Modified carbon paste sensor for the potentiometric determination of neostigmine bromide in pharmaceutical formulations, human plasma and urine.

A novel, simple, rapid, selective and sensitive method for the determination of neostigmine (Ns) ion in its bulk powder, different pharmaceutical dosage forms, and biological fluids (plasma and urine) using four modified carbon paste electrodes was developed. Sensor 1 is based on ion-association Ns-TPB, sensor 2 used Ns-PT, sensor 3 comprises a mixture of (Ns-PT+Ns-TPB) and sensor 4 was constructed using (Ns-PT+β-CD). Solvent mediator 2-NPPE exhibited a proper behavior including Nernstian slope ranging from 61.5±0.5 to 64.5±0.5 mV per decade over the pH range of 3.8-10 for the four sensors. Linear responses of Ns within the concentration range 1.0×10(-7)-1.0×10(-2) mol/L were obtained. The response time is very short (≤10s) with a detection limit 6.3×10(-8) M. In flow injection analysis (FIA), sensor 3 shows a Nernstian slope value 75.5±0.5 mV per decade within the concentration range of 1×10(-6)-1×10(-2) mol/L and with a detection limit 7.5×10(-7) mol/L. The utility of mixed or additives of β-CD had a significant influence on increasing the sensitivity of sensors 3 and 4 compared to sensors 1 and 2. The sensors were applied for the determination of neostigmine (Ns) ion in its bulk powder, different pharmaceutical dosage forms, and biological fluids (plasma and urine). The results obtained were satisfactory with excellent percentage recovery comparable with official method for the assay based on non-aqueous titration using perchloric acid as a titrant.