A Novel Method for Quantitative Thin Layer Chromatography The well-known paper chromatography method of quantitation by weighing cut out spot areas has been applied to thin layer ehromatograms by a simple technique. Separation of phenol and 4,4'-diphenylolpropane was achieved by thin layer chromatography on s 0.2-mm layer of Silica Gel H. (Merck reagent) using two elutions with benzene-methanol-ethyl acetate (90:2:8)' for development. The samples were placed on the plate in lpl aliquots by means of a syringe. Different concentrations for standards were obtained by overlaying 1-pl amounts thus ensuring constant initial spot size. After development the chromatogram was visualized by spraying with a 0.2% ethanol solution of 2,6-dihromoquinone chlorimide followed by exposure to ammonia fumes.2 The boundaries of the spots were marked with a pointed instrument. The chromatogram was then photocopied, using a standard office photostat machine. The ehromatograms could be safely lowered, face down, onto the copy plate without any disruption to the surface. Spot images on the photocopy were cut out and weighed. A calibration was prepared by using a series of concentrations and correlating, by least squares, the weight of the spot and the concentration. Statistical Correlation of Spot Weight
C
Phenol W = 0.40C + 1.87 ID = 0.83 W %( w-w,,~,I
Verrur Concentration
4.4'-~iphenylolpropane W = 0.64C + 0.99 ID = 0.93 C W %( w- Wcalcl
W = Weight of spot (mg) C = concentration of component (mole %I I D = Index o f determination.
The table shows some results obtained for phenol and 4,4'-diphenylolpropane. The % error values are quite reasonable for this type of technique. Advantages of the method are that it is inexpensive simple and quantitative results can be achieved without destroying the chromatogram. I
Braun, D., and Lee, D. W.,Kunstoffe,62,574 (1972). Bobbitt J. M., "Thin Layer Chromatography," Reinhold, New York, 1963, p. 92.
Monsanta Australian Limited, P.O. Box 62, West Footseray, Vie. 3012, Australia.
738 / Journal of Chemical Education
D. E. Baum R. A. Shanks
