Reversed phase extraction chromatography using solutions of nitric acid as eluants

Approximately 40 ions have been chromatographed on thin layers of silica gel impregnated with Alamine 336-S, Alamine 336-S oxide, tri-n-octylarsine oxide, tri-n-octylphosphine oxide or tri-n-butyl phosphate, and on non-impregnated silica gel. Solutions of 0.2–15 N HNO₃ are used as eluants. R_F spectra and a number of separations are reported. The ions are classified into four groups according to their chromatographic behaviour, which is explained on the basis of anion exchange, solvation, hydrolysis and interaction with the support.Data on the extraction of HNO₃ and the co-extraction of water are reported. The behaviour of Alamine oxide and tri-n-octylarsine oxide parallels that of high-molecular-weight amines: extraction proceeds through anion exchange. Nitric acid taken up in excess of the stoichiometric amount is mainly present in the organic phase as part of the ion [O₂NO…HONO₂]⁻. On the other hand, with tri-n-octyl-phosphine oxide (TOPO) and tri-n-butyl phosphate (TBP), extraction proceeds through solvation; TOPO·HNO₃, TOPO·2HNO₃ and TBP·HNO₃ are the species present in the organic extracts.