Circumstances of Multi-spot Paper Chromatograms of Sodium Orthophosphates: in situ Identification of the Species

Abstract

THE formation of more than one zone containing phosphate when the sodium orthophosphates are chromatographed on paper suggests that these spots contain different molecular species originating in proton transfer equilibria of the kind: where B⁻ⁿ is a base^1,2. The speed of proton transfers, for example, the half-life for the reaction of hydronium and hydroxyl ions is 10⁻⁸ sec³, argues against this as such equilibria yield multiple spots only if the transition time is comparable with the time required for the formation of the chromatogram⁴. It is natural to question next if the zones are actually of different species since discontinuities in either the immobile or mobile phases can also produce the result⁴. Chromatograms of orthophosphoric acid and of the primary, secondary, and tertiary sodium salts were formed on 55 cm × 2.8 cm strips of Whatman No. 1 filter paper, acid washed, which had also been washed in 2 M acetic acid followed by three successive rinsings in distilled water⁵. The chromatograms were formed either with pyridine/ethyl acetate/water (the faster solvent) or butanol/water. Fig. 1 is a photograph of 10 µl. of 0.01 M trisodium phosphate (No. 321) and 10 µl. of 0.01 M sodium dihydrogen phosphate (No. 322) formed simultaneously with BuOH/15 per cent H₂O. The origin was the vertical pencil line adjacent to the numbers. When revealed, the colour process was that employing ammonium molybdate and benzidine hydrochloride⁶. In certain select cases, the multiple spots were irradiated in the University's Triga reactor^7,8. Both sodium and phosphorus undergo (n,γ)·reactions to form radioactive isotopes which decay as follows^9,10: