B. Carry out the method for thin-layer chromatography, Appendix III A, using silica gel G as the coating substance and a mixture of 1 volume of a 15% w/v solution of ammonium acetate previously adjusted to p 7.0, 15 volumes of ethanol (96%) and 85 volumes of chloroform as the mobile phase. Apply separately to the plate 10 ul of each of the following solutions. For solution (1) dissolve a quantity of the residue in acetone to produce a solution containing the equivalent of 0.1% w/v of erythromycin. Solution (2) contains 0.1% w/v of erythromycin ethylsuccinate BPCRS in acetone. Solution (3) contains 0.1% w/v of erythromycin ethylsuccinate BPCRS and 0.1% w/v of erythromycin estolate BPCRS in acetone. After removal of the plate, allow it to dru in air sprav with anisaldehyde solution, heat at 1109 for