Leonardo Luiz Okumura

Determinação de zinco em álcool combustível opr voltametria de redissolução anódica

The presence of heavy metals in fuel ethanol is obtained in different steps as production and storage of ethanol, constituting an inorganic contamination. Quantitative analysis of these contaminants has been usually carried out by conventional techniques as atomic absorption spectrofotometry. According to high sensibility of stripping voltammetric techniques for quantification of heavy metals and a few number of realized works for this kind of matrix, the aim of this work was to develop an electroanalytical procedure for zinc determination in fuel ethanol. Electrochemical determination for zinc in aqueous media by linear sweep voltammetry exhibited an anodic peak current in a potential of -1,12V vs. SCE, presenting linear dependence against zinc concentration in an interval of 5,0x10-7 to 5,0x10-6 mol.L-1 with an amperommetric sensibility of 1,2x106 mA.mol-1.L and a detection limit of 2,6x10-7 mol.L-1. Zinc determination in fuel ethanol commercial sample was obtained by addiction of 200 mL of sample in a final volume of 20 mL of supporting electrolite. The concentration of zinc in the sample was obtained by standard addiction method, presenting a value of 5,7± 0,19x10-5 mol.L-1 in zinc.

Simultaneous determination of neutral nitrogen compounds in gasoline and diesel by differential pulse voltammetry

The presence of trace neutral organonitrogen compounds as carbazole and indole in derivative petroleum fuels plays an important role in the cars engine maintenance. In addition, these substances contribute to the environmental contamination and their control is necessary because most of them are potentially carcinogenic and mutagenic. For those reasons, a reliable and sensitive method was proposed for the determination of neutral nitrogen compounds in fuel samples, such as gasoline and diesel using preconcentration with modified silica gel (Merck 70-230 mesh ASTM) followed by differential pulse voltammetry (DPV) technique on a glassy carbon electrode. The electrochemical behavior of carbazole and indole studied by cyclic voltammetry (CV) suggests that their reduction occurs via a reversible electron transfer followed by an irreversible chemical reaction. Very well resolved diffusion controlled voltammetric peaks were obtained in dimethylformamide (DMF) with tetrabutylammonium tetrafluoroborate (TBAF(4) 0.1molL(-1)) for indole (-2.27V) and carbazole (-2.67V) versus Ag|AgCl|KCl(sat) reference electrode. The proposed DPV method showed a good linear response range from 0.10 to 300mgL(-1) and a limit of detection (L.O.D) of 7.48 and 2.66mugL(-1) for indole and carbazole, respectively. The results showed that simultaneous determination of indole and carbazole presents in spiked gasoline samples were 15.8+/-0.3 and 64.6+/-0.9mgL(-1) and in spiked diesel samples were 9.29+/-1 and 142+/-1mgL(-1), respectively. The recovery was evaluated and the results shown the values of 88.9+/-0.4 and 90.2+/-0.8% for carbazole and indole in fuel determinations. The proposed method was also compared with UV-vis spectrophotometric measures and the results obtained for the two methods were in good agreement according to the F and t Students tests.

Electroanalysis and determination of acetaldehyde in fuel ethanol using the reaction with 2,4-dinitrophenylhydrazine

The voltammetric reduction of acetaldehyde was studied in 0.1 M LiOH: LiCl (60: 40 v/v). Well-defined waves can be seen at −1.77 and −1.60 V with the use of hanging mercury and glassy carbon electrodes. Acetaldehyde was shown to react at room temperature with the 2,4-dinitrophenylhydrazine and the product exhibited a differential pulse voltammetric peak at −0.90 V, which was well separated from the peaks of the derivative. This allowed the indirect determination of acetaldehyde in the presence of 0.1 M ethanol/tetrabutylammonium perchlorate after 10 min of reaction. Calibration graphs were obtained for 1.00 × 10−6−1.00 × 10−4 M of acetaldehyde. The detection limit is 8.14 × 10−7 M. The method has been applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pretreatment.

Avaliação do método das adições de analito para a determinação de sódio em álcool combustível por espestrometria de emissão atômica em chama

O metodo empregado para a determinacao de sodio por espectrometria de emissao atomica em chama, foi o das adicoes de analito sendo as intensidades de emissao representadas em funcao das concentracoes de analito adicionadas as varias porcoes da amostra, numa faixa linear de 0 - 0,300 mg Na L-1, empregando-se 2,1 g K L-1 como supressor de ionizacao. Foram analisadas 20 amostras comerciais de alcool etilico hidratado combustivel (AEHC), coletadas em diferentes postos de abastecimento, na cidade de Araraquara e os resultados obtidos encontram-se no intervalo, desde menor que o limite de deteccao (0,0072 mg Na L-1) ate 1,55 mg Na L-1. Os limites de deteccao referentes a determinacao de sodio em cada amostra situam-se entre 0,0026 e 0,0239 mg Na L-1. A porcentagem de recuperacao variou no intervalo de 95 a 104 %. Os desvios padrao relativos (n=12) foram £ 4,1 % para as tres adicoes de analito, nas 20 amostras de AEHC.

Comportamento voltamétrico da redução de 2-furfuraldeído em etanol utilizando eletrodo de carbono vítreo

This study reports the electrochemical behavior of 2-furfuraldehide reduction in ethanol using glassy carbon electrode, aiming to correlate adequate experimental conditions for determination of this 2-furfuraldehide in fuel ethanol. Obtained voltammograms for 2-furfuraldehide in a scan rate of 100mV.s-1 present a cathodic peak current in a potential of -1,45V vs. SCE for aqueous medium and -1,71V vs. SCE for alcoholic medium, being observed no anodic currents in these reactional media. The relation of ipc with v1/2 showed linear behavior in both media, exhibiting a mass transport controlled by diffusion. The analysis of electrochemical parameters obtained in this work has exhibited an irreversible behavior for the electrodic process. The dependence of cathodic peak current against concentration showed linearity in the interval of 9,5x10-4 to 5,8x10-3 mol L-1 for both media. The sensitivity of method on the aqueous and alcoholic medium was 13,4 and 13,0 (x 10-3) mA mol-1 L respectively. The limits of detection (L.D.) for 2-furfuraldehide, on the aqueous and alcoholic medium was 0,70 e 0,80 (x 10-3) mol L-1 respectively.

New Voltammetry-Based Technique for the Determination of Tebuthiuron in Crystal and Brown Sugar Samples

O acucar e amplamente consumido em todo o mundo e o Brasil e o maior produtor, consumidor e exportador deste produto. Para garantir o bom desenvolvimento e produtividade das culturas de cana de acucar, e necessario aplicar grandes quantidades de agrotoxicos, principalmente herbicidas e pesticidas. O herbicida tebuthiuron (TBH) impede a pre e pos-emergencia das plantas daninhas infestantes nas culturas de cana de acucar. Considerando que e importante para garantir a seguranca alimentar da populacao, este trabalho propoe um metodo confiavel para analisar TBH em matrizes de acucar (mascavo e cristal), usando voltametria de onda quadrada (SWV) e voltametria de pulso diferencial (DPV) em eletrodo de carbono vitreo e investigar o comportamento eletroquimico do herbicida por voltametria ciclica (CV). Os nossos resultados sugerem que TBH ou o produto da sua reacao com o eletrolito de suporte e oxidado atraves da transferencia irreversivel de um eletron entre o analito e eletrodo de trabalho, a um potencial de cerca de +1,16 V vs. Ag|AgClsat em 0,10 mol L-1 KOH como solucao de eletrolito de suporte. Tanto DPV quanto SWV sao satisfatorios para a analise quantitativa do analito. DPV e mais sensivel e seletiva, com limites de deteccao de 0,902, 0,815 e 0,578 mg kg-1, e limite de quantificacao de 0,009, 0,010 e 0,008 mg kg-1, na ausencia da matriz, e na presenca de matriz de acucar cristal e mascavo, respectivamente. Reprodutibilidade situou-se entre 0,53 e 13,8%, a precisao variou entre 4,14 e 15,0%, e a recuperacao manteve-se entre 84,2 e 113% para DPV conduzido na ausencia e na presenca da matriz de acucar cristal, respectivamente.

Quantification of Arsenic in Sugar Cane Brandy of Minas Gerais Using Carbon Paste Electrode Modified with Carbon Nanotubes

An eletroanalytical method for determination of arsenic in sugar cane brandy using an electrode consisting of carbon paste modified with carbon nanotubes (CNTPE) and mineral oil has been developed. The cyclic (CV) and linear sweep voltammetry modes (LSV) with cathodic stripping were employed for CNTPE containing mineral oil. The analytical curves were linear from 30.0 to 80.0 µg L -1 for LSV. The limit of detection (L.O.D.) was 10.45 μg L -1 and limit of quantification (L.O.Q.) was 34.33 μg L -1 . The developed method was applied to the determination of arsenic in tree commercial sugar cane brandy samples. The results were in good agreement with those obtained by HGAAS, showing that CNTPE containing mineral oil can be successfully employed to the simultaneous determination of arsenic in sugar cane brandy samples.

Adsorptive Stripping Voltammetric Determination of Oxolinic Acid in Water Sample

One new methodology for analysis of the antimicrobial oxolinic acid (OXA) based on adsorptive stripping voltammetry (AdSV) in carbon paste electrode (CPE) was developed and applied in untreated pond water sample. Cyclic voltammetry (CV) indicated that an irreversible anodic process occurs in KOH solution as supporting electrolyte. Quantification of the antimicrobial was carried out by differential pulse adsorptive stripping voltammetry (DPAdSV) at potential of deposition (ED) +1.05 V for 45 s to examine OXA adsorption on the surface of CPE. The limits of detection (LOD) and quantification (LOQ) of the method for OXA analysis were determined. The values of LOD were 0.0570 and 0.512 mg L in absence of matrix and in the water sample, respectively, and the corresponding values of LOQ were 0.192 and 1.707 mg L, respectively. The apparent recovery percentage for different concentrations of OXA in natural waters ranged between 98.4 and 109%.

SENSITIVE MULTIRESIDUE QUANTIFICATION OF PROCYMIDONE AND TEBUTHIURON ON CARBON PASTE ELECTRODE BY DIFFERENTIAL-PULSE VOLTAMMETRY

Qualitative electrochemical characterization of procymidone (PRO) and tebuthiuron (TBH) was carried out by cyclic voltammetry using a carbon paste electrode. The studies suggest that analyte mass transfer is controlled by diffusion, and that oxidation of PRO and TBH occurs by means of irreversible electronic transfer of one electron. Oxidation of PRO and TBH occurs close to +0.820 V and +1.075 V (vs. Ag|AgCl, KCl 3.0 mol L -1), respectively, in a 0.10 mol L–1 KOH solution as supporting electrolyte. Quantitative analyses were carried out by differential-pulse voltammetry, a technique which is more sensitive and selective. Detection and quantification limits were determined for PRO and TBH in the absence of matrix, in a potable-water matrix, and in a nonpotable-water matrix, for which the ranges of reproducibility, intermediate precision and recovery rates were (1.01 and 4.20 %), (4.08 and 9.56 %), and (90.6 and 115 %) for PRO, and (1.59 and 3.92 %), (4.84 and 7.46 %), and (91.3 and 119 %), for TBH, respectively. The results indicate that the new method is selective, simple and cheap to simultaneously quantify PRO and TBH in water samples.

Carbon Paste Electrode Modified with Ascorbic Acid and Carbon Nanotubes for Determination Copper in Sugar Cane Spirit

This work has been carried out in order to determine the copper content in sugar cane spirit samples from the south of Minas Gerais, using a carbon paste electrode modified with ascorbic acid and carbon nanotubes using the square wave voltammetry technique. The following parameters were studied: Ed (deposit potencial). Td (deposit time), f (frequency), A (amplitude) and Es (increment scanning). The analytical curve was built in an interval from 0.5 to 12 mg L -1 and a coefficient of linear correlation of 0.997 Three sugar cane spirit samples were analysed, which presented copper content ranging from 0.29 to 1.59 mg L -1 .