Ultrahigh-resolution capillary electrophoretic separation with indirect ultraviolet detection: isotopic separation of [14N]- and [15N]ammonium.

Separation of isotopically labeled [14N]/[15N] ammonium was performed with capillary electrophoresis. This ultrahigh-resolution separation was based on mobility counterbalance with precise control of the anodic electroosmotic flow. Mixtures of zwitterionic surfactant (Rewoteric AM CAS U) and cationic surfactant (cetyltrimethylammonium bromide) were used as buffer additives to modify the electroosmotic mobility. Indirect ultraviolet detection was used with benzyltributylammonium as the buffer coion. Baseline-resolved peaks of [14N]- and [15N]ammonium were obtained within 11 min. The detection limit was 0.01 mM for both [14N]-and [15N]ammonium. Linear calibration in concentration was observed up to 1.0 mM for [15N]ammonium and 2.0 mM for [14N]ammonium. Calibration of the isotopic ratio, [15N]ammonium concentration to total ([14N] and [15N])ammonium, was valid from 5 to 95%.