AUGUST, 1&
PROPORTIONAL DIVIDER FOR RAPID DETERMINATION OF CHROMATOGRAPHIC Rf VALUES DAVID F. HOUSTON Western Utilization Research Branch, United States Department of Agriculture, Albany, California
A SIMPLE device is described for rapid determinatiou of chromatographic Rf values. Its combined ease of construction, simplicity of use, and ruggedness offer advantages over related devices previously described.' These qualities also make it desirable for student use in experiments on chromatographic procedures. The device consists of a single piece of l/la-inch transparent, colorless plastic material, such as methyl methacrylate polymer, in the form of a right triangle as illustrated. Twenty lines are inscribed on this from one acute angle to points on the opposite edge mhich are spaced apart by five per cent of the length of the edge. Indicia are inscribed along thissame edge. The edges forming the right angle may be of the same or different lengths; however, the scale side must be longer than the distance from the original spot. on the chromatogram to the final solvent front. The inscribed lines show clearly and may be used as formed, or they may be filled with a pigmented material. In use, the device is placed over the strip or two-way chrom?,togram with its base (nonscale side) on a line through the original spot parallel to the bottom edge of the paper. The triangle is then moved sideways until its hypotenuse intersects the solvent front a t a poiut directly above the spot being measured. (The right triangle may also be used to erect a perpendicular a t this point.) The Rf value of the selected point on the chromatogrammed spot to be determined is read to the nearest 0.05 and estimated to 0.01. The Rf velue PHILLIPS, D . M. P., Nature, 162, 29 (1948); ROCKLAND, L. Science, 111, 332 (1950); NETTLETON, R. B., A N D M. 8. DUNN, M., AND R. B. MEPPERD, And. Chem., 24, 1687 (1952); GLAZKO, A. .I. .AND , W. A. DII.L, ibid., 25;1782(1953).
of the spot in a second solvent is similarly determined. The device may also be readily used t o determine Rx, where distance of travel of a known substance is used as a reference instead of distance t o the solvent front. Here a line to replace the solvent front is drawn through the selected point on the reference spot parallel to the base line. If the unknown has traveled further thau the reference material, the line is drawn through the chosen point on the unknown spot. The ratio of reference spot t o unknown is determined, and the reciprocal is taken.
