I am looking in purchasing a prep system to do compound isolation and purification from crude plant extracts, since many of the compounds I require are not available commercially. What I was wondering was, with developed HPLC analysis conditions, would compound isolation on prep system take much time? I do not have much experience in this area and I am wondering if mobile phase development is the most time consuming element or is most of the hard work done,if you already have a specific HPLC method developed.
I understand that this procedure will be dependant on the complexity of the extract, but have you any rough guideline for me on time required? Say for relatively for simple extracts?
Any help would be appreciated. Thank you.

Hi, Anonymous
I have not direct experience in the field of preparative chromatography but I have reviewed some system for purification step in environmental analysis.
OPLC (OverPressure Layer Chromatogrphy or Optimum Performance Laminar Chromatography) is an interesting and promising technique for preparative and purification purposes.
See details at www.bionisis.com
Good Luck

The correct answer is: It all depends. It's not very precise.
Things to consider are: compound concetration, compound properties, detectability, matrix, solubility.
Often it is easier and faster to use other techniques, such as liquid/liquid partitition, alkaloid workup, specific extraction, open column normal phase chromatography etc.
I once had to isolate a compound from dryed plant material. I did use two liquid/liquid partitition steps (one to remove unpolar stuff like fat, chlorophyll etc. and one for polar stuff like sugars etc), normal phase open column chromatography and as a last step prep. HPLC. Yield was 40 mg from 2 kg plant material - still 80% of my compound. Unfortunately the vial containing the majority of the substance was smashed by postal service when send to in-vivo testing.
However, in other cases re-crystallisation was sufficient.

I assume that you have an MS or standards to identify the elution times of the compounds that you are after. Then all you need to do is to run gradient chromatograms and collect the samples. This gives you a first cut at the compounds, albeit not necessarily pure samples. Further purification can be obtained by submitting the collected samples to an orthogonal HPLC step, or other more classical means of purification.

The main drawback of any chromatographic procedure is throughput. The sample load that you can apply is low, even with the best techniques like at-column dilution and maximizing load with the charge-state of the compounds. 10 to 30 mg per g of packing is a reasonably high load.

I agree with the last post that preliminary prefractionation techniques are important before prep HPLC.