Simultaneous voltammetric determination of acetaminophen, aspirin and caffeine using an in situ surfactant-modified multiwalled carbon nanotube paste electrode
Introduction
Combination drugs consisting of acetaminophen (ACOP), aspirin (ASA) and caffeine (CF) are used to treat pain from conditions such as headache (including migraine), muscle aches, menstrual cramps, arthritis, backache, toothaches, colds and sinus infections. However, an overdose of these combination drugs may induce nausea, vomiting, diarrhea, abdominal pain, sweating, seizures, confusion or an irregular heartbeat. Hence, their determination in trace quantities is of great importance. Previously, electrochemical techniques have been implemented for the estimation of ACOP [1], [2], [3], [4], [5], [6], ASA [7], [8], [9] and CF [10], [11], [12], [13], [14] when present individually. Other instrumental techniques employed for the individual analysis of three molecules are: HPLC–MS/MS, GC–MS/MS, spectrofluorimetry for ACOP [15], [16], [17], UV–vis spectrophotometry, solid-phase fluorescence spectroscopy for ASA [18], [19], [20] and GC–MS, micellar electrokinetic capillary chromatography, Quasi-flow injection analysis for CF [21], [22], [23]. However, there are relatively few methods for their simultaneous estimation [24], [25], [26], [27]. Moreover, these methods face the drawbacks of being expensive, laborious and requiring pretreatment of the samples. Surprisingly, no voltammetric procedure exists for the simultaneous determination of ACOP, ASA and CF in a mixture. Therefore, it is desirable to develop simple, sensitive and precise alternate methods employing carbon paste electrodes for the simultaneous determination of all three molecules.
Carbon paste electrodes (CPEs) are very popular due to their wide anodic potential range, low residual current, ease of fabrication, easy surface renewal and low cost. Chemically modified electrodes (CMEs) are used to lower the detection limits compared to plain carbon paste electrodes (PCPE). Various modifiers, such as macrocyclic compounds [28], [29], copper complexes [30], [31], phthalocyanine [32] and nanomaterials [33] have been employed successfully as modifiers for carbon paste electrodes. Carbon nanotubes (CNTs) have triggered a new genre for the development of novel electrode materials due to their amazing structural, mechanical, electrical and physical properties [34], [35], [36], [37], [38]. In addition, surfactants at trace levels have also been employed successfully as modifiers [39], [40], [41], [42], [43].
In view of the desirable characteristics of CNTs and surfactants, it is likely that electrochemical processes may occur in a facile manner on surfactant-CNT modified carbon paste electrodes. Therefore, the present work aims to employ adsorptive stripping differential pulse voltammetry (AdSDPV) for the individual and simultaneous determination of ACOP, ASA and CF at an in situ surfactant-modified multiwalled carbon nanotube paste electrode (ISSM-CNT-PE). The surface characterization of these electrodes is performed using a scanning electron microscope (SEM). The electrochemical characterizations of the obtained electrodes have been carried out through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronocoulometry (CC). Utilizing the developed method, individual and simultaneous determination of the three molecules has been carried out in pharmaceutical formulations, urine and blood serum samples. Additionally, CF was successfully analyzed in beverages, coffee and cola. Moreover, the proposed voltammetric method was validated by UV–vis spectrophotometry for ACOP, potentiometry for CF and titrimetry for ASA.
Section snippets
Chemicals and instrumentation
All chemicals were of A.R. grade and were used as received without any further purification. ACOP, ASA, CF, ascorbic acid, d-glucose, uric acid, NaH2PO4 and Na2HPO4 were purchased from S.D. Fine (India). Urea and 4-aminophenol were procured from Loba Chemie (India). MWCNTs (dimensions: OD = 60–100 nm, ID = 5–10 nm, length = 0.5–50 μm, C 95+%) were obtained from Aldrich (USA). Graphite powder was purchased from S.D. Fine (India). Mineral oil was purchased from Fluka (USA). Sodium lauryl sulfate (SLS),
Effect of pH and supporting electrolyte
Standard solutions of ACOP, ASA and CF (2 × 10−6 M) were used to find the optimum pH of the supporting electrolyte best suited for determination of ACOP, ASA and CF by PCPE. The influence of the pH on the oxidation peaks currents of ACOP, ASA and CF were investigated in the pH range of 2–12 employing Britton–Robinson buffer. It was observed that as the pH of the medium was gradually increased, the potential shifted towards less positive values, suggesting the involvement of protons in the
Conclusion
The results obtained in the paper demonstrate the synergistic effect of TX 100 and an MWCNT modified carbon paste electrode on the first simultaneous voltammetric determination of ACOP, ASA and CF. Additionally, the oxidation peak currents of the three molecules were observed to remarkably increase at the ISSM-CNT-PE surface. Moreover, the proposed method was very sensitive, free of common interferences with the molecules of interest and had sub-micromolar detection limits. This method can be
Acknowledgements
This research was partly funded by the University Grants Commission, New Delhi, India and by the US Army International Technology Center, Tokyo, Japan. We are thankful to Dr. M. Sudersanan for his kind help and suggestions. Thanks are also due to Prof. D.C. Kothari for providing kind help in obtaining SEM images from Icon Analytical.
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