16
November/December 2009
Applications of Liquid-Liquid Chromatography Instrumentation for Laboratory Preparative & Process Chemistry
Brown, Leslie & Luu, Trinh Anh of AECS-QuikPrep Ltd, PO Box 80, Bridgend, S. Wales, UK. CF31 4XZ (
aecs@gmx.com ) Author for correspondence Hill, Colin & Flockhart, Ian of Botanical Developments Ltd, of UK Garret, Pierre-Henri & Margraff, Rodolph of ETS-Couturier, of France Skouroumounis, George of University of Adelaide, of Australia
Liquid-Liquid Chromatography instrumentation (L-LC), also referred to as Counter Current Chromatography (CCC), and Centrifugal Partition Chromatography (CPC), design has been instigated and, championed largely by Academics at University and Research Institutes in USA, Japan, Europe and China. To date instrumental L-LC has not been universally adopted by chromatographers in many commercial sectors. Discussed is a scientific treatise from a commercial viewpoint, of usage and design advantages and disadvantages of instrumental L-LC.
Keywords: Liquid-Liquid Chromatography, Counter Current / Countercurrent Chromatography, Centrifugal Partition Chromatography, Laboratory / Process Chromatography, High Throughput / Combinatorial Preparation.
Introduction There are very many fundamentally different modes of L-LC instrumentation design. The two major design modes in present use are planetary centrifuges (usually referred to as CCC, HSCCC or HPCCC) and sun centrifuges (often referred to as sun or droplet CPC), Recently the International CCC Committee voted to define planetary CCC as hydrodynamic CCC, and sun or droplet CPC as hydrostatic CCC, whilst acknowledging that both are Centrifugal Partition Chromatographs (CPC).
The industry wide use of CCC nomenclature has lead to much confusion in the mode of operation, as to non L-LC chromatographers; Counter Current modes would involve two liquids moving in different directions. With L-LC/CCC despite the fact they can readily be used with liquids moving in two opposing directions, in reality over 99.9+% of usage cases, only one phase is stationary and one phase is mobile. For this reason we have chosen to refer to this science as L-LC rather than CCC or CPC. In this publication we will refer to planetary CCC, HSCCC and HPCCC as hydrodynamic L-LC and sun or droplet CPC as hydrostatic L-LC.
Solid Liquid Chromatography (S-LC) techniques would include Open Tubular, Flash, Medium Pressure Liquid Chromatography (MPLC) and High Pressure (Performance) Liquid Chromatography (HPLC).
In S-LC one phase is stationary and one phase mobile. The stationary phase is often an
immobilised liquid, which has been immobilised by bonding to a solid substrate. Liquid-Liquid Chromatography is therefore in many ways directly analogous to Solid Liquid Chromatography.
The main difference between L-LC and S-LC in many cases is L-LC maintains one of the pair of immiscible liquids stationary, through its physical mechanical/electrical instrument design, rather than adsorption onto a solid particle. Why then is not L-LC the equal scientifically/commercially of S-LC?
A Review of CCC/CPC Historic Confusions, To Enable L-LC Become Mainstream Chromatography
Confusion 1. Nomenclature. In the Introduction the major confusions associated with the nomenclature and mode of operation of CCC/CPC is discussed. We proposed in this paper, as we have for several years to the International CCC Committee, that consideration be given to more appropriate nomenclature.
Confusion 2. L-LC is a laboratory scale curiosity. Historically yes, now no.
Modern L-LC instrumentation can range from 7 ml for L-LC MS studies of trace amounts, to single units of 10 to 25 litres, or modular process units in any number/configuration of multiples of 3 litres capable of multiple tonnes/annum production. Research applications include natural products, nutriceuticals, agrochemicals, pharmaceuticals, and food/beverage etc. Large-
scale production (20 litre + units) is mainly limited to natural product based products.
Confusion 3. Different concepts of L-LC can interchange methodology. True on occasions, but still a misleading statement.
The reality is that the equivalence of different L-LC modes to other L-LC modes is not comparable in SLC to one manufacturer’s C18 or silica column to another’s C18 or silica respectively (although we all know significant differences can occur even in S-LC). It may not even be equivalent to comparing in chiral S- LC, a cellulose to an amylose carbamate. It could be more like comparing these to a Pirkle chiral column. The reality is, L-LC’s with fundamentally different design principles may do the same separation, but each might do in a radically different way. Transfer of method between two different L-LC design concepts with the same solvent, target and matrix, is as much luck as science.
The above can even be applied within a single manufacturer’s product range, if the manufacturer varies key L-LC design factors. The more factors they vary, the greater the likelihood of failure during Process Scale-up. Rationalisation of design by using modularity of design in both modern forms of L-LC instrumentation can reduce the problem of scale-up to make them no more difficult than in reverse phase S-LC.
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