Chromatography Forum

Hi,

I am fresh in prep analysis and find myself caught in the midst between semi prep and prep HPLC analysis.

My questions are:
1. what is the different between semi prep and prep analysis?
2. what are the parts that need to be changed in HPLC instrument when scaling up from analytical to semi prep and prep analysis?

Thanks in advance.

Semiprep is normally up to 20 mm column I.D.(internal diameter)
more than 20 mm column I.D. = (normal) prep.

A (semi)prep system has to deliver higher flow rates ( for 20mm column: 20 ml/min), the detector has to be less sensitive in order to cut the peaks not at high concentrations, and maybe, you want to have a fraction collector to collect the purified substances. There are some special needs for the controlling software, like real-time controlling, too, but this isnt a must.

Best regards
Chris

PS.: prep analysis is no good word, because in prep , you dont want to analyse, you want to purify.

Just to amplify a bit. You don't usually need a new detector, just replace the flow cell with the "prep" version. It will have a short pathlength to deal with highly concentrated peaks and wide capillaries to permit high flow rates.

My questions are:
1. what is the different between semi prep and prep analysis?
2. what are the parts that need to be changed in HPLC instrument when scaling up from analytical to semi prep and prep analysis?

Whilst agreeing that 20 mm diameter is one defining boundary between the two, semi-prep can often be performed on simply-modified, or unmodified, analytical HPLC systems, whereas preparative usually requires more extensive modfications to pump, lines, and injectors.

You don't have to change the detector, you can put a simple flow splitter after the column so that flows to detectors are the same as for analytical systems.

Just to maintain the same linear velocity of 1 ml/min on a 4.6mm internal diameter analytical column, a 10 mm diameter column requires 5 ml/min, a 21mm diameter requires 21 ml/min, a 30 mm diameter column requires 42 ml/min, and a 50mm diameter column requires 118 ml/min.

As a simple guide, the amount of material that you want to purify increases by the same ratio, if other parameters are similar ( column length, packing, particle size etc. ). There are separate scale up equations for flow and load, but preparative systems can work with recycle at overload conditions, so load quantities can vary according to the separation.

The preparative systems usually have larger sample injection loops ( up to 20 ml ), pumps that can handle 100ml/min ( if you want a full binary gradient at 100 ml/min then two 100 ml/min pumps are used ),
larger diameter lines, etc.

One issue with preparative systems can be removal of the solvent from samples. It's possible that removing the larger volume of solvent from larger sample masses exposes sensitive samples to temperatures for longer, and degradtion occurs.

Some HPLC manfacturers have analytical systems that handle semi-prep ( up to 20-30 ml/min maxium flows, but others sell systems with only 5 or 10 ml/min maximum flow, as they minimise system volume to optimise analytical resolution. They usually offer separate preparative systems, but about the only interchangeable parts may the the injector ( 1 - 2 ml ) and detector ( with splitter). Water baths make suitable prepartive column ovens.

Bruce Hamilton