The standardisation of thin-layer chromatographic systems for the identification of basic drugs

Three thin-layer chromatographic systems have been selected on the basis of their discriminating power on which to standardise for the identification of basic drugs. They are systems of silica gel sprayed with 0.1 N NaOH, dried and run using one of the following solvents: cyclohexane-toluene-diethylamine (75:15:10), chloroform-methanol (90:10) or acetone. They can be used in combination since their correlation coefficients are low. Four reference compounds should be used, equally spaced across the plate. The inter-laboratory variation of measurement of RF values has been ascertained and the use of a graphical RF correction method reduced the mean deviation of measurement to 0.02. The measurement of RF values was found to be less reproducible in the middle of the chromatogram than in regions of very low or very high RF values.