Chromatography Forum

This is my first post on this forum and in fact I am very new to the field of research so I might seem a little lost...my apologies for that.
well, I am working with crude plant extracts and plan to study their bioactive compounds in detail, for which the first step i suppose is to separate and isolate the various phytochemicals...so i am planning to initially go for analytical TLC followed by HPLC. However, I do not know on what basis I should select my solvent system for TLC. I am more interested in isolating the alkaloids, flavanoids and tannins from the crude extracts so kindly suggest the best solvent system for that. Also, because I am from a non chemistry background, i will be grateful if you can suggest some books/journals which i can refer to in regard to the chromatographic techniques used in separation of natural products in particular plant phytochemicals.

Thank You.

there's no "best" system for plants. It depends on the plants constituents.
So you have to find the one that fits your purposes.


But some suggestions for Literature:

beside the generic basic books about chromatography these sources could be of special interest for you:

Preparative chromatography techniques - Applications in Natural Product Isolation
Kurt Hostettmann, 1997, 2nd Ed., Springer, ISBN-13: 9783540624592

and some Journals:
- Phytochemical analysis
- Journal of Agricultural and Food chemistry
- Phytochemistry

Add Journal of Natural Products to Hollow's list.

For alkaloids, I used to partition the extract in dichloromethane/acidic water (1 N HCL). The alkaloids would be in the aqueous layer as a salt. I would make the water basic and partition again with dichloromethane, the alkaloids would move to the DCM which I evaporated and the compounds could be purified on C18.

Chromatographically, I've written an application note describing the isolation of alkaloids using a strong ion exchange column- found here: http://www.isco.com/WebProductFiles/App ... olumns.pdf

For flavanoids, a similar procedure could be followed with a strong anion exchange column; I've written an application where I've isolated flavones with this technique; it should be posted soon. Send an e-mail to jsilver teledyne.com and I'll send the word file to you. Here's an application note describing other flavanoid methods: http://www.isco.com/WebProductFiles/App ... pounds.pdf

I found tannins to be difficult to work with. I think the SAX column might work, using a diol column as aqueous normal phase might also work.

I work with tannins on a daily basis. Diol will work for proanthocyanidins (a.k.a. condensed tannins). Run a gradient of acidified MeOH into ACN. Methinks retention is mostly based on H-bonding. As such, elution is dependent upon degree of polymerization or more correctly, degree of hydroxylation. Keep in mind that all diol phases are not created equally. Details of separation upon request.