Dear chromatographers,
I'm working in R&D division of nutraceutical company and planning to buy a new HPLC system with PDA for both QC work and semi-preparative separation of compounds from natural product (using 20~30mm ID column)
To meet my need, I presume that the system should have flow rate from 1 to >50ml with almost same flow rate & proportioning precision in that flow rate range. I¡¯m worrying about if the system with that flow range could come up with (or at least not so worse than) performance of analytical system (max flow rate 10ml) at flow rate of 1~2ml. I¡¯ve contacted 3 vendors and all of them guaranteed their systems for my need. but I would like to have some feedback from fellow users.
And, which mixer type would you recommend for my need? I¡¯m referring old conversations about HPG vs LPG and expect up to date opinions on this matter.

Thank you.

ps. if you have complete list of HPLC brands, please post here or e-mail me

ps again... I'm interested in 3 models, Waters Delta600, Dionex and JASCO with semi-prep pump module. please let me know if you have any opinion on these specific models or recommend any other systems which are good for my need.
thanks a lot

You will probably find that any of these LC's will perform well in the semi-prep mode. You also will probably find that they do not perform so well in the analytical mode. To get the higher flow rates, you need to use larger and larger internal diameter tubing, flow cell tubing, shorter path length in the flow cell, and larger pistons and check valves. Dead volume will decrease the resolution and increase the tailing in the analytical scale mode. The shorter path length in the detector will give reduced responses in the analytical mode. Typically, IMO, you really need two separate systems to properly do what you want to do at the flow range you desire.