Large-Scale, Preparative Paper Chromatography

Most of the techniques that have been described for large-scale, preparative paper c hromatograp hy depe nd on an i.ncrease in bulk through the use of many closely pressed layers of a thin paper [IJ.' So me of these methods require the tedious loading of each s hee t , and others tend to suffer from a lack of uniformity in the movement of compounds thro ughout the bulk. Th e latter disadvantage has been overcome in one commercial apparatus by e mpirically regulating the press ure [2 J. In 1957, Brownell and co-workers [3J described a large-scale, heavy-paper technique for preparative c hromatography in which, after a preliminary treatment, the paper is used in essentially the cus tomary manner. The authors stated that the dense paper (Whatman seed~ test paper, 1.5 mm thic k) is capable of separating 0.5 to 3.0 g of material per large sheet (18 X 22 in), depending on the spread in Rf values.2 They also described a method for nond estructively locating the separated bands by staining a " print" obtained by pressing a sheet of thin paper against the wet chromatogram. However, despite the unusually high capacity of th e heavy paper, and the inherent advantages of paper c hromatography over column chromatography, the techniques described by Brownell et al. have not been widely adopted, presumably because of several diffi c ulties encountered in using the heavy paper. Thus, (a) the edge of the paper must be provided with a machine·s titc hed stirrup or loop (for supporting the