Thin-layer chromatography — The recovery of separated substances by elution techniques

The purpose of the experiment is to illustrate the elution technique for the recovery of pure substances after their separation by thin-layer chromatography. The experiment can be readily extended to include the quantitative determination of the recovered substances. 

Apparatus. Prepared silica gel plates. Chromatographic tank (see Fig. 8.6). Drummond (or similar) micropipette. 

Chemicals. Indicator solutions ( 0.1 per cent, aq.). Bromophenol blue Congo red phenol red. 

Developing solvent. n-Butanol ethanol-0.2M ammonia (60 20 20 by volume). Chromatographic grade solvents should be used. 

Procedure. Pour the developing solvent into the chromatographic tank to a depth of about 0.5 cm and replace the lid. Take a prepared plate and carefully spot 5 pL of each indicator on the origin line (see Section 8.6, under Sample application) using a micropipette. Allow to dry, slide the plate into the tank and develop the chromatogram by the ascending solvent for about 1 h. Remove the plate, mark the solvent front and dry the plate in an oven at 60 °C for about 15 min. Evaluate the R value for each of the indicators using the equation 

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