Miniaturized verapamil solid-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 1x10(-2)-1x10(-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 degrees C), high sensitivity (down to 1 mu g 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.