Simultaneous determination of methadone and morphine at a modified electrode with 3D β-MnO2 nanoflowers: application for pharmaceutical sample analysis

Abstract

The present research synthesized manganese dioxide nano-flowers (β-MnO₂-NF) via a simplified technique for electro-catalytic utilization. Moreover, morphological characteristics and X-ray analyses showed Mn in the oxide form with β-type crystallographic structure. In addition, the research proposed a new efficient electro-chemical sensor to detect methadone at the modified glassy carbon electrode (β-MnO₂-NF/GCE). It has been found that oxidizing methadone is irreversible and shows a diffusion controlled procedure at the β-MnO₂-NF/GCE. Moreover, β-MnO₂-NF/GCE was considerably enhanced in the anodic peak current of methadone related to the separation of morphine and methadone overlapping voltammetric responses with probable difference of 510 mV. In addition, a linear increase has been observed between the catalytic peak currents gained by the differential pulse voltammetry (DPV) of morphine and methadone and their concentrations in the range between 0.1-200.0 μM and 0.1-250.0 μM, respectively. Furthermore, the limits of detection (LOD) for methadone and morphine were found to be 5.6 nM and 8.3 nM, respectively. It has been found that our electrode could have a successful application for detecting methadone and morphine in the drug dose form, urine, and saliva samples. Thus, this condition demonstrated that β-MnO₂-NF/GCE displays good analytical performances for the detection of methadone.

Fig. 1. XRD pattern of β-MnO₂ nano-flowers.

Fig. 2. (A) FESEM image of β-MnO₂ nano-flowers, (B) FESEM images of a single β-MnO₂ nano-flowers.

Fig. 3. EDX spectra and elemental mapping of the β-MnO₂ nano-flowers.

Fig. 4. (A) CV acquired at a potential scan rate 50 mV s⁻¹ for a 0.5 mM [Fe(CN)₆]^3−/4− in aqueous 0.1 M KCl at the (a) bare GCE and (b) β-MnO₂-NF/GCE. (B) CVs of β-MnO₂-NF/GCE in the presence of 0.5 mM [Fe(CN)₆]³⁻ solution in aqueous 0.1 M KCl at various scan rates (from inner to outer curve): 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, and 900 mV s⁻¹. (C) The plot of peak currents vs. ν^1/2.

Fig. 5. EIS diagrams for 0.5 mM [Fe(CN)₆]^3−/4− solution at (a) unmodified GCE and (b) β-MnO₂-NF/GCE in aqueous 0.1 M KCl. Frequency range from 100 kHz to 0.1 Hz.

Fig. 6. CVs of (a) β-MnO₂-NF/GCE and (b) unmodified GCE in the presence of methadone (100.0 μM) at a pH 7.0, respectively. In all the cases, the scan rate was 50 mV s⁻¹.

Fig. 7. (A) Effect of pH on the peak current for the oxidation of methadone (50.0 μM); pH = 3–9. In all the cases, the scan rate was 50 mV s⁻¹. (B) The plot of peak potential vs. pH.

Scheme 1. The probable oxidation mechanism of methadone.

Fig. 8. (A) CVs of β-MnO₂-NF/GCE in pH 7.0 in the presence of methadone (350.0 μM) at various scan rates (from inner to outer curve): 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, and 1000 mV s⁻¹. (B) The plots of peak currents vs. ν^1/2.

Fig. 9. (A) Chronoamperograms obtained at β-MnO₂-NF/GCE in 0.1 M PBS (pH 7.0) for different concentrations of methadone (from inner to outer curve): 0.02, 0.04, 0.08, and 0.12 mM. (B) Plots of I vs. t^−1/2 obtained from chronoamperograms 1–4. (C) Plot of the slope of the straight lines against methadone concentration.

Fig. 10. (A) Chronoamperometric responses on β-MnO₂-NF/GCE in the absence or presence of 0.01 mM methadone, in 0.1 M (pH 7.0); (B) Plot of I_C/I_Lvs. t^1/2.

Fig. 11. (B) DPVs of β-MnO₂-NF/GCE in 0.1 M (pH 7.0) containing different concentrations of morphine and methadone (from inner to outer curve): 0.1 + 1.0, 0.5 + 10.0, 1.0 + 20.0, 10.0 + 30.0, 20.0 + 40.0, 30.0 + 50.0, 40.0 + 60.0, 50.0 + 70.0, 60.0 + 80.0, 70.0 + 90.0, 80.0 + 100.0, 90.0 + 125.0, 100.0 + 150.0, 125.0 + 175.0, 150.0 + 200.0, 175.0 + 225.0, and 200.0 + 250.0 μM. (A) and (C) Plots of the electrocatalytic peak current as a function of morphine and methadone concentration in the range of 0.1 to 200.0 μM and 0.1 to 250.0, respectively.

Fig. 12. (A) DPVs of β-MnO₂-NF/GCE in 0.1 M (pH 7.0) containing 20.0 μM of methadone and different concentrations of morphine (from inner to outer curve): 50.0, 60.0, 70.0, 80.0, 90.0, 100.0, 115.0, 130.0, 145.0, and 160.0 μM. (B) Analytical curve from morphine, (C) 150.0 μM of AM, and different concentrations of methadone (from inner to outer curve): 70.0, 80.0, 90.0, 100.0, 125.0, 150.0, 175.0, 200.0, 225.0, and 250.0 μM, (D) analytical curve from methadone.

Fig. 13. (A) The columns are the current change of β-MnO₂-NF/GCE in 0.1 M PBS (pH = 7.0) solution containing (a) 100.0 μM methadone, (b) a + 1.0 mM ascorbic acid, (c) a + 4.5 1.0 mM uric acid, (d) a + 4.5 1.0 mM tyrosine, (e) a + 1.0 mM naltrexone, (f) a + 1.0 mM Heroine, (g) a + 1.0 mM papaverine, (h) a + 1.0 mM buprenorphine, and (i) a + 1.0 mM thebaine. (B) The columns are the current change of β-MnO₂-NF/GCE in 0.1 M PBS (pH = 7.0) solution containing (a) 100.0 μM Morphine, (b) a + 1.0 mM ascorbic acid, (c) a + 4.5 1.0 mM uric acid, (d) a + 4.5 1.0 mM tyrosine, (e) a + 1.0 mM naltrexone, (f) a + 1.0 mM heroine, (g) a + 1.0 mM papaverine, (h) a + 1.0 mM buprenorphine, and (i) a + 1.0 mM thebaine.

Fig. 14. (a) CVs of β-MnO₂-NF/GCE in 0.1 M PBS (pH 7.0) containing 100.0 μM methadone and (b) after 30 days.