Rapid sequential determination of the explosives 2,4,6-trinitrotoluene and cyclotrimethylenetrinitramine in forensic samples employing a graphite sheet sensor and cyclic square-wave stripping voltammetry.

The development of a portable analytical procedure is described for rapid sequential detection and quantification of the explosives 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) in forensic samples using a graphite sheet (GS). A single GS platform works as a collector of explosive residues and detector after its assembly into a 3D-printed cell. The detection strategy is based on cyclic square-wave stripping voltammetry. The cathodic scan from + 0.1 to -1.0 V with accumulation at 0.0 V enables the TNT detection (three reduction peaks), and the anodic scan from + 0.2 to + 1.55 V with accumulation at -0.9 V provides the RDX detection (two oxidation processes). Low detection limit values (0.1 µmol L-1 for TNT and 2.4 µmol L-1 for RDX) and wide linear ranges (from 1 to 150 µmol L-1 for TNT and from 20 to 300 µmol L-1 for RDX) were obtained. The sensor did not respond to pentaerythritol tetranitrate (PETN), which was evaluated as a potential interferent, because plastic explosives contain mixtures of TNT, RDX, and PETN. The GS electrode was also evaluated as a collector of TNT and RDX residues spread on different surfaces to simulate forensic scenarios. After swiping over different surfaces (metal, granite, wood, cloths, hands, money bills, and cellphone), the GS electrode was assembled in the 3D-printed cell ready to measure both explosives by the proposed method. In all cases, the presence of TNT and RDX was confirmed, attesting the reliability of the proposed device to act as collector and sensor.

A novel 3D-printed graphite/polylactic acid sensor for the electrochemical determination of 2,4,6-trinitrotoluene residues in environmental waters.

Here, lab-made graphite and polylactic acid (Gpt-PLA) biocomposite materials were used to additively manufacture electrodes via the fused deposition modeling (FDM) technique for subsequent determination of the explosive 2,4,6-trinitrotoluene (TNT, considered a persistent organic pollutant). The surface of the 3D-printed material was characterized by SEM and Raman, which revealed high roughness and the presence of defects in the graphite structure, which enhanced the electrochemical response of TNT. The 3D-printed Gpt-PLA electrode coupled to square wave voltammetry (SWV) showed suitable performance for fastly determining the explosive residues (around 7 s). Two reduction processes at around -0.22 V and -0.36 V were selected for TNT detection, with linear ranges between 1.0 and 10.0 µM. Moreover, detection limits of 0.52 and 0.66 µM were achieved for both reduction steps. The proposed method was applied to determine TNT in different environmental water samples (tap water, river water, and seawater) without a dilution step (direct analysis). Recovery values between 98 and 106% confirmed the accuracy of the analyses. Additionally, adequate selectivity was achieved even in the presence of other explosives commonly used by military agencies, metallic ions commonly found in water, and also some electroactive camouflage species. Such results indicate that the proposed device is promising to quantify TNT residues in environmental samples, a viable on-site analysis strategy.