A Modified Technique in Chromatography

Abstract

THE methods usually adopted for the chromatographic separation of inorganic radicals on filter paper or an adsorbent column lead to the formation of coloured zones with diffusion fronts which are distorted and irregular. We have now developed a method for obtaining sharp, straight and evenly coloured bands for each one of the radicals separated. Strips of Whatman filter paper (No. 1), are dipped in a hot agar sol (2–4 per cent) containing reagents which react with the radicals to be tested. The strips are then removed from the agar sol and the excess sol drained off, leaving a thin layer of the sol on the surface of the paper, which solidifies to a gel on cooling. The paper strip thus prepared is then immersed to a height of 5 mm. in an aqueous solution containing the radicals to be tested (the concentration of the solution being 0.1 N with respect to each ion). As the electrolytes diffuse into the agar-gel impregnated filter paper containing the appropriate reagents, sharp, straight zones of the characteristic coloured precipitates are produced. When the layer of the gel coating on the paper is thick, these coloured bands show a fine structure due to Liesegang ring formation. In a run of four hours, bands of sufficient width for accurate measurement with a travelling microscope are produced in accordance with the solubility-product principle discussed previously¹