Continuous I’rei’ara’ixve Thin-layer Chromatography

Cllromatcqgq~ily has its main application in solving analytical problems, but since it can lx-oducc essentially l)ure conq~ounds, prcl~arativc methods are of interest for synthetic \vork, for those identification techniques which riced nig amounts and for isolation of minor constituents in mistures. " Scaling-up " of the separation can be effect4 by cnlargemcnt of dimensions, by reiteration of a given cycle, if possible by automatic methods, and by continuous or semi-continuous procedures. Scmi-continuous methods are IT~ildd' as consisting of a series of pilysicaily sqx~ratccl noii-continuous systems folio\ving each other ilt constant time intervals. For g:Ls-iiclui(l ci~rom;~togrnl~lly tile first tivo methods, ,i.c. with large coiumnsl-4 and Lvith a Wp~iltd CyciCG-7 arc lvell-kno\vn. Rcccntly, some continuous methods 1lilVC been dcscril~cd8-10, based on the counter-current principle, but their application stems to ix limited. A semi-continuous inetliod (" simultaneous multi-column anaiy-sis ") has also been rcIxxtedll. In l)alxx chrom~ltogrnI~l~y both large-scalc12-lB and contiiiuous17~1H procedures are npplicd. For column cliromatograpiiy large-scale teciiniclucs10~2'~ an d a semi-continuous method have been described2l. Eicgant methods for iLlr~~-SCiliC22 and continuous*3*24 eicctrol~iiorcsis arcs well-known. l~inaiiy, large-scale prcparativc tilin-layer ci~r~~~l~~~t~~gri~l~ily 1x1s rcccntiy been dcvciolxx12G. Tily has been widely used for an alyticai purposes, but no continuous Txcparative motllocls ilavc so far been described. Both principles, cyiin-drical and circular, are at prcscnt being studied but in this paper only the aualoguc of a cylindrical system will be cliscussed.