Although spectral reflectance has found application in the solution of a wide range of problems, surprisingly little use has been made of this technique in analytical work. Some of the potentialities of the method, particularly in biochemical analysis, have been pointed out by Naughton et al. (1). More recently the analysis of amino acids by means of thinlayer chromatography has provided another example of a situation in which spectral reflectance can be used to obtain analytical data simply and with a minimum of preparative and extractive operations.
Several direct photometric techniques have been devised for the in situ estimation of amino acids separated by paper chromatography (2-7). Although some of these procedures could be adapted for use in such investigations as the study of factors affecting recoveries from paper chromatograms and the stabilization of colors developed on paper, they are not applicable to chromatoplates. The possibility of using reflectance measurements to accomplish this in separations involving thin plates was suggested by a study of the application of spectral reflectance to thin-layer chromatography (8). As a result of this study, it was decided to employ the technique to investigate some of the factors affecting the color stability of the ninhydrin complex of leucine adsorbed on silica gel.