Voltammetric determination of total iron in fuel ethanol using a 1,10 fenantroline/nafion carbon paste-modified electrode

This work presents a methodology for iron determination in fuel ethanol using a modified carbon paste electrode with 1.10 fenantroline/nafion. The electrochemical parameters were optimized for the proposed system and the voltammetric technique of square wave was employed for iron determination. An accumulation time of 5 minutes, such as a 100 mV of pulse magnitude (E(sw)) and frequency (f) of 25 Hz were used as optimized experimental conditions. The modified carbon paste electrode presented linear dependence of amperometric signal with iron concentration in a work range from 6.0x10(-6) until 2.0x10(-5) mol L(-1) of iron, exhibiting a linear correlation coefficient of 0.9884, a detection limit of 2.4 x10(-6) mol L(-1) (n = 3) and amperometric sensibility of 4.5x10(5) mu A/mol L(-1). Analytical curve method was used for iron determination at a commercial fuel sample. Flame atomic absorption spectroscopy was employed as comparative technique.

Flame AAS determination of metal ions in fuel ethanol after preconcentration on acid carboxymethylcellulose (CMCH)

This paper describes the preparation of acid carboxymethylcellulose (CMCH), and the results of a study on the adsorption and preconcentration (using batch and flow-through column methods) of Cd(II), Cu(II), Cr(III), Fe(III), Ni(II) and Zn(II) in ethanol medium. The adsorption capacities for each metallic ion were (in mmol g(-1)) Cd(II) = 0.92; Cu(II) = 1.45; Cr(III) = 1.70; Fe(III) = 1.60; Ni(II) = 1.30; and Zn(II) = 1.10. By means of the flow-through method, a recovery of ca. 100% of the metallic ions adsorbed in a column packed with 2 g of CMCH was found when 5.0 mL of 1.0 mol L-1 hydrochloric acid were used as eluent. An enrichment factor of 20 (100 mt solution containing 50 mu g L-1 of the metallic ions, concentrated to 5.0 mt) was obtained by this preconcentration procedure. The sorption-desorption procedure applied allowed the development of a preconcentration and Flame AAS quantification method of metallic ions in fuel ethanol at trace levels.

Determination of Cu, Ni, and Zn in fuel ethanol by FAAS after enrichment in column packed with 2-aminothiazole-modified silica gel

This work describes the synthesis and characterization of 2-aminothiazole-modified silica gel (SiAT), as well as its application for preconcentration (in batch and column technique) of Cu(II), Ni(II) and Zn(II) in ethanol medium. The adsorption capacities of SiAT determined for each metal ion were (mmol g(-1)): Cu(II)=1.20, Ni(II)=1.10 and Zn(II)=0.90. In addition, results obtained in flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 500 mg of SiAT. The eluent was 2.0 mol L-1 HCl. The sorption-desorption of the studied metal ions made possible the development of a preconcentration method for metal ions at trace level in fuel ethanol using flame AAS for their quantification.

Analytical Methods Employed at Quality Control of Fuel Ethanol

The existence of organic and inorganic contaminants present in both fossil and biomass fuels and the fact that they can provide undesirable effects (environmental problems, corrosion processes, lead to storage instability, and others) implies a rigorous quality control of these fuels, although these contaminants make up a small part of the final fuel composition. Considering the rising importance of fuel ethanol in the worldwide panorama, this review aims at reporting the use of successful alternative analytical methods in the monitoring of organic and inorganic contaminants at trace levels, used to determine and to quantify these substances in fuel ethanol and also presenting all official norms for quality control of fuel ethanol employed by ABNT (Brazilian Association of Technical Norms), ASTM (American Society for Testing and Materials), and ECS (European Committee for Standardization).

Simultaneous determination of Cu and Pb in fuel ethanol by graphite furnace AAS using tungsten permanent modifier with co-injection of Ir

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by GFAAS

A method has been developed for the simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by graphite furnace atomic absorption spectrometry (GFAAS) using a transversely heated graphite atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of analytes during the pyrolysis and atomization stages using the mixture Pd(NO3)(2) + Mg(NO3)(2) as the chemical modifier was investigated in 0.028 mol L-1 HNO3, 0.14 mol L-1 HNO3, and diluted ethanol (1 + 1, v/v) containing different nitric acid concentrations. With 5 rhog Pd + 3 mug Mg as the modifiers, pyrolysis and atomization temperatures of the heating program of the atomizer were fixed at 1200 C and 2200degreesC respectively. For 20 muL of diluted sample (10 muL ethanol + 10 muL of 0.28 mol L-1 HNO3) dispensed into the graphite tube, analytical curves in the 2.0 - 50 mug L-1 Al, As, Cu, Fe, Mn, Ni ranges were established. The calculated characteristic masses were - 37 pg Al, 73 pg As, 31 pg Cu, 16 pg Fe, 9 pg Mn, and 44 pg Ni, and the lifetime of the tube was around 2 50 firings. The limits of detection (LOD) based on integrated absorbance were 1.2 mug L-1 Al, 2.5 mug L-1 As. 0.22 mug L-1 Cu, 1.6 L-1 Fe 0.20 mug L-1 Mn 1.1 mug L-1 Ni. The relatively standard deviations (n = 12) were less than or equal to 3%, less than or equal to 6%, less than or equal to 2%, less than or equal to 3.4%, less than or equal to 1.3%, and less than or equal to 2% for Al, As, Cu, Fe, Mn, and Ni, respectively, the recoveries of Al, As, Cu, Fe, Mn and Ni added to fuel ethanol samples varied from 77% to 112%, 92% to 114%, 104% to 113%, 73% to 116%, 91% to 122% and 93% to 116%, respectively. Accuracy was checked for Al, As, Cu, Fe, Mn, and Ni determination in 20 samples purchased at local gas stations in Araraquara city, Brazil. A paired t-test showed that the results were in agreement at the 95% confidence level with those obtained by single-element GFAAS.

CURRENT ASPECTS OF FUEL ETHANOL-PRODUCTION IN BRAZIL

Brazil has become a great producer of bioethanol using sugarcane as the basic raw material. Fed-batch process and continuous process are used. Biogas generation from vinasse, production of dry yeast, and autolyzed bagasse for animal feed are making the ethanol production less polluting and more profitable. Bagasse surplus has also been converted into electrical energy. Another alternative use for bioethanol is its conversion to petrochemical derivatives. Up to the present, however, this conversion has been carried out on only a small scale by the industry.

Direct determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by simultaneous GFAAS using integrated platforms pretreated with W-Rh permanent modifier together with Pd plus Mg modifier

A method is proposed for the simultaneous determination of Al, As, Cu, Fe, Mn, and Ni in fuel ethanol by electrothermal atomic absorption spectrometry (ETAAS) using W-Rh permanent modifier together with Pd(NO3)(2) + Mg(NO3)(2) conventional modifier. The integrated platform of a transversely heated graphite atomizer (THGA) was treated with tungsten, followed by rhodium, forming a deposit containing 250 mug W + 200 mug Rh. A 500-muL, volume of fuel ethanol was diluted with 500 muL, of 0.14 mol L-1 HNO3 in an autosampler cup of the spectrometer. Then, 20 muL, of the diluted ethanol was introduced into the pretreated graphite platform followed by the introduction of 5 mug Pd(NO3)(2) + 3 mug Mg(NO3)(2). The injection of this modifier was required to improve arsenic and iron recoveries in fuel ethanol. Calibrations were carried out using multi-element reference solutions prepared in diluted ethanol (1 + 1, v/v) acidified to 0. 14 mol L-1 HNO3. The pyrolysis and atomization temperatures of the heating program were 1200degreesC and 2200degreesC, respectively, which were obtained with multielement reference solutions in acidic diluted ethanol (1 + 1, v/v; 0. 14 mol L-1 HNO3). The characteristic masses for the simultaneous determination in ethanol fuel were 78 pg Al, 33 pg As, 10 pg Cu, 14 pg Fe, 7 pg Mn, and 24 pg Ni. The lifetime of the pretreated tube was about 700 firings. The detection limits (D.L.) were 1.9 mug L-1 Al, 2.9 mug L-1 As, 0.57 mug L-1.Cu, 1.3 mug L-1 Fe, 0.40 mug L-1 Mn, and 1.3 mug L-1 Ni. The relative standard deviations (n = 12) were 4%, 4%, 3%, 1.5%, 1.2%, and 2.2% for Al, As, Cu, Fe, Mn, and Ni, respectively. The recoveries of Al, As, Cu, Fe, Mn, and Ni added to the fuel ethanol samples varied from 81% to 95%, 80% to 98%, 97% to 109%, 85% to 107%, 98% to 106% and 97% to 103%, respectively. Accuracy was checked for the Al, As, Cu, Fe, Mn, and Ni determination in 10 samples purchased at a local gas station in Araraquara-SP City, Brazil. A paired t-test showed that at the 95% confidence level the results were in agreement with those obtained by single-element ETAAS.

Determination of nickel in fuel ethanol using a carbon paste modified electrode containing dimethylglyoxime

A mercury-free electrode chemically modified with carbon paste containing dimethylglyoxime was used for determination of nickel in fuel ethanol. The instrumental parameters and composition of the modified paste were optimized. The analytical curve for nickel determination from 5.0 x 10(-9) to 5.0 x10(-7) mol(-1) was obtained using 25 min of accumulation time. The detection limit and amperometric sensitivity obtained for this method were 2.7 x 10 mol(-1) and 5.2 x 10(8) mu A mol(-1) L, respectively. The values for nickel concentration in four commercial samples of fuel ethanol were obtained in the range of 1.1 x 10(-8) to 6.9 x 10(-8) mol(-1). A comparison to graphite furnace atomic absorption spectrometry (GFAAS) was performed for nickel determination in commercial samples of ethanol.

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). Welldefined 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 -0.90V, 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 x 10(-6)-1.00 x 10(-4) M of acetaldehyde. The detection limit is 8.14 x 10(-7) M. The method has been applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pretreatment.

Determination of metal ions in fuel ethanol after preconcentration on 5-amino-1,3,4-thiadiazole-2-thiol modified silica gel

This work describes the synthesis and characterization of 5-amino-1,3,4-thiadiazole-2-thiol modified silica gel (SiATT), and the results of a study of the adsorption and preconcentration (in batch, and in flow using a column technique) of Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II) and Zn(II) in ethanol medium. The adsorption capacities for each metal ion were (in mmol g -1): Cd(II) = 0.11, Co(II) = 0.10, Cu(II) = 0.20, Fe(III) = 0.20, Ni(II) = 0.16, Pb(II) = 0.08 and Zn(II) = 0.12. The results obtained in the flow experiments, showed a recovery of ca. 100% of the metal ions adsorbed in a column packed with 2 g of SiATT, using 5 mL of 2.0 mol L -1 HCl solution as eluent. The sorption-desorption of the metal ions made possible the development of a preconcentration method and quantification by Flame AAS of metal ions at trace level in fuel ethanol.

New methodology for pH measurements in fuel ethanol using glass electrode

Studies carried out with glass electrode in anhydrous ethanol and ethanol-water solutions for measuring pH values have shown that this parameter depends on the solution composition, the contact time with the solution, the utilized temperature, and the type of electrolyte used. It was also observed that the glass electrode behavior in an acid medium differs from an alkaline medium. These studies provided correction factors for pH values from 2 to 12, allowing the realization of proper measurements of the hydrogen ionic activity in the ethanol-water and anhydrous ethanol solutions. However, these correction factors could not be applied to the fuel ethanol. Alternatively, a new method was developed for the correction of the pH values, which can be applied in hydrous and anhydrous fuel ethanol samples. Copyright © 2011 by ASTM International.