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A new and sensitive electroanalytical method for simultaneous determination of selected drugs, 4-aminophenazone (4-AP) and caffeine (CAF) has been developed and validated. Cyclic voltammetry (CV) was used to study the electrochemical behavior of the drugs, while differential pulse voltammetry (DPV) was used to determine 4-AP and CAF simultaneously. A pre-treated graphite pencil electrode (PTGPE) was used as the working electrode, a Ag/AgCl (3.0 M KCl) electrode served as the reference electrode, and a platinum wire as the auxiliary electrode. Determination of drugs was performed in phosphate buffer solution (PBS) of pH ¼ 3.0. The separation of the oxidation peak potentials for 4-AP-CAF was found to be 0.930 V. This difference was large enough to determine 4-AP and CAF individually and simultaneously. The dependence of the current on pH, concentration and scan rate was investigated to optimize the experimental conditions for simultaneous determination. The calibration plots for both the drugs were linear in certain concentration ranges. The linearity range for 4-AP was 1 mM to 11 mM and for CAF 1 mM to 9 mM, the concentration of each drug was varied by keeping the other constant, and achieved lower detection limit of 7.96 Â 10 À8 M for 4-AP and 9.81 Â 10 À9 M for CAF. The developed method was found to be precise, selective and rapid for the simultaneous determination of 4-AP and CAF. The proposed method has been applied for the determination of 4-AP and CAF in real samples.Scheme 1 Chemical structure of 4-AP and CAF.

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An electrochemical sensor for sensitive detection of paracetamol (PCM) was developed by constructing the glassy carbon electrode (GCE) modified with multiwalled carbon nanotubecetyltrimethyl ammonium bromide (MWCNT-CTAB). Modification improves the redox kinetics of PCM with increased current intensity. A similar modification at CTAB modified GCE did not result in an impressive charge transfer. Detection limit of PCM was determined from differential pulse voltammetric (DPV) study and found to be 4.82×10 −9 M with a linear dynamic range of 4.0×10 −7 M to 4.0×10 −6 M. The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of interferents and response is fast, stable, reliable, resistant to biofouling and can be applied for the real sample analysis in medical, pharmaceutical and biotechnological sectors.Kinetic parameters were determined using electrochemical approaches. The practical analytical application of this electrode was demonstrated by measurement of PCM content in PYREMOL 650 tablet and real sample analysis.