Miniaturized Verapamil Soild-State Potentiometric Sensors Based on Native Ionic Polymers

 Novel miniaturized carboxylated poly(vinyl chloride) and poly fluoro sulfonate (Nafion) matrix membrane sensors in an all-solid state graphite support were developed, electrochemically evaluated and used for the assay of verapamil drug. These sensors incorporate the native polymers without plasticizer and/or drug-ion pair complex. Upon soaking these sensors in verapamil test solution, electroactive self regenerated membranes are formed and a near-Nernstian potentiometric response is induced for verapamil over the concentration range 1×10⁻²–1×10⁻⁵ M with a cationic slope of 56–57 mV decade⁻¹ of concentration. Inherent advantages of these sensors include fast response (<10 s), long life time (>6 months), good thermal stability (up to 60 °C), high sensitivity (down to 1 μg ml⁻¹), extended working pH range (2–8) and reasonable selectivity. Verapamil could be determined in various dosage forms with an average recovery of 98.8% (st.dev. 0.8%) of the nominal concentration without any significant interferences from various excipients and diluents commonly used in drug formulations. Received August 17, 1998. Revision February 9, 1999.