Development of an Electrochemical Method Employing Carbon Screen-Printed Electrodes (C-SPEs) for Detection and Study of MDMA Redox Process
Authors: de Oliveira Marcelo Firmino , Alves Gustavo Murilo , Castro Alex Soares 
Published: May 2020

According to ONU reports, the use of abusive drugs has increased, requiring sensitive techniques for the detection of these substances [1]. This interconnection brings a scenario in which chemical detection of narcotics by conventional, low-cost methods is necessary for drug control. Thus, instrumental analytical techniques appear as indispensable tools for analysis of unknown substances in the forensic field because of their ability to bring low detection limits and selectivity. Thus, the carbon Screen-Printed electrode was elected to develop an electroanalytical method and to study the electrochemical behavior of MDMA for its drug detection potential, low cost, and easy applicability. So, our objective was to develop an electrochemical method with Carbon Screen-Printed electrodes for MDMA detection and study of its redox processes.
Palmsens ® Screen-Printed electrodes were utilized in this work. The behavior de the redox processes of MDMA were carried out with a 1.3×10-3 mol L-1 solution in 0.1 mol L-1 phosphate buffer (PBS) at 2.0, 4.0, 6.0, 8.0, 9.0, and 10.0 pH, since MDMA structure can be protonated at the amino group and turns easier the π orbitals delocalization [2]. The MDMA quantification method development utilized PBS 0.1 M at pH 9.0. The absence of cathodic peaks narrowed the sweeps just as anodic. Thus, Cyclic Voltammetry (CV), Linear Sweep Stripping Voltammetry (LSSV), Differential Pulse Voltammetry (DPSV), and Square Wave Stripping Voltammetry (SWSV) were employed. Adulterants such as caffeine (0.31 mmol L-1), lidocaine (0.25 mmol L-1), acetaminophen (0.66 mmol L-1), AAS (0.28 mmol L-1) and phenacetin (0.56 mmol L-1) were utilized to observe possible interference in the MDMA detection.
The scan rate study indicated that the anodic peak currents are directly proportional the square root of the scan speed in the range from 5 to 100 mV s-1, indicating that the electron transfer reaction of the MDMA on the electrode is diffusion controlled, as predicted by Randles-Sevcik equation. Using carbon SPE, the influence on the change of electrolyte pH through CV was evaluated. Its It was observed that the best currents are obtained at pH 9.0 with supporting electrolyte in 0.1 mol L-1 concentration. For the development of the analytical method, the investigation of the redox processes of MDMA were obtained with LSSV, SWSV and DPSV. The LSSV modality presented the best peak resolution (1.92 ×10-4 AV-1) when compared to SWSV (9.26 × 10-5 AV-1) and DPSV (1.7 × 10-5 AV-1) ). Using LSSV, the equilibrium time parameter was optimized (2.5 to 80 s), such as MDMA preconcentration potential (-1 to 1 V), electrodeposition time (20 to 600 s), and scan speed (5 to 100 mV.s-1) in the potential range from 0.2 to 1.2 V. The best oxidation currents of MDMA were observed at 10 s equilibrium time, -0.5 V preconcentration potential, and electrodeposition time of 20s, using ν = 20 mV.s-1. The merit figures for the developed method were evaluated through analytical curves. PBS solutions at pH 9.0 were prepared with MDMA concentrations ranging from 8.0×10-5 to 1.3×10-3 mol L-1. The analytical curve showed a linear range in this concentration range with detection limit of 7.3×10-5 mol L-1, amperometric sensitivity of 1.43×10-2 A.mol-1.L and linear correlation coefficient of 0.998. Just lidocaine and phenacetin showed electroactivity in this method, but did not demonstrate interference at MDMA response. The results indicated that the analytical method proposed using linear sweep stripping voltammetry showed good analytical performance indicating that the proposed electrode are able to the detection and determination of MDMA in ecstasy samples.

Acknowledgements

FAPESP (process n°2019/04439-3, and 2016/23825-3) and CAPES (Pro-Forenses 25/2014).

References

[1] United Nations Office on Drugs and Crime. (2018). World Drug Report 2018. Book 2

[2] Garrido, E. M. P. J. Electrochemical oxidation of amphetamine-like drugs and application to electroanalysis of ecstasy in human serum. Bioelectrochemistry 79 (2010) 77 - 83.