Determination of dansyl amino acids and oxalate by hplc with electrogenerated chemiluminescence detection using tris(2,2′-bipyridyl)ruthenium(II) in the mobile phase

A new electrogenerated chemiluminescence detection method is investigated for use in detection in reversed-phase and reversed-phase ion-pair HPLC with Ru(bpy)₃²⁺ in the mobile phase. In this method, different concentrations of Ru(bpy)₃²⁺ are dissolved in the mobile phase and the HPLC column flushed with the mobile phase for 1 h until the column is saturated with Ru(bpy)₃²⁺. The separated analytes along with Ru(bpy)₃²⁺ pass through an optical-electrochemical flow cell which has a dual platinum electrode held at a potential of 1250 mV vs a Ag/ AgC1 reference electrode. On the surface of the electrode, Ru(bpy)₃²⁺ is oxidized to Ru(bpy)₃³⁺ which reacts with the analytes to emit light. The retention times, retention orders, detection limits, and linearity in working curves are compared to those obtained with the conventional postcolumn Ru(bpy)₃²⁺ addition method. The retention times for dansyl ammo acids with Ru(bpy)₃²⁺ in the mobile phase are longer than those obtained with the postcolumn addition approach. This may be caused by π-to-π interactions between the aromatic groups of the dansyl derivatives and the bipyridyl groups of Ru(bpy)₃²⁺ in the Ru(bpy)₃²⁺-saturated reversed-phase column. Similarly, oxalate is separated from urine and blood plasma samples by reversed-phase ion-pair HPLC. Plasma samples are obtained using ultrafiltration to remove proteins from whole blood. Retention times for oxalate with the two detection techniques are identical, and detection limits for these techniques are compared.