Flow‐Injection Analysis of Dopamine in Injections with a Periodate‐Selective Electrode

Abstract

Dopamine determination in pharmaceutical preparations based on its oxidation with periodate (IO4−) using a new IO4−‐selective electrode under flow conditions is presented. An electrode with a tubular configuration, no internal reference solution, and a PVC (31.2%) membrane, with metaperiodate bis(triphenylphosphoranylidene)ammonium (1.3%) as ion exchanger and 2‐nitrophenyloctylether (67.5%) as mediator solvent, was used. Optimization procedures were directed at potentials versus dopamine readings instead of potential versus the remaining IO4−. This approach was achieved by selecting a 50‐cm reactor and an overall flow of 7 mL/min, and injecting 70 μL of dopamine standards in a 3.0 × 10−4 M IO4− solution. Under these conditions, a linearity range of 8.0 × 10−3 to 2.7 × 10−1 g/L, with a slope of 310.1 ± 7.4 mV L g−1 and a reproducibility of ±0.4 mV, were recorded (n = 8). Interference from common excipients was negligible. Under these conditions, analysis of dopamine injections (n = 12) presenting 200 mg/injection gave average and standard deviation values of 201.0 and 3.3 mg/injection, respectively. A simple and inexpensive flow‐injection analysis (FIA) manifold, with a good potentiometric detector, enabled the analysis of 200 samples/h without requiring pretreatment procedures. Comparison with the dopamine injection analysis in the United States Pharmacopoeia monograph showed good accuracy, with a relative deviation of −0.2%. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 876–884, 2000