Simultaneous determination of Cu, Pb, Cd, Ni, Co and Zn in bioethanol fuel by adsorptive stripping voltammetry and multivariate linear regression (original) (raw)
Microchemical Journal, 2013
In the present work, the simultaneous optimization of multiple responses was applied to the optimization of the simultaneous determination of trace levels of Cd(II), Cu(II), Pb(II) and Zn(II) via anodic stripping voltammetry (ASV) at a bismuth film electrode. Two different approaches were evaluated: i) use of individual responses such as peak current and its coefficient of variation; and ii) use of the full-voltammogram by means of a recent chemometrics method named analysis of variance-principal component analysis (ANOVA-PCA). Deposition time and voltage step were the most important factors identified with both optimization procedures. The optimized method was applied to the determination of trace levels of Cd(II), Cu(II), Pb(II) and Zn(II) in biodiesel samples after microwave digestion with diluted acid, presenting satisfactory values for accuracy and precision. For 0.1 g of digested biodiesel sample, the values found for the limits of quantification were 0.23 μg g −1 for Cd, 0.09 μg g −1 for Cu, 0.39 μg g −1 for Pb, and 3.5 μg g −1 for Zn.
Analytical and …, 2004
A new, versatile, and simple method for quantitative analysis of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry is described. These metals can be quantified by direct dissolution of fuel ethanol in water and subsequent voltammetric measurement after the accumulation step. A maximum limit of 20% (v/v) ethanol in water solution was obtained for voltammetric measurements without loss of sensitivity for metal species. Chemical and operational optimum conditions were analyzed in this study; the values obtained were pH 2.9, a 4.7-lm thickness mercury film, a 1,000-rpm rotation frequency of the working electrode, and a 600-s pre-concentration time. Voltammetric measurements were obtained using linear scan (LSV), differential pulse (DPV), and square wave (SWV) modes and detection limits were in the range 10 À9 -10 À8 mol L À1 for these metal species. The proposed method was compared with a traditional analytical technique, flame atomic absorption spectrometry (FAAS), for quantification of these metal species in commercial fuel ethanol samples.
Resolution of Voltammetric Peaks Using Chemometric Multivariate Calibration Methods
Electroanalysis, 2001
The capacity of chemometric multivariate calibration methods, partial least square (PLS) and principal component regression (PCR), to extract quantitative analytical information from overlapping peaks in anodic stripping voltammetry is illustrated in the simultaneous analysis of synthetic mixtures containing Pb(II), In(III), Cd(II), and Tl(I). The influence of raw and first derivative data in the predictive ability of the calibration models was discussed and the results obtained in the analytical performance of synthetic mixtures by PLS and PCR were compared. The analytical results show no observable differences between the two methods and the utilization of derivative data did not improve the prediction step.
Journal of the Brazilian Chemical Society, 2018
A novel and simple electroanalytical method for the determination of Cu 2+ in biodiesel samples by stripping voltammetric analysis was developed. The method employs a carbon paste electrode (CPE) modified with Vulcan carbon, previouly functionalized with carbazone (CBZ). The CPE/Vulcan-CBZ sensor promoted a significant increase in the analytical signal obtained from copper as compared to unmodified CPE, and the CPE modified with Vulcan carbon (CPE/ Vulcan). Vulcan-CBZ, Vulcan and CBZ materials were characterized by Fourier transform infrared spectroscopy (FTIR) technique. The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and square-wave anodic stripping voltammetric (SWASV) techniques. The CPE/Vulcan-CBZ modified electrode showed excellent response and was able to detect Cu 2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu 2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L-1 ammonium sulfate solution ((NH 4) 2 SO 4), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu 2+ concentrations in the range from 6 to 190 nmol L-1 (r = 0.998), with a detection limit of 1.2 nmol L-1. The sensor was successfully applied for the determination of Cu 2+ in biodiesel and the average recovery varied between 97.0 and 102.8% for the soybean biodiesel samples and between 109.6 and 111.0% for the babassu biodiesel samples showing a good accuracy for the proposed method.
Analytica Chimica Acta, 2006
A new method was developed for simultaneous determination of copper, lead, and cadmium, based on their voltammetric response at a carbon paste electrode modified with hexagonal mesoporous silica (HMS) immobilized quercetin (HMS-Qu/CPE). Compared with quercetin modified carbon paste electrode (Qu/CPE) and quercetin ionic liquid modified carbon paste electrode (Qu-IL/CPE), the HMS-Qu/CPE exhibited improved selectivity and high sensitivity toward the detection of copper, lead, and cadmium. The properties of the HMS-Qu/CPE in 0.1 M HCOONa-HCl buffer solution (pH4.7) were investigated by adsorptive stripping voltammetry (ASV) and electrochemical impedance spectroscopy (EIS). The electrochemical behavior of copper, lead, and cadmium at the modified electrodes and factors affecting the preconcentration procedures were also investigated. Detection limits of 5.0, 0.8, 1.0 nM for copper, lead, and cadmium were obtained, respectively. The method is simple, fast, sensitive, and selective, and is successfully applied to soil sample.
Analytica Chimica Acta, 2004
A procedure for the determination o f nickel by adsorptive stripping voltammetry (AdSV), using dimethylglyoxime as complexing agent, has been optimized. The determination was carried out by two different techniques: differential pulse adsorptive stripping voltammetry (DPAdSV) and square wave adsorptive stripping voltammetry (SWAdSV). The selection of the experimental parameters was done using a factorial design which allows one to find the most significant variables, i.e., those which exert the greatest influence on the measured magnitude, with a reduced number of experiments. Posterior optimization of these variables provided the most adequate experimental conditions and it was under these conditions that the calibrations were made, using a robust regression method which allows the elimination of anomalous points.
Central European Journal of Chemistry, 2009
A partial least squares (PLS-1) calibration model based on kinetic--spectrophotometric measurement, for the simultaneous determination of Cu(II), Ni(II) and Co(II) ions is described. The method was based on the difference in the rate of the reaction between Co(II), Ni(II) and Cu(II) ions with 1-(2-pyridylazo)2-naphthol in a pH 5.8 buffer solution and in micellar media at 25 o C. The absorption kinetic profiles of the solutions were monitored by measuring the absorbance at 570 nm at 2 s intervals during the time range of 0 -10 min after initiation of the reaction. The experimental calibration matrix for the partial least squares (PLS-1) model was designed with 30 samples. The cross-validation method was used for selecting the number of factors. The results showed that simultaneous determination could be performed in the range 0.1-2 µg mL -1 for each cation. The proposed method was successfully applied to the simultaneous determination of Cu(II), Ni(II) and Co(II) ions in water and in synthetic alloy samples.
Multivariate linear regression aided by a successive projections algorithm (SPA-MLR) was applied in the evaluation of anodic stripping voltammetry data obtained in the simultaneous determination of metals under conditions where there were significant complications due to interference processes such as the formation of intermetallic compounds and overlapping peaks. Using simulated data, modeled from complex interactions experimentally observed in samples containing Cu and Zn, as well as Co and Zn, it was demonstrated that SPA-MLR selected variables that allow chemical interpretation. This feature was used to make inferences about the underlying electrochemical processes during the simultaneous determination of four metals (Cu, Pb, Cd, and Co) in a concentration range where all responses were complicated by interference processes (10-100 ng mL −1 ). Additionally, the analytical performances of MLR models for quantitative predictions were excellent despite the complexity of the system under study.
Fuel, 2012
In this paper a rapid method of anodic stripping voltammetry (ASV) coupled with experimental design was developed for simultaneous determination of Zn 2+ , Cd 2+ , Pb 2+ , and Cu 2+ in gasoline samples. A microwave assisted gasoline digestion procedure for sample preparation was also established. The determination limit was found to be 0.24 lg L À1 for Zn 2+ ; 8.58 Â 10 À4 lg L À1 for Cd 2+ ; 0.13 lg L À1 for Pb 2+ , and 0.87 lg L À1 for Cu 2+. It was found that the interferences of concomitant metal ions were negligible. Gasoline samples collected in the city of São Luis (MA), Brazil were analyzed using this developed method, and the results demonstrated that this method was reliable and accurate. It is expected that this method can be used as a routine technique for metal ion determination in gasoline.
Direct Determination of Copper in Biodiesel Using Stripping Analysis
A simple, effective, and low-cost protocol for copper determination in biodiesel, with no sample decomposition, is reported. Samples were diluted in an ethanol-water solution (with HCl as supporting electrolyte) generating a homogeneous mixture at which copper was directly detected using stripping chronopotentiometry using a gold working-electrode. The optimized mixture was 100 mL (0.088 g) of biodiesel, 15 mL of ethanol, and 5 mL of 0.1 mol L À1 HCl aqueous solution. The estimated detection limit was 200 ng g À1 (300-s deposition time). The elimination of the sample treatment step offers the possibility of on-site measurements in association with commercially-available portable potentiostats.
Analytica Chimica Acta, 1994
The application of adsorptive cathodic stripping voltammetry (ACSV) for the determination of Cu, Cd, Ni and Co in acid digested atmospheric samples was carried out. The accuracy of the technique was evaluated and compared with GFAAS (graphite furnace atomic absorption spectrometry) and ICP-MS (inductively coupled plasma mass spectrometry) using a standard reference material (MESS-l). All the considered techniques had the required accuracy. Detection limits were lowest for Cu and Ni using ACSV (0.30 and 0.08 ng ml-' for a 10 x diluted sample and a 1 min collection, respectively) whereas for Co detection limits were lowest by direct determination using ICP-MS analysis (0.03 ng ml-'). GFAAS had the lowest limit of detection for Cd (0.3 ng ml-'). Cd was not determined by ICP-MS in both MESS-l and aerosol digests due to a higher detection limit. For all considered metals determined in low volume aerosol there were no statistical differences between all three techniques. In addition, there was no observable difference in the metal concentrations in the reference material during ACSV analysis of samples before and after UV irradiation. However a significant difference was observed between ACSV analysis before and after UV irradiation for Cu and Cd in aerosol acid digest samples but no such difference was detected for Ni. This would indicate significant dissolved organic component interference by competitive complexation of Cu and Cd in the aerosol digest samples.
MCR-ALS of voltammetric data for the study of environmentally relevant substances
Microchemical Journal, 2020
A critical revision is made on the main approaches and results arising from the combination of multivariate curve resolution by alternating least squares (MCR-ALS) and electroanalytical measurements in the field of environmental analytical chemistry. Although most of the work done has been focused on the study of the metal binding properties of metal bioregulators such as metallothioneins or phytochelatins, new perspectives appear in the evolving world of sensors for environmental monitoring.
Talanta, 2007
Solid paraffin-based carbon paste electrodes modified with 2-aminothiazole organofunctionalized silica have been applied to the anodic stripping determination of copper ions in ethanol fuel samples without any sample treatment. The proposed method comprised four steps: (1) copper ions preconcentration at open circuit potential directly in the ethanol fuel sample; (2) exchange of the solution and immediate cathodic reduction of the absorbate at controlled potential; (3) differential pulse anodic stripping voltammetry; (4) electrochemical surface regeneration by applying a positive potential in acid media. Factors affecting the preconcentration, reduction and stripping steps were investigated and the optimum conditions were employed to develop the analytical procedure. Using a preconcentration time of 20 min and reduction time of 120 s at −0.3 V versus Ag/AgCl sat a linear range from 7.5 × 10 −8 to 2.5 × 10 −6 mol L −1 with detection limit of 3.1 × 10 −8 mol L −1 was obtained. Interference studies have shown a decrease in the interference effect according to the sequence: Ni > Zn > Cd > Pb > Fe. However, the interference effects of these ions have not forbidden the application of the proposed method. Recovery values between 98.8 and 102.3% were obtained for synthetic samples spiked with known amounts of Cu 2+ and interfering metallic ions. The developed electrode was successfully applied to the determination of Cu 2+ in commercial ethanol fuel samples. The results were compared to those obtained by flame atomic absorption spectroscopy by using the F-test and t-test. Neither F-value nor t-value have exceeded the critical values at 95% confidence level, confirming that there are no significant differences between the results obtained by both methods.
… and Technology of …, 2008
After several petroleum crises in the 70's and 80's successive increases in petroleum barrel prices stimulated worldwide research and development of alternative fuels relative to fossil fuels. In this context, fuel ethanol obtained from sugarcane has been successfully applied as an important automotive fuel used in large scale in Brazil, in the pure form or as an addictive for gasoline, thus contributing economic and environmental advantages.
A simple, novel and sensitive spectrophotometric method was described for the simultaneous determination of cobalt, nickel and palladium. The method is based on the complex formation of Co, Ni and Pd with 1-(2-pyridylazo)-2-naphtol (PAN) in Tween-80 micellar media. All factors affecting on the sensitivity were optimized and the linear dynamic range for determination of Co, Ni and Pd was found. The experimental calibration matrix was designed by measuring the absorbance over the range of 520-700 nm for 21 samples of 0.10-1.0, 0.050-0.50 and 0.050-4.0 g ml −1 of Co, Ni and Pd, respectively. The partial least square (PLS) modeling based on singular value decomposition (SVD) was used for the multivariate calibration of the spectrophotometric data. The direct orthogonal signal correction was used for pre-processing of data matrices and the prediction results of model, with and without using direct orthogonal signal correction, were statistically compared. The effects of various anions and cations on selectivity of the method were investigated. The proposed method was successfully applied to the determination of Co, Ni and Pd in water and alloy samples.
1998
Accurate qualitative and quantitative results were obtained by the application of parameter estimation methods, viz. Classical Least Squares 'CLS', Inverse Least Squares 'ILS' and Kalman Filter 'KF' algorithms. These methods were used to separate strongly overlapping electrochemical peaks produced by binary, ternary and quaternary mixtures of traces of cited poisonous heavy metals stripped from the hanging mercury drop electrode in an acetate-bromide electrolyte using the square wave anodic stripping voltammetry. The analysis was achieved using a single standard addition, the concentrations studied were down to 50 nM and molar ratios up to 1:6 for binary mixtures. A statistical analysis of the results was reported. The method was applied for the ultratrace analysis of the cited cations in a sample of sodium hydrogen carbonate AR.
Energy & Fuels, 2019
25 A methodology for direct and simultaneous determination of four phenolics 26 antioxidants-butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), 27 propyl gallate (PG), and tert-butylhydroquinone (TBHQ)-in biodiesel samples using 28 differential pulse voltammetry (DPV) associated with partial least squares (PLS) 29 regression is presented. Measurements were taken directly in biodiesel:ethanol 1:1 30 (v/v) medium using a platinum ultramicroelectrode (ume) as working electrode. The 31 voltammetric signals of the compounds overlapped significantly, and to facilitate the 32 simultaneous determination of the analytes, a PLS chemometric tool was applied 33 and approaches fitting one compound at a time (PLS-1) and multiple compounds 34 (PLS-2) both allowed the quantification of the individual concentrations, overcoming 35 the strongly overlapped voltammograms. Results show that the PLS-2 model 36 provides more accurate predictions than PLS-1. For the PLS-2 model, root mean 37 square errors of prediction (RMSEP) of 3x10 1 , 16, 24 and 3x10 1 mg L-1 have been