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A Rubber Ruler for Determination of R, Values for Thin Layer Chromatography Rf values tix thin layer chromatography are often calculated by dividing the distance the substance travels hy the distance between the , , , , origin and the solvent front. Tw,measurements and a division are required. Ri values can he determined in one easy operation, however, hy using a ruhher ruler. A ruhher ruler can be made hy simply adding the appropriate scale tu a length of uniform ruhber hand or tuhing. A scale with a range fnrm 0.0 to 1.0 in divisions of 0.02 will permit Hi values accurate t o two sig, nilicant figures. T o determine Rf values, stretch the ruler until the 0.0 end of the scale is positioned a t the origin and the 1.0 end a t the solvent 1 . . front. Then read the Ri values of every spot directly from the scale. Select a pieceof ruhher about 15-20 cm long. Make two small dots with a hall paint pen ahout 5 em apart near the center section. Stretch the ruhher until the dots are about 10 cm apart and then clamp it to a meter stick with two screw clamps. Clamp near the ends of the ruhher t o avoid distortion. U'ith a s e c m d metric ruler and a hall paint pen mark o f f a scale (approximately between the dots) 10 cm Imp, with divisims every 2 mm. Starting at m e end, lahel each centimeter mark 0.0,O.l.. . . u p tu 1.0. Unclamp theruhher and thescale will shl.ink toahout 5 cm.The unstretched scale should he shorter than the distance between the origin and the solvent front. A 5-cm ruler will he suitable for thin layer chromatography plates coated on micnrswpe slides. A ruler for larger plates would require less stretching hefore the scale is drawn (use -8 o r Y em hetween dots instead 01'5 cm and then stretch to 10 cm.). Ball point pen ink marks well on ruhher and will he relatively permanent if a l l w e d 10 set for a few days hefore handling. Gene A. Hiegel California S t a t e University, Fullerton Fullcrton, 92634
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Volume 55,Number 1, January 1978 I 59
