Application of capillary electrophoresis in anion binding studies: complexation and separation of nitrate and nitrite by an azacryptand

Capillary electrophoresis (CE) was employed to study the complexation of an azacryptand with nitrate and nitrite in aqueous solution. CE separation of a mixture of nitrate and nitrite with 10 mM acetate buffer (pH 3.3) showed two peaks at the retention times of 2.8 and 3.1 min for nitrate and nitrite, respectively. However, when the ligand (2 mM) was added to the running buffer, the peaks emerged in the reverse order and at shorter retention times of 2.7 and 2.5 min for nitrate and nitrite, respectively. The longer retention time for nitrate compared with nitrite indicates a stronger complex formation between the ligand and nitrate, which reduces the migration speed of nitrate as compared with the less strongly bound nitrite. The H-1 NMR titrations of L with these two anions at the pH 3.3 gave the binding constants (log K), 3.75 and 4.23, for nitrite and nitrate, respectively which were consistent with the results obtained from the CE method. Copyright (C) 2010 John Wiley & Sons, Ltd.