PACKING MATERIALS FOR ENANTIOSELECTIVE PREPARATIVE CHROMATOGRAPHY

This paper considers the application of chiral stationary phases to pr eparative liquid chromatography. The various types of CSPs are briefly reviewed in terms of their loading capacity, structure and general ar eas of application. Enantioselective preparative separations display c ertain aspects not necessarily encountered in more conventional achira l applications. These specifically involve the solubility of the targe t molecules in the mobile phases conventionally used in enantioselecti ve chromatography. Strategies for the development of separations using mobile phases more suited to the requirements of preparative chromato graphy are outlined, with special reference to the use of carbohydrate -based CSPs. Since the selectivity is the most important, parameter in determining the usefulness of a particular set of separation conditio ns for preparative application, attention is also give to the optimisa tion of mobile, phase selectivity by variation of the nature of the so lvent and also of the acidic or basic additives which may be used in t he case of the separation of ionogenic solutes under ''normal phase'' conditions. In the scale-up of preparative separations to production s cale, which is becoming of increasing importance of chiral pharmaceuti cal products and intermediates, an often misunderstood parameter is th at of the influence of particle diameter, especially in the case of a SMB chromatography. The influence of particle size on the economics of large scale purifications is discussed and it is shown that, in contr ast to the case of achiral separations where there is an economically optimum particle size, the particle diameter used for preparative enan tioselective separations, even SMB, should be the smallest possible co nsistent with good column performance.