Tuesday, March 25, 2008
Let's talk about TLCs Part 3 - Phosphomolybdic Acid (PMA) Stain
PMA Stain is a highly versatile general stain for developing TLC plates. The stain is easily prepared by dissolving 10 wt. % phosphomolybdic acid in ethanol. More PMA can be used however as stains go PMA is relatively expensive.
TLCs developed with PMA stain upon heating give green/dark green/dark blue spots on a yellow/green background (see picture).
Phosphomolydic acid (PMA) Stain Recipe
100 ml container
100 ml Ethanol
10 g Phosphomolybdic acid, H3[P(Mo3O10)4] · xH2O
Alternatively, you can go for the more expensive solution and buy ready made PMA stain from Aldrich (see picture). Where I've worked in the past we simply poured some of the ready made stuff into a jar and use it for our TLC plates. At the end of the day we poured it back into the Aldrich flask and rinsed with some ethanol. Using this method the stain lasts for a very long time. I never had any problems storing the stain at room temperature despite Aldrich's recommendation to refrigerate.
See under Vanilin Stain for general staining guidelines. D!