Retention behavior of nitrite on a reversed-phase column with an acidic aqueous eluent containing alcohol as a modifier

Abstract

The retention behavior of nitrite on two octadecyl modified reversed-phase columns, a poly(vinylalcohol) gel-based Asahipak ODP-50 and a silica gel-based LiChrosorb C-18 columns, was studied. Nitrite was retained only on the ODP column when dilute sulfuric acid was used as an eluent. With the addition of alcohol as an organic modifier, nitrite was retained on both columns. The capacity ratio and the peak shape of nitrite on the ODP column were controlled by the concentrations of sulfuric acid and alcohol in the eluent. The capacity ratio, k′, of nitrite can be described as the sum of the contribution of the ion-exchange process between nitrite anion and a fixed quaternary ammonium group and those of the esterification processes between nitric acid and hydroxyl groups. The latter process consists of the distribution of the hydrophobic nitrite ester yielded by the reaction with alcohol in the mobile phase and in the solvated layer on the ligand. The reaction of nitrous acid with a hydroxyl group remaining on the gel surface also participates in the retention of nitrite. The retention of nitrite on the LiChrosorb C-18 column was controlled by the esterification process with alcohol in the eluent.