Novel disposable and portable 3D-printed electrochemical apparatus for fast and selective screening of 25E-NBOH in forensic samples

The advent of new psychoactive substances (NPS) has caused enormous difficulty for legal control since they are rapidly commercialized, and their chemical structures are routinely altered. In this aspect, derivatives phenethylamines, such as 25E-NBOH, have received great attention in the forensic scenario. Hence, we propose portable and cost-effective (U$ 5.00) 3D-printed devices for the electrochemical screening of 25E-NBOH for the first time. The cell and all electrodes were printed using acrylonitrile butadiene styrene filament (insulating material) and conductive filament (graphite embedded in a polylactic acid matrix), respectively, both by the fused deposition modeling (FDM) 3D printing technique. The electrochemical apparatus enables micro-volume analysis (50-2000 μL), especially important for low sample volumes. A mechanistic route for the electrochemical oxidation of 25E-NBOH is proposed based on cyclic voltammetric data, which showed two oxidation processes around +0.75 V and +1.00 V and a redox pair between +0.2 and -0.2 V (vs. graphite ink pseudo-reference). A fast and sensitive square-wave voltammetry method was developed, which exhibited a linear working range from 0.85 to 5.1 μmoL-1, detection limit of 0.2 μmol L-1, and good intra-electrode precision (n = 10, RSD <5.3 %). Inter-electrode measurements (n = 3, RSD <9.8 %) also attested that the electrode production process is reproducible. Interference tests in the presence of other drugs frequently found in blotting paper indicated high selectivity of the electrochemical method for screening of 25E-NBOH. Screening analysis of blotting paper confirmed the presence of 25E-NBOH in the seized samples. Moreover, a recovery percentage close to 100 % was found for a spiked saliva sample, suggesting the method's usefulness for quantitative purposes aimed at information on recent drug use.

Electrochemical platform produced by 3D printing for analysis of small volumes using different electrode materials

Fused deposition modeling (FDM) 3D printing is a promising additive manufacturing technique to produce low-cost disposable electrochemical devices. However, the print of devices like well-known screen-printed electrodes (all electrodes on the same device) is difficult using the available technology (few materials available for production of working electrodes). In this paper we present a procedure to produce disposable and robust electrochemical devices by FDM 3D printing that allows reproducible analysis of small volumes (50-2000 μL). The device consists of just two printed parts that allow easy coupling of different conductive materials for using as disposable or non-disposable working electrodes with reproducible geometric area. Printed counter and pseudo-reference electrodes can also be easily fitted into the microcell. Moreover, conventional counter (platinum wire) and mini reference electrodes can also be used. As a proof of concept, paracetamol, cocaine and uric acid were used as model analytes using different materials as working electrodes. Linear calibration curves (r > 0.99) with similar slopes (0.29 ± 0.01 μA μmol L-1; RSD = 3.4%) were obtained by square wave voltammetry (SWV) using a complete printed system and different volumes of standard solutions of paracetamol (50, 100, and 200 μL). For uric acid, a linear range of 10-125 μmol L-1 (r > 0.99), was obtained using differential pulse voltammetry as the electrochemical technique and a disposable laser-induced graphene base as the working electrode. With the coupling of boron-doped diamond working electrode, screening tests were successfully performed in seized cocaine samples with selective detection of cocaine in the presence of its most common adulterants. The production cost per unit of a complete electrochemical system is around US 5.00. In large-scale production, only the working electrode needs to be replaced while the microcell and counter/pseudo reference electrodes do not need to be discarded.

Electrochemical detection of mephedrone using a graphene screen-printed electrode: a new sensitive and selective approach to identify synthetic cathinones in forensic analysis

Mephedrone (MEP) is an illicit stimulant drug that belongs to the synthetic cathinone (SC) class, which has been widely used for recreational purposes and reported in forensic analysis. The preliminary identification of MEP and other SCs in seized samples is of great interest for forensic investigation and a fast and simple screening test for these drugs would be useful for on-site and in-house analyses. In this study, we present the electrochemical detection of MEP in forensic samples using, for the first time, independent redox processes of SCs on a graphene screen-printed electrode (SPE-GP). The proposed method for MEP detection on the SPE-GP was optimized in Britton-Robinson buffer solution (0.1 mol L^-1) at pH 10.0 with adsorptive stripping differential pulse voltammetry (AdSDPV). The use of the SPE-GP with AdSDPV provides a wide linear range for MEP determination (2.6 to 112 μmol L^-1) with a low limit of detection (LOD) (0.3 μmol L^-1). The real surface area available for adsorption on the SPE-GP was estimated to be between 3.80 and 5.70 cm², which provided high sensitivity for the proposed method. Furthermore, good stability of MEP electrochemical responses on the SPE-GP was obtained using the same or different electrodes (N = 3), with relative standard deviation (RSD) < 5.0% for both redox processes. Interference studies for a common adulterant (caffeine) and twelve other illicit drugs (phenethylamines, amphetamines, and other SCs) were performed with a highly selective response for MEP detection. Therefore, the SPE-GP with AdSDPV is demonstrated to be a selective and sensitive screening method to detect MEP and other SCs in forensic analysis, providing a fast and simple preliminary identification of these drugs in seized samples.

Development of a simple and rapid screening method for the detection of 1-(3-chlorophenyl)piperazine in forensic samples

1-(3-chlorophenyl) piperazine (mCPP) is a synthetic drug with hallucinogenic effects that has often been found in seized samples. In this context, easy to use point-of-care tests can be of great value in preliminary forensic analysis. Herein, we proposed a simple, fast, and portable electrochemical method for the detection of mCPP in seized samples. The method is based on the use of disposable screen-printed carbon electrodes (SPCE) and rapid screening procedures by square-wave voltammetry using minimal sample sizes (100 μL). mCPP showed an irreversible electrochemical oxidation process at +0.65 V on SPCE (vs Ag) using 0.04 mol L^-1 Britton Robinson (BR) buffer solution (pH 7) as the supporting electrolyte. The proposed method exhibited a linear correlation (r = 0.998) between peak current and mCPP concentration in the range of 1-30 μmol L^-1 (LOD = 0.1 μmol L^-1). Interference studies were performed for adulterants and other classes of drugs of abuse, which can also be found in seized samples containing mCPP, such as caffeine, amphetamine, methamphetamine, 1-benzylpiperazine, 3,4-methylenedioxymethamphetamine, methylone, mephedrone, ethylone and 3, 4-methylenedioxypyrovalerone. The developed method presents great potential as a rapid and simple screening tool to detect mCPP in forensic samples.

Dehydration of D-fructose to 5-hydroxymethyl-2-furfural in DMSO using a hydrophilic sulfonated silica catalyst in a process promoted by microwave irradiation

SiO₂-SO₃H, with a surface area of 115 m²/g, pore volumes of 0.38 cm³g^-1 and 1.32 mmol H⁺/g, was used as a 10% w/w catalyst for the preparation of 5-hydroxymethyl-2-furfural (HMF) from fructose. A conversion of 100% was achieved in a microwave reactor during 10 min at 150 °C in DMSO, with 100% selectivity for HMF, at a molar ratio of fructose: DMSO equal to 1:56. The catalyst could be re-used three times.