Large-scale separation of chiral drugs (a priority in the pharmaceutical industry) can be achieved with this method. In simulated moving bed chromatography (SMBC) 6-12 columns containing a CSP are joined in a ring and the fluid is circulated using 4-5 pumps. As the racemate travels through the columns a zone of one enantiomer leads the rest of the injected sample while a zone of the opposite enantiomer lags behind. Using a computer-controlled system, some of the leading enantiomer, and, independently, some of the trailing enantiomer are withdrawn at intervals. As polysaccharide-based columns have a high loading capacity they have been widely used for chiral SMBC separations of up to 1.5 kg of racemate per kilogram of CSP per day. SMBC has been applied for the separation of a number of chiral drugs and intermediates such as propranolol, analgesic tramadol, antiasthmatic agent formoterol, antidepressant citalopram, and antitussive agent guaifenesine.
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