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Ultrasound-assisted extraction and direct analysis were compared with total digestion for magnesium determination in beer samples by flame atomic absorption spectrometry. The method for total digestion used concentrated nitric acid under plate heating. In optimized instrumental conditions, validation of the analytical method was promoted, with good linear range (0.06 to 0.5 mg L�1), low limits of detection and quantification (0.04 and 0.12 �g g�1, respectively), good precision, relative standard deviation (RSD) less than 3.4%, and accuracy (recovery levels of 91.5 to 99.0%). The characteristic concentration (C0) was 9 �g L�1. The extraction procedure was performed in a 1:1 nitric acid solution for 55 min in an ultrasonic bath at 60 �C, while the direct analysis involved a dilution of the samples in a 2% v/v nitric acid solution. The different sample preparation methods were applied to 13 beer samples and at a 95% confidence level, no significant differences were observed. Thus, direct analysis proved to be more suitable for quality control routines of beer samples in the industry.

In this work, the batch injection analysis system with amperometric detection using reduced graphene oxide as a modifier of glassy carbon electrode (GCE) was investigated for the simple, fast, and sensitive monitoring of levofloxacin (LEVO) and ciprofloxacin (CIPRO) in samples of pharmaceutical formulations, synthetic urine, and milk (low- and high-fat content). LEVO and CIPRO were quantified in seven samples using amperometric measurements at +1.10 V vs Ag/AgCl, KCl(sat). The developed methods showed excellent analytical performance with limits of detection of 0.30 and 0.16 μmol L−1, linear range from 3.0 to 50 μmol L−1 and 1.0 to 50 μmol L−1, relative standard deviation below 9.7 and 3.1%, and recovery ranges ranging from 80 to 107% and from 78 to 109% for LEVO and CIPRO, respectively. In addition, the minimum sample preparation (simple dilution) combined with a high analytical frequency (130 to 180 analyses per hour) can be highlighted. Thus, the methods are promising for implementation in routine analysis and quality control to different samples.

In this paper, we compare reduced graphene oxide (RGO) electrode with multi-walled carbon nanotubes (MWCNT) as modifiers for the sensitive detection of levofloxacin. The RGO-based sensor showed higher currents for levofloxacin compared with the MWCNT-modified (4-fold) and unmodified electrodes (20-fold). A thin-layer adsorptive process was verified for the oxidation of levofloxacin on the RGO-modified electrode which explains the higher currents. Differential pulse voltammetry (DPV), square wave voltammetry (SWV), and amperometric detection using flow-injection analysis (FIA-AMP) were evaluated for levofloxacin determination in urine and pharmaceutical samples. Detection limits of 1.45, 6.70, and 1.90 μmol L−1 and recovery levels of 91, 106, and 103%, respectively were obtained. A relative standard deviation lower than 7.7% indicated proper precision. The FIA-AMP using the RGO-modified electrode presented high analytical frequency (around 100 injections per hour) and thus was selected for the analysis of the samples. Statistically, similar results (95% confidence level) compared with ultra-fast liquid chromatography (UFLC) analysis and recovery level of 96% for the analysis of urine were obtained.

Neste trabalho, foi comparado óxido de grafeno reduzido (OGR) e nanotubos de carbono de paredes múltiplas (MWCNT) como modificadores da superfície do eletrodo de carbono vítreo para a determinação de levofloxacina. Ambos nanomateriais foram devidamente caracterizados por espectroscopia Raman, mostrando assim que de fato houve mudanças estruturais após a funcionalização. Experimentos envolvendo a voltametria cíclica, mostraram que o sensor a base de RGO apresentou maior ganho de sinal analítico para a levofloxacina em comparação com os eletrodos modificados com MWCNT (4 vezes) e sem modificação (20 vezes). O processo de oxidação da levofloxacina sobre as diferentes superfícies eletródicas foi controlado pela adsorção das espécies eletroativas e irreversível em aproximadamente + 1,0 V. Voltametria de pulso diferencial (VPD), voltametria de onda quadrada (VOQ), detecção amperométrica usando análise por injeção em fluxo (FIA-AMP) e por injeção em batelada (BIA-AMP) foram avaliadas para determinação da levofloxacina em amostras de formulações farmacêuticas, utilizando o eletrodo modificado com OGR. Os métodos desenvolvidos apresentaram limites de detecção de 1,45; 6,70; 1,90; 0,33 µmol L-1 e níveis de recuperação de 91, 106, 103 e 101 %, respectivamente. Todos os desvios padrão relativos foram inferiores a 7,0 %, indicando precisões adequadas. Os teores de levofloxacina foram concordantes com o valor estabelecido pelo fabricante do medicamento. Para análise da amostra de urina, os métodos dinâmicos FIA/BIA-AMP foram selecionados devido a elevada frequência analítica (cerca de 100 injeções por hora), sendo obtido um nível de recuperação entre 96-98%. Todos os resultados eletroquímicos foram estatisticamente comparáveis com a análise por cromatografia líquida ultra-rápida (UFLC), à um nível de 95 % de confiabilidade, demonstrando que os métodos são promissores para análises de rotina. In this work, reduced graphene oxide (OGR) and multi-walled carbon nanotubes (MWCNT) were compared as glass-carbon electrode surface modifiers for the determination of levofloxacin. Both nanomaterials were properly characterized by Raman spectroscopy, thus showing that there were in fact structural changes after functionalization. Experiments involving cyclic voltammetry, showed that the rGO-based sensor showed greater analytical signal gain for levofloxacin compared to electrodes modified with MWCNT (4 times) and without modification (20 times). The oxidation process of levofloxacin on the different electrode surfaces was controlled by the adsorption of the electroactive and irreversible species at approximately + 1.0 V. Differential pulse voltammetry (VPD), square wave voltammetry (VOQ), amperometric detection using injection analysis flow (FIA-AMP) and batch injection (BIA-AMP) were evaluated to determine levofloxacin in samples of pharmaceutical formulations using the rGO modified electrode. The developed methods presented detection limits of 1.45; 6.70; 1.90; 0.33 µmol L-1 and recovery levels of 91, 106, 103 and 101%, respectively. All relative standard deviations were less than 7.0 %, indicating adequate precision. Levofloxacin levels were in agreement with the value established by the drug manufacturer. For analysis of the urine sample, the dynamic methods FIA / BIA-AMP were selected due to the high analytical frequency (about 100 injections per hour), with a recovery level between 96-98%. All electrochemical results were statistically comparable with the analysis by ultra-fast liquid chromatography (UFLC), at a level of 95% reliability, demonstrating that the methods are promising for routine analysis.

In this paper, a simple, sensitive and precise electroanalytical method was developed using flow injection analysis (FIA) with amperometric detection and reduced graphene oxide sensor for ascorbic acid determination in samples of multivitamin beverages, milk, fermented milk, and milk chocolate. The advantages of this sensor include a potential displacement of 450 mV and a 2-fold peak current increase for electrochemical oxidation of ascorbic acid, which resulted in a highly sensitive method. No interference of sample matrix was observed, avoiding solvent extraction procedures (samples were only diluted). The FIA allowed a high analytical frequency, approximately 96 injections per hour, together with adequate detection limit of 4.7 μmol L−1. Good precision (RSD