC which is equivalent to HPLC, but I think it depends on the availability of needs... i.e. a certain compound can be analyzed by both techniques but may need a certain type of column u don't have, so u will apply TLC ....
and both really gave good results....
best regards