Maiara O. Salles

Explosive colorimetric discrimination using a smartphone, paper device and chemometrical approach

In this report we introduce a novel approach for an inexpensive and disposable colorimetric paper sensor array for the detection and discrimination of five explosives – triacetone triperoxide (TATP), hexamethylene triperoxide diamine (HMTD), 4-amino-2-nitrophenol (4A2NP), nitrobenzene (NB), and picric acid (PA). The colorimetric sensor comprised a disposable paper array fabricated using a wax printer and three reagents (KI, creatinine, and aniline) that produced a unique color pattern for each explosive based on chemical interactions between the explosive species and the chemical reagents. The analytes were discriminated from one another as per the color change profiles, which were readily distinguishable after 15 min, using hierarchical clustering analysis (HCA) and principal component analysis (PCA); there were no misclassifications in any of the trials conducted. The colorimetric pattern values were extracted using a smartphone, custom-made software and a closed chamber to circumvent the illumination problems commonly found in other paper approach devices. A semi-quantitative analysis was performed and it was possible to use as low as 0.2 μg of explosives.

Flow injection analysis of picric acid explosive using a copper electrode as electrochemical detector.

A simple and fast electrochemical method for quantitative analysis of picric acid explosive (nitro-explosive) based on its electrochemical reduction at copper surfaces is reported. To achieve a higher sample throughput, the electrochemical sensor was adapted in a flow injection system. Under optimal experimental conditions, the peak current response increases linearly with picric acid concentration over the range of 20-300 μmol L(-1). The repeatability of the electrode response in the flow injection analysis (FIA) configuration was evaluated as 3% (n=10), and the detection limit of the method was estimated to be 6.0 μmol L(-1) (S/N=3). The sample throughput under optimised conditions was estimated to be 550 samples h(-1). Peroxide explosives like triacetone triperoxide (TATP) and hexamethylene triperoxide diamine (HMTD) were tested as potential interfering substances for the proposed method, and no significant interference by these explosives was noticed. The proposed method has interesting analytical parameters, environmental applications, and low cost compared with other electroanalytical methods that have been reported for the quantification of picric acid. Additionally, the possibility to develop an in situ device for the detection of picric acid using a disposable sensor was evaluated.

The use of a gold disc microelectrode for the determination of copper in human sweat

A novel approach of using a gold disc microelectrode to analyze sweat samples for copper ions by anodic square wave stripping voltammetry (SW stripping voltammetry) is described. Sweat was collected from the lower back of four subjects after physical exercise and the sample volume required for the determinations was 100 μL. Under the optimized conditions, the calibration plot was linear over the range 1-100 μmol L(-1) Cu(II) with a limit of detection of 0.25 μmol L(-1). The precision was evaluated by carrying out five replicate measurements in a 1 μmol L(-1) Cu(II) solution and the standard deviation was found to be 1.5%. Measurements were performed by inserting the microelectrode into sweat drops and Cu(II) concentrations in the analyzed samples ranged from 0.9 to 28 μmol L(-1). Values obtained by the proposed voltammetric method agreed well with those found using graphite furnace atomic absorption spectroscopy (GFAAS).

Development of a Molecularly Imprinted Modified Electrode to Evaluate Phenacetin Based on the Preconcentration of Acetaminophen

A glassy carbon electrode modified with a molecularly imprinted polymer (MIP) containing phenacetin recognition sites is introduced. The phenacetin-selective MIP was synthesised based on the electropolymerisation of pyrrole in a 1:1 (v/v) water/ethanol with HClO4 solution. The MIP-modified electrode showed higher recognition ability in comparison with a bare electrode for procaine and aminopyrine, reported to electrochemically interfere in the quantification of phenacetin in cocaine samples. In addition, the MIP was able to preconcentrate one of the intermediates of the phenacetin electrochemical oxidation, acetaminophen, indicating the possibility of monitoring phenacetin based on the acetaminophen oxidation. The acetaminophen oxidation peak is 15 times more detectable compared to the signal obtained by the non-molecularly imprinted polymer (NIP), and it occurs 450 mV below the phenacetin electrochemical oxidation signal. These achieved characteristics decrease the possibility of interference from other electrochemical reactions that may occur in the same potential range as phenacetin electrochemical process.

INVESTIGAÇÃO DO USO DE ELETRODO DE CARBONO VÍTREO MODIFICADO COM HEXACIANOFERRATO DE RUTÊNIO PARA DETECÇÃO DE PROCAÍNA

A glassy carbon electrode modified with ruthenium hexacyanoferrate (RuOHCF) was investigated as an electrocatalyst for the detection of procaine with the aim of quantification in pharmaceutical and forensic samples. The RuOHCF films were prepared by electrochemical deposition, and the parameters used in this process (concentration of RuCl3, K3Fe(CN)6, temperature, and number of cyclic voltammograms recorded in the modification step) were carefully optimized. Based on the optimal conditions achieved, the RuOHCF modified electrode allows the determination of procaine at 0.0 V with a detection limit of 11 nmol L-1using square wave voltammetry.

Determinação de ácido acéttico em amostra de vinagre adulterada com ácido clorídrico - um experimento integrado de titulação potenciométrica e condutométrica

The determination of acetic acid in vinegar adulterated sample using simultaneous potentiometric and condutometric titrations was used as an example of integrated experiment in instrumental analysis. An Excel® spreadsheet, which allows the entry of simultaneous data and the construction of the superimposed experimental curves (condutometric, potentiometric, first and second derivative potentiometric curve and, distribution diagrama of the acetic species as function of pH), was used as powerful tool to discuss the fundamental concepts involved in each technique and choose the best of them to quantify, without mutual interference, H3CCOOH and HCl in vinegar adulterated sample.

CHAPTER 7:Application of Pattern Recognition Techniques in the Development of Electronic Tongues

The human tongue, by virtue of the biological receptors present on it, is capable of recognizing five basic tastes: sweetness, saltiness, bitterness, sour, and umami. Likewise, an electronic tongue is a device with synthetic receptors that can distinguish different samples into patterns as a result of the different responses or information extracted from each sample. To perform pattern recognition using an electronic tongue, mathematical tools are required. Hence, chemometric analysis, particularly principal component analysis (PCA), is used for this purpose. PCA is used to represent all data obtained from an electronic tongue using a smaller number of new variables than those in the original data, and representing this new information in 2D or 3D plots. This chapter describes the concept of an electronic tongue, the manner in which PCA is employed to mimic the pattern recognition that occurs in the brain when using the human tongue as a biological receptor, and some applications of such electronic devices for beverage analysis.