Desenvolvimento de eletrodo de pasta de carbono modificado com biocarvão de tucumã para determinação de quinolina em amostras de efluentes por meio de técnicas voltamétricas

Abstract

Quinoline is an organic chemical substance belonging to the class of alkaloids and can be found in plants. This molecule is employed in the synthesis of pharmaceuticals and agricultural pesticides. However, it possesses high toxicity when in contact with humans, potentially causing liver and kidney diseases in addition to presenting significant environmental risks. Nonetheless, due to its use by the industrial sector in the development of various products, this substance can be detected in industrial waste, resulting in the contamination of soils, rivers, and groundwater. Therefore, the determination of quinoline in effluent samples is essential, given its risk to ecosystems. One method for determining quinoline is through voltammetric techniques, a set of electroanalytical techniques that generate low waste, are relatively inexpensive, and versatile. Due to their versatility, modifications can be made to electrochemical sensors for the determination of substances with greater sensitivity and selectivity. The present study aimed to develop a carbon paste electrode modified with tucumã biochar for the determination of quinoline in textile effluents. For this, the proportion of the carbon paste was optimized, and the best response was obtained with the paste proportion of 40:30:30 (graphite: tucumã biochar: binder). The electrochemical system consisted of an electrochemical cell containing 10 mL of BR buffer solution 0.02 mol L⁻¹ in ammonium chloride (NH₄Cl) 0.5 mol L⁻¹ support electrolyte, with pH 2. The electrodes used were the carbon paste electrode modified with tucumã biochar (EPCM/BT), the Ag|AgCl reference electrode, and the platinum wire auxiliary electrode. For the determination of quinoline, the influence of pH and the parameters of the differential pulse voltammetry technique were investigated. Thus, analytical curves were constructed in the absence and presence of matrix (textile effluent), and three different effluents were tested. The curve prepared in the absence of effluent showed a concentration range of 3.00x10⁻⁷ to 9x10⁻⁷ mol L⁻¹ of quinoline and demonstrated r² equal to 0.995, in addition to showing a LOD equal to 2.32 µmol L⁻¹ and LOQ of 7.73 µmol L⁻¹. The curves constructed in the presence of textile effluent presented r² equal to 0.994, 0.996, and 0.992 for effluents 1, 2, and 3 respectively. The limits of detection for effluents 1 to 3 were 3.28, 2.48, and 8.26 nmol L⁻¹, while the limits of quantification for the same samples were 5.46, 0.3648, and 1.22 nmol L⁻¹. The matrix effects (ME) were also calculated for each analytical curve, and effluents 2 and 3 presented high matrix effect, while effluent 1 demonstrated medium ME. The standard deviation values (n=10) for repeatability and reproducibility tests remained close to 100%. Finally, quinoline recovery ranged from 98 to 100%, indicating that the determination of quinoline in textile effluent samples by the developed method was successful.