Contaminants of emerging concern (CECs) are chemicals, including pharmaceutical and personal care products, not commonly monitored in the aquatic environment. Pharmaceuticals are nowadays considered as an important environmental contaminant. Chromatography methods which require expensive equipment and complicated sample pretreatment are used for detection of CECs in natural water. Thus, in this study we proposed a simple, fast, and low-cost voltammetric method as a screening tool for the determination of CECs in natural water prior to chromatography. A case study was conducted with alprazolam (benzodiazepine). The method was optimized and validated in-house. The limit of quantification was 0.4 μg L(-1) for a 120 s preconcentration time. The recoveries ranged from 93 to 120 % for accuracy tests. A further proposal aim was to determine for the first time the occurrence of alprazolam in Brazilian river water and to evaluate its potential use as a marker of contamination by wastewater.
17α-Ethinyl estradiol (EE2), which is used worldwide in the treatment of some cancers and as a contraceptive, is often found in aquatic systems and is considered a pharmaceutically active compound (PhACs) in the environment. Current methods for the determination of this compound, such as chromatography, are expensive and lengthy and require large amounts of toxic organic solvents. In this work, a voltammetric procedure is developed and validated as a screening tool for detecting EE2 in water samples without prior extraction, clean-up, or derivatization steps. Application of the method we elaborate here to EE2 analysis is unprecedented. EE2 detection was carried out using differential pulse adsorptive cathodic stripping voltammetry (DP AdCSV) with a hanging mercury drop electrode (HMDE) in pH 7.0 Britton-Robinson buffer. The electrochemical process of EE2 reduction was investigated by cyclic voltammetry at different scan rates. Electroreduction of the hormone on a mercury electrode exhibited a peak at −1.16 ± 0.02 V versus Ag/AgCl. The experimental parameters were as follows: −0.7 V accumulation potential, 150 s accumulation time, and 60 mV s−1 scan rate. The limit of detection was 0.49 μg L−1 for a preconcentration time of 150 s. Relative standard deviations were less than 13%. The method was applied to the detection of EE2 in water samples with recoveries ranging from 93.7 to 102.5%.
The differential pulse adsorptive cathodic stripping voltammetry (DP-AdsCSV) employing the hanging mercury drop electrode (HMDE) was used towards the determination of two psychotropic drugs in environmental samples. Voltammetric and experimental conditions to Clonazepam (CLO) and diazepam (DIAZ) were optimized and the methods were in-house validated. Accumulation potentials were À0.3 V to CLO and À0.6 V to DIAZ at 120 s of accumulation time. Pulse amplitude, pulse time and scan rate were 80 mV, 20 ms and 25 mV s À1to CLO and 100 mV, 20 ms and 40 mV s À1 to DIAZ, respectively. Recovery tests were done in three different concentrations to evaluate methods' accuracy and the results were from 88 AE 6 to 120 AE 13 %. In precision tests, standard deviations were lower than 15 % for both methods. Goods limits of quantification 0.65 and 0.27 mg L À1 to CLO and DIAZ respectively were achieved without pre-concentration steps such as SPE, etc. Voltammetry employing HMDE was first used for the determination of CLO and DIAZ in natural water. Natural samples were spiked and recovery tests confirmed the applicability of the methods developed. Nine samples from Parana state, Brazil, were analyzed and CLO and DIAZ values were below the limits of detection in all samples.
THE VERSATILITY OF THE HANGING MERCURY DROP ELECTRODE IN ANALYTICAL CHEMISTRY -A REVIEWABOUT RECENT APPLICATIONS. Voltammetry using mercury electrode as working electrode has been employed in the determination of organic and inorganic compounds in several samples. A review on the applications of this analytical tool is present, covering the period of the last ten years. The emphasis of this work is directed to the hanging mercury drop electrode (HMDE), its advantages, disadvantages and applications. Voltammetric measurements are easily carried out, and present low cost. The review discusses that the use of mercury in the measurements can be a limitation due the toxicity of the element. However, nowadays the necessary of volume of Hg in the measurements is very small, and it can be reused. Thus, the correct disposal of the small amount of waste generated can be minimize environmental risks and human health, according to the principles of Green Chemistry.Keywords: applications; mercury electrode; review; voltammetry. INTRODUÇÃOTécnicas eletroquímicas têm sido usadas por muitos anos devido as suas características vantajosas, tais como elevada frequência analí-tica, simplicidade, baixo custo, capacidade de detecção em níveis de concentração baixa, resposta dependente das formas químicas de um mesmo elemento, análise de misturas, entre outras. Os primeiros estudos eletroquímicos iniciaram no século XVIII na Itália e evoluíram até os métodos atuais, envolvendo diversos tipos de eletrodos indicadores e de trabalho, como eletrodos sólidos, de mercúrio, ultramicroeletrodos, etc.1-4 Cada tipo de eletrodo desenvolvido possui vantagens e desvantagens intrínsecas. Eletrodos de trabalho sólidos, por exemplo, apresentam como vantagem a possibilidade de serem modificados, aumentando assim sua seletividade, além de possuírem diversas formas e tamanhos que ampliam sua aplicabilidade. Entretanto, processos de limpeza e polimento são comumente necessários devido ao envenenamento da superfície eletrolítica, que podem comprometer a reprodutibilidade de sua área superficial. O eletrodo de gota pendente de mercúrio, do inglês hanging mercury drop electrode (HMDE), por sua vez, por ser renovável apresenta excelente reprodutibilidade, uma superfície extremamente lisa e uniforme a cada gota. Além disso, um elevado sobrepotencial à redução de hidrogênio, uma ampla faixa negativa de potencial (de 0 a -2 V dependendo do eletrólito suporte) assim como a superfície reprodutível a cada gota, são vantagens deste eletrodo.5 Entretanto, o HMDE apresenta baixa resistência mecâni-ca, limitando suas aplicações, bem como relativa seletividade para compostos orgânicos, pode sofrer com interferências causadas por matéria orgânica dissolvida em amostras ambientais, estreita faixa de trabalho na região anódica, etc. Além disso, muitas discussões vêm sendo realizadas com relação à toxicidade do mercúrio e a necessidade de buscar materiais alternativos para o desenvolvimento de outros eletrodos de trabalho mais condizentes com os aspectos de Química Verde. ...
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