Simultaneous determination of caffeine and theophylline using square wave voltammetry at poly(l-aspartic acid)/functionalized multi-walled carbon nanotubes composite modified electrode

A simple and reproducible poly(l-aspartic acid)/functionalized multi-walled carbon nanotubes composite modified glassy carbon electrode, P(LAsp)/f-MWCNTs/GCE, was constructed for simultaneous determination of caffeine and theophylline using square wave voltammetry. The electrode preserves and combines the properties of the individual modifiers synergistically. The electrochemical response of P(LAsp)/f-MWCNTs/GCE was characterized by cyclic voltammetry. A significant enhancement in the peak current response of CF and TP were observed accompanied with a negative shift in peak potential at the composite modified electrode compared to the bare electrode. The prepared P(LAsp)/f-MWCNTs/GCE exhibited excellent SWV response towards the simultaneous detection of CF and TP in the range of 1-150 and 0.1-50 μM with limit of detection of 0.28 and 0.02 μM (S/N = 3), respectively. Real sample analysis has been successfully carried out in green tea, blood serum and pharmaceutical formulation of Panadol extra samples, which revealed good recovery results, 92.0-106%. The proposed sensor also displayed good selectivity, repeatability and reproducibility with appreciable long-term stability, indicating the feasibility and reliability.