Wednesday, December 7, 2011

Process Wednesday: TLC

One thing that I love about Organic Process Research and Development is the editorials by Trevor Laird. I suspect that Dr. Laird has been proto-chemblogging since 2000 or so. A bit of a gem on the organic chemist's favorite bench-scale analytical technique [1]:
I had finished my Ph.D. in 1970 and worked for many years in industry before the technique of HPLC became routinely used: first, in the analytical laboratory and subsequently by process chemists as a tool for following reactions as well as analysing products. I still remember the days when TLC was used, not just for qualitative analysis but also for accurate quantitative analysis of finished APIs. It is still useds in its HPTLC modes by some companies, particularly in Germany, as an accurate quantitative method of analysis, but the technique has been forgotten as a quantitative method by many younger chemists.  
TLC has some major advantages over HPLCs -- cost being an important one. This means that it can be used in all circumstances, such as on the manufacturing plant. Since it is simple to use, process operators can easily perform the technique accurately. The second major advantage is that you see everything -- if you use correct visualisation (spraying and heating as well as UV visualisation) whereas with HPLC it is possible for impurities either to be retained on the column or to be late eluters which impatient organic chemists, but hopefully not analysts, might miss. 
On a consultancy project in which I was recently involved, TLC was the only way in which a particular impurity could be detected and quantified. It is a useful adjunct -- or a reality check -- to HPLC in many instances. 
[snip] So those of you who have abandoned TLC -- particularly quantitative TLC -- in favour of only HPLC, remember that TLC also can mean: The Lowest Cost.
I'm intrigued by the concept of having process operators perform TLC in the manufacturing plant; I think it's doable, but I think it would take a good bit of training to have relatively new operators correctly interpret TLCs. 

1. Laird, T. Org. Process. Res. Dev. 2006, 10, 1. 

1 comment:

  1. We often used TLC in the pilot plant and production. The operators were always interested and grasped the concept quickly. It saved time and money. We had several SOPs in position and the only thing they needed to verify was the solvent composition, which was quickly done by GC, in the production or pilot plant labs.