Fabrication of TiO2-Carbon Paste Modified Electrochemical Sensor for 4-Aminophenol in Pharmaceutical Samples

In this study the electrochemical behavior of 4-aminophenol at titanium dioxide modified carbon paste electrode was investigated using cyclic voltammetry. The working parameters for both, cyclic- and square wave- voltametric studies have been optimized using 5.0 mM 4-aminophenol (4-APOH) in 0.1 M NaH₂PO₄.2H₂O buffer solution. The modified rather than unmodified carbon paste sensor, in neutral medium, has exhibited strong electro-catalytic activity towards the redox characteristics of 4-aminophenol by showing two-fold peak current enhancement and 174 mV peak potential shift towards negative direction. The red-ox peak current ratio (I _pa/I _pc = 1.6) suggested high accumulation efficiency of 4-APOH at the modified sensor. The redox process is quasi reversible and involves the transference of 2e^-s and 2H⁺s followed by diffusion controlled, non-adsorptive behavior of 4-APOH on the surface of sensor at the interface. Further, the electro-catalytic behavior of the modified sensor has been exploited for quantitative determination of 4-aminophenol in pharmaceutical samples using square wave voltammetry. Under optimal experimental conditions, there was a linear relationship between peak current and concentration in the range 2.5 × 10^-5 to 2.0 × 10^-4 M with a correlation coefficient of 0.998 and limit of detection 1.38 × 10^-8 M. The method was successfully applied for the quantitative determination of 4-aminophenol in pharmaceutical formulations against the commercial drugs viz., PANADOL, and Paracetamol at recovery level of 100 ± 1.7 %.