Thallium (Tl) is a rare metal with toxic effects notably harmful to human health and the environment. In this article, the natural occurrence of Tl was evaluated in a deactivated manganese mine located in the western region of Bahia, Brazil. The extraction procedure with aqua regia was used to dissolve the soil, sediment, and tailings samples. The Tl content was determined by differential pulse anodic stripping voltammetry (DPASV) and manganese (Mn) and iron (Fe) by flame atomic absorption spectroscopy (FAAS). The Tl levels ranged from 0.64 to 473 mg kg-1, triggering an alert since most of the samples (soil and sediment) analyzed presented Tl concentrations above 1.0 mg kg-1, recognized as the maximum limit recommended by environmental agencies in North America and Europe.

The use of a palladium film electrode (PdFE) as an alternative electrode for the determination of thallium (Tl+) and lead (Pb2+) in water samples by anodic stripping voltammetry is proposed. Preliminary studies of the influence of the substrate were performed on the electrochemical behavior of PdFE prepared ex situ. Using a silver solid amalgam electrode as substrate (AgSAE), the effect of several parameters such as potential and deposition time, composition and pH of supporting electrolyte on the analytical response of PdFE for Tl+ by differential pulse anodic stripping voltammetry (DPASV) was initially investigated. Under best experimental conditions of deposition potential of −1.2 V and deposition time of 300s the analytical curve was linear in the Tl+ concentration from 3.0 to 100.0 µg L−1 with a relative standard deviation (RSD) <2.0%. The limit of detection (LOD) and limit of quantification (LOQ) were 0.89 µg L−1 and 2.96 µg L−1, respectively. The PdFE was successfully applied for the determination of Tl+ in water samples. Moreover, this electrode showed promising as a sensor for the simultaneous determination of Tl+ and Pb2+ and as a suitable alternative to the mercury electrode.

A webcam is proposed as the detector in a flow system with multicommutation, and the feasibility of the approach is demonstrated in the determination of nitrate and nitrite in natural waters. The typical transient signal inherent to the flow system was obtained using a digital video and quantified by ImageJ software. The linear dynamics range for nitrite and nitrate determinations were 0.2 to 2.0 mg L-1 NO2− and 1.0 to 10.0 mg L-1 NO3−, with relative standard deviation < 2% for both analytes. The limits of detection were 0.01 and 0.04 mg L-1 for nitrite for nitrate, respectively, and the sampling rate were 80 and 103 h-1 for nitrite and nitrate, respectively. The use of webcams has a high potential for analysis in the visible region of the electromagnetic spectrum, and the proposed strategy constitutes a promising alternative to traditional absorbance measurements that depend on conventional equipment. The webcam detection system is attractive, especially in relation to field analysis.

A flow injection chemiluminescence method for the determination of paracetamol in pharmaceutical formulations is described. It is based on the consumption of the sodium hypochlorite by paracetamol and decreases of the analytical signal. The analytical curve was linear in the paracetamol concentration range from 5.0 x 10-6 to 5.0 x 10-5 mol L-1, with a detection limit of 1.8 x 10-6 mol L-1. The RSDs were 2.0 and 1.2% respectively for 2.0 x 10-5 and 4.0 x 10-5 mol L-1 paracetamol solutions (n = 10) and a sampling frequency of 180 h-1 was obtained.

In this work we describe both a chromatographic purification procedure and a spot test for the enzyme peroxidase (POD: EC 1.11.1.7). The enzyme was obtained from crude extracts of sweet potatoes and the chromatographic enzyme purification procedure resulted in several fractions. Therefore a simple, fast and economic spot test for monitoring peroxidase during the purification procedure was developed. The spot test is based on the reaction of hydrogen peroxide and guaiacol, which is catalyzed by the presence of peroxidase yielding the colored tetraguaiacol.

Um biossensor de pasta de carbono modificado com extrato bruto enzimático do fungo Pleurotus ostreatus como fonte de lacase é proposto para a determinação de catecolaminas em formulações farmacêuticas. Essa enzima catalisa a oxidação de adrenalina ou dopamina nas quinonas correspondentes e a corrente obtida na redução eletroquímica de cada um dos produtos é relacionada a concentração dessas catecolaminas em solução da amostra. O efeito da concentração de lacase de 0,29 a 1,8 U/mg de pasta de carbono, do pH de 3,0 a 8,0, da velocidade de varredura de 10 a 40 mV s-1 e amplitudes de pulso de potencial de 10 a 60 mV sobre a resposta voltamétrica de pulso diferencial foi investigado. O desvio padrão relativo foi menor que 1,8% para solução de hidroquinona 2,8 x 10-4 mol L-1 em pH 7 (n=10). Recuperações variando de 97,3 a 101% para adrenalina e de 95,8 a 102% para dopamina foram obtidas. As curvas analíticas foram lineares no intervalo de concentração de adrenalina de 6,0 x 10-5 a 7,0 x 10-4 mol L-1 e de 7,0 x 10-5 a 4,0 x 10-4 mol L-1 para dopamina, com limites de detecção de 7,9 x 10-6 mol L-1 e 9,8 x 10-6 mol L-1, respectivamente. Esse biossensor foi empregado para a determinação de adrenalina e dopamina em formulações farmacêuticas. Os resultados obtidos com o biossensor para a determinação dessas catecolaminas em formulações farmacêuticas estão em concordância a um nível de confiança de 95% com o procedimento da Farmacopéia americana.

A carbon paste biosensor modified with a crude enzymatic extract of the Pleurotus ostreatus fungi as a laccase source is proposed for catecholamine determination in pharmaceutical formulations. This enzyme catalyzes the oxidation of adrenaline or dopamine in the corresponding quinones and the current obtained in the electrochemical reduction of each of the products is related to the concentration of these catecholamines in the sample solution. The effect of the laccase concentration from 0.29 to 1.8 U/mg of carbon paste, pH from 3.0 to 8.0, scan rate from 10 to 40 mV s-1 and potential pulse amplitude from 10 to 60 mV on the differential pulse voltammetric response was investigated. The relative standard deviation was smaller than 1.8% for a 2.8 x 10-4 mol L-1 hydroquinone solution at pH 7.0 (n=10). Recoveries varied from 97.3 to 101% for adrenaline and from 95.8 to 102% for dopamine. The analytical curves were rectilinear in the adrenaline concentration range from 6.0 x 10-5 to 7.0 x 10-4 mol L-1 and 7.0 x 10-5 to 4.0 x 10-4 mol L-1 for dopamine, with detection limits of 7.9 x 10-6 mol L-1 and 9.8 x 10-6 mol L-1, respectively. This biosensor was used for adrenaline and dopamine determinations in pharmaceutical formulations. The results obtained using the proposed biosensor are in close agreement with those obtained using an American Pharmacopoeia procedure at a 95% confidence level.