Procedures for selected chromatographic separations

Group I. Ag, Pb, and Hg The metals are present as nitrates in dilute nitric acid. The solution is spotted upon paper and allowed to dry in air for one hour. The solvent consists of n-butyl alcohol, mixed with 5 per cent (v/v) glacial acetic acid, followed by water to turbidity. The separation (elution) is allowed to proceed for 12-16 hours in an atmosphere saturated with the solvent. The strip 

The paper chromatogram may also be developed by exposure to hydrogen sulphide gas, but the results are not as satisfactory as with dithizone. 

Group IIA. Hg, Pb, Bi, Cu, and Cd The metals are present as chlorides in dilute hydrochloric acid. The solvent used is n-butyl alcohol saturated with 3m hydrochloric acid. To obtain a good separation of copper and lead, the strip should be at least 45 cm long. The solvent is allowed to flow for 15-18 hours in an atmosphere saturated with respect to both organic solvent and aqueous phases. After evaporation of the solvent, the strip is sprayed with a solution of dithizone in chloroform (0 05 per cent w/v). Lead gives only a weak colour with dithizone and is best detected by spraying the top portion of the strip with an aqueous solution of rhodizonic acid. 

A chromatogram (drawn from an actual photograph) is shown in Fig. VI. 5a. 

Group IIB. As, Sb, and Sn The separation of a mixture of the three elements is a difficult operation. The metals are present as their lower chlorides in dilute (2-4m) hydrochloric acid. The solution is spotted on paper and allowed to dry in air for 15 minutes. The solvent consists of 7-5 ml acetylacetone (b.p. 137°-141°) saturated with water and treated with 0 05 ml concentrated hydrochloric acid and 2-5 ml acetone (sufficient of the last-named to give a clear solution). The separation is allowed to proceed for 1 hour in an atmosphere saturated with respect to a saturated solution of acetylacetone in water the solvent movement is about 15 cm. The complexes formed are very stable, particularly that with tin (Rf = 1). The strip is removed from the extraction vessel, the solvent is allowed to evaporate for several minutes, and the strip is sprayed (before it is completely dry) with a chloroform solution of dithizone (0-005 per cent w/v), and then allowed to dry thoroughly. The tin is found in the solvent front. 

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