Alternative method for rhamnolipids quantification using an electrochemical platform based on reduced graphene oxide, manganese nanoparticles and molecularly imprinted Poly(L-Ser).

Rhamnolipids (RHLs) are promising biosurfactants with important applications in several industrial segments. These compounds are produced through biotechnological processes using the bacteria Pseudomonas Aeruginosa. The main methods of analyzing this compound are based on chromatographic techniques. In this study, an electrochemical sensor based on a platform modified with reduced graphene oxide, manganese nanoparticles covered with a molecularly imprinted poly (L-Ser) film was used as an alternative method to quantify RHL through its hydrolysis product, acid 3-hydroxydecanoic acid (3-HDA). The proposed sensor was characterized microscopically, spectroscopically and electrochemically. Under optimized experimental conditions, an analytical curve was obtained in the linear concentration range from 2.0 × 10-12 mol L-1 to 1.0 × 10-10 mol L-1. The values estimated of LOD, LOQ and AS were 8.3 × 10-13 mol L-1, 2.7 × 10-12 mol L-1and 1.3 × 107 A L mol-1, respectively. GCE/rGO/MnNPs/L-Ser@MIP exhibits excellent selectivity, repeatability, and high stability for the detection of 3-HDA. Furthermore, the developed method was successfully applied to the recognition of the hydrolysis product (3-HDA) of RHLs obtained from guava agro-waste. Statistical comparison between GCE/rGO/MnNPs/L-Ser@MIP and HPLC method confirms the accuracy of the electrochemical sensor within a 95% confidence interval.

Electrochemical sensor based on carbon nanotube decorated with manganese oxide nanoparticles for naphthalene determination.

In this work, an electrochemical sensor was developed for the determination of naphthalene (NaP) in well water samples, based on a glass carbon electrode (GCE) modified as a nanocomposite of manganese oxides (MnOx) and COOH-functionalized multi-walled carbon nanotubes (MWCNT). The synthesis of MnOx nanoparticles was performed by the sol-gel method. The nanocomposite was obtained by mixing MnOx and MWCNT with the aid of ultrasound, followed by stirring for 24 h. Surface modification facilitated the electron transfer process through the MnOx/MWCNT/GCE composite, which was used as an electrochemical sensor. The sensor and its material were characterized by cyclic voltammetry (CV), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Important parameters influencing electrochemical sensor performance (pH, composite ratios) were investigated and optimized. The MnOx/MWCNT/GCE sensor showed a wide linear range of 2.0-16.0 µM, a detection limit of 0.5 µM and a quantification limit of 1.8 µM, in addition to satisfactory repeatability (RSD of 7.8%) and stability (900 s) in the determination of NaP. The determination of NaP in a sample of water from a gas station well using the proposed sensor showed results with recovery between 98.1 and 103.3%. The results obtained suggest that the MnOx/MWCNT/GCE electrode has great potential for application in the detection of NaP in well water.

Using a disposable platform based on reduced graphene oxide, iron nanoparticles and molecularly imprinted polymer for voltammetric determination of vanillic acid in fruit peels.

This work reports the development and application of a disposable electrochemical platform for vanillic acid (VA) detection using screen-printed electrode modified with reduced graphene oxide, iron nanoparticles and molecularly imprinted poly(pyrrole) film. The electrochemical platform was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Using optimized conditions, the proposed disposable platform presented linear concentration ranges of 1.0 × 10-9 to 1.5 × 10-7 mol/L. The limits of detection and quantification obtained for the device were 3.1 × 10-10 and 1.0 × 10-9 mol/L, respectively. The electrochemical platform was found to be selective for VA recognition and presented voltammetric responses with good repeatability and stability. The analytical methodology developed was applied for VA determination in banana and orange peels. The results obtained showed that the proposed electrochemical platform has a good accuracy when applied for the determination of VA.

Sample preparation and antibiotic quantification in vinasse generated from sugarcane ethanol fuel production.

Vinasse - liquid organic residue derived from the production of sugarcane ethanol fuel, has been applied as soil amendment via fertigation for decades in Brazil. This organic residue is an important source of nutrients and water for sugarcane crops. Through fertigation, approximately 400 billion liters of vinasse are recycled annually. Despite the economic and agronomic importance of this practice, vinasse-based fertigation can be a source of antibiotic contamination in the environment. The present work reports the application of solid phase extraction (SPE), salting-out liquid-liquid extraction (SALLE), and on-line solid phase extraction (on-line SPE) as sample preparation techniques for the analysis of the following antibiotics (contaminants) in vinasse sample: monensin, penicillin G, virginiamycin M1, virginiamycin S1, tetracycline and erythromycin. The study also employed a totally automated quantitative method based on on-line SPE and liquid chromatography coupled to quadrupole linear ion trap tandem mass spectrometry (LC-QqLIT-MS/MS) for the analysis of these contaminants in vinasse. The application of the aforementioned sample preparation techniques led to the successful extraction of the analytes, and a comparative analysis of the techniques showed that the on-line SPE technique was the most advantageous among the techniques investigated. The quantitative analytical method applied yielded well-defined chromatographic peaks, working range of 1.0-370.0 ng·mL-1, apparent recovery ranging from 80 to 110% for most compounds, repeatability between 3 and 16%, and limits of detection ranging from1.0 to 10 ng·mL-1. The analysis of six vinasse samples from different ethanol producing plants led to the detection of monensin at the concentration of 14.3 ng·mL-1 in their compositions. The results obtained show that fertigation with vinasse is a source of antibiotic contamination in the environment.

Underivatized amino acids detection by anion-exchange chromatography coupled to a nanostructured detector.

This work reports the development of a fast and reliable amperometric sensor for the detection of amino acids. The detector was constructed using copper nanoparticles (CuNPs) supported on reduced graphene oxide (RGO) modified glassy carbon electrode (CuNPs-RGO/GCE) and based on the application of high performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Under optimized isocratic HPAEC-PAD conditions (using 40 mmol L-1 NaOH as mobile phase, flow rate of 0.30 mL min-1 and detection potential of 0.45 V vs. Pd/PdO), the linear dynamic ranges of the concentration of amino acids obtained were 0.50-50 µmol L-1 for lysine, 1.0-100 µmol L-1 for alanine, glycine and serine, and 5.0-100 µmol L-1 for leucine. The limits of detection (S/N = 3) obtained ranged from 0.10 (for lysine and leucine) to 0.50 µmol L-1 (for alanine, glycine and serine) and sensitivity varied from 6.1 (for leucine) to 21.5 nA µmol-1 L (for serine). The average recovery percentages ranged from 97% (for glycine) to 102% (for leucine and serine). The results obtained showed that the CuNPs-RGO/GCE has good long-term stability, repeatability and reproducibility; this makes the device suitable for application as an electrochemical detector. The successful application of the proposed method for the analysis of sugarcane vinasse demonstrates its suitability for separation and determination of amino acids in complex matrices.

Fructose determination in fruit juices using an electrosynthesized molecularly imprinted polymer on reduced graphene oxide modified electrode.

The present work reports the development of a novel electrochemical sensor for the selective detection of fructose. The sensor was developed through electropolymerization of a molecularly imprinted polymer film on a reduced graphene oxide modified electrode. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, atomic force microscopy and RAMAN spectroscopy. Through the application of the modified electrode, the recognition of fructose molecules occurred in a concentration range of 1.0 × 10-14 to 1.0 × 10-11 mol L-1, under a Langmuir adsorption isothermal model. The sensitivity and limits of detection and quantification obtained for the sensor were 9.9 × 107 A L mol-1, 3.2 × 10-15 mol L-1 and 1.1 × 10-14 mol L-1, respectively. The analytical method used for the detection of fructose presented good reproducibility, stability and accuracy, and was successfully applied for the quantification of this sugar in orange, apple and grape juices.

Electrosynthesis of three-dimensional nanoporous nickel on screen-printed electrode used for the determination of narirutin in citrus wastewater.

In this study, an electrochemical sensor was designed for the detection of narirutin using three-dimensional nanostructured porous nickel on screen-printed electrode (3DnpNi/SPE). The modified electrode was successfully synthesized by the dynamic hydrogen bubble template method. The 3DnpNi/SPE was characterized by spectroscopic, microscopic, and electrochemical methods. The results showed that the 3DnpNi/SPE presents good electrocatalytic activity for the oxidation of narirutin. The quantification of narirutin was conducted by differential pulse voltammetry, which showed a wide concentration range (1.0 × 10-7 - 1.0 × 10-5 mol L-1), with low detection limit (3.9 × 10-8 mol L-1), and excellent sensitivity (0.31 A L mol-1). The proposed electrode was applied toward the determination of narirutin in yellow water sample from the citrus industry, where it presented a good degree of accuracy. The 3DnpNi/SPE showed repeatability, long-term stability, and selectivity. The results obtained showed agreement with those obtained by HPLC/DAD method. Chemical compounds studied in this article.

Non-enzymatic lactose molecularly imprinted sensor based on disposable graphite paper electrode.

Lactose (LAC) is a disaccharide - major sugar, present in milk and dairy products. LAC content is an important indicator of milk quality and abnormalities in food industries, as well as in human and animal health. The present study reports the development of an innovative imprinted voltammetric sensor for sensitive detection of LAC. The sensor was constructed using electropolymerized pyrrole (Py) molecularly imprinted polymer (MIP) on graphite paper electrode (PE). The MIP film was constructed through the electrosynthesis of polypyrrole (PPy) in the presence of LAC (template molecule) on PE (PPy/PE). To optimize the detection conditions, several factors affecting the PPy/PE sensor performance were assessed by multivariate methods (Plackett-Burman design and central composite design). Under optimized conditions, the proposed analytical method was applied for LAC detection in whole and LAC-free milks, where it demonstrated high sensitivity and selectivity, with two dynamic linear ranges of concentration (1.0-10 nmol L-1 and 25-125 nmol L-1) and a detection limit of 0.88 nmol L-1. The MIP sensor showed selective molecular recognition for LAC in the presence of structurally related molecules. The proposed PPy/PE sensor exhibited good stability, as well as excellent reproducibility and repeatability. Based on the results obtained, the PPy/PE is found to be highly promising for sensitive detection of LAC.

Identification of organic contaminants in vinasse and in soil and groundwater from fertigated sugarcane crop areas using target and suspect screening strategies.

This work evaluated for the first time the sustainability of vinasse reuse as a fertilizer in sugarcane crops by assessing the occurrence of organic contaminants and their potential for dissemination to soils and groundwater in fertigated areas. A comprehensive screening of organic contaminants was performed in vinasse, soil and groundwater using target analysis, to investigate the occurrence of multiple-class antibiotics, in combination with suspect screening using NORMAN Digital Sample Freezing Platform. Even though antibiotics are used in the ethanol production process and were expected to be ubiquitous contaminants, they were not detected in any of the samples. Nevertheless, the HRMS-based wide-scope suspect screening (including >7800 substances such as pharmaceuticals, agrochemicals, preservatives and industrial chemicals) allowed the tentative identification of 56 compounds, mostly pesticides, food additives, industrial and naturally occurring substances. Results showed no overlap between the compounds detected in vinasse and environmental samples, suggesting that the pollutants found in soil and groundwater might come from alternative sources other than vinasse reuse.

Pressurized Liquid Extraction (PLE) and QuEChERS evaluation for the analysis of antibiotics in agricultural soils.

Vinasse, a liquid waste which originates from the production of ethanol fuel from sugarcane, has been widely used as soil amendment in Brazil. An important concern that arises from vinasse reuse is the dissemination of antibiotics to the environment through crop soils. This work evaluated the performance of Pressurized Liquid Extraction (PLE) and QuEChERS (quick, easy, cheap, effective, rugged and safe) to extract several multiple-class antibiotics, such as cephalosporins, fluoroquinolones, ionophores, lincosamides, macrolides, quinolones, streptogramin, sulfonamides, tetracyclines and others, from agricultural soils. The performance of several parameters was evaluated for both PLE and QuEChERS, such as the extraction temperature (for PLE), solvents composition, pH and the addition of EDTA. Both methods were able to extract most target antibiotics. However, QuEChERS showed higher recoveries for macrolides and nitroimidazoles, while PLE was more suitable for fluoroquinolones and ionophores (i.e. monensin). The use of citrate-phosphate buffer at pH 7.0, in combination with methanol for PLE and with acetonitrile for QuEChERS, provided the highest antibiotic recoveries for both methods. The use of EDTA did not increase antibiotic recovery rates for QuEChERS, while the temperature had almost no influence on the extraction efficiency in PLE.•Citrate-phosphate buffer at pH 7.0 provided higher antibiotic recoveries for QuEChERS and PLE.•The combination buffer-methanol provided higher recoveries for PLE.•QuEChERS and PLE methods were able to extract most of the target antibiotics.

Electrochemical sensor based on reduced graphene oxide and molecularly imprinted poly(phenol) for d-xylose determination.

The present work reports the development of an electrochemical sensor based on molecularly imprinted polymer for the determination of d-xylose. This is the first report of its kind in the literature. The sensor was prepared through the modification of a glassy carbon electrode with reduced graphene oxide and molecularly imprinted poly(phenol) film. The use of graphene oxide and molecularly imprinted poly(phenol) film led to remarkable improvements in the sensor sensitivity and selectivity, respectively. The electrode was characterized by several techniques, including cyclic voltammetry, differential pulse voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy, atomic force microscopy and RAMAN spectroscopy. The proposed sensor presented linear responses ranging from 1.0 × 10-13 to 1.0 × 10-11 mol L-1. The amperometric sensitivity, limit of detection, and limit of quantification obtained were 6.7 × 105 A L mol-1; 8.0 × 10-14 mol L-1 and 2.7 × 10-13 mol L-1 (n = 3), respectively. The proposed analytical method was successfully applied in sugarcane bagasse, which is known to contain large amounts of d-xylose and other structurally similar molecules in its composition. The chemical composition of sugarcane bagasse makes this biomass suitable for evaluating the ability of the sensor to specifically detect the target molecule. Mean recoveries obtained in the analysis ranged from 95.4 to 105.0%; this indicates that the proposed method has good accuracy when applied toward the determination of d-xylose.

Electrochemical sensing of lactate by using an electrode modified with molecularly imprinted polymers, reduced graphene oxide and gold nanoparticles.

This paper reports on a sensitive and selective electrochemical sensor for lactic acid. The sensor is based on molecularly imprinted polymers (MIP), obtained on glassy carbon electrode (GCE) modified with reduced graphene oxide and gold nanoparticles. The MIP was obtained by electropolymerization of the o-phenylenediamine (o-PD) on the modified surface of the GCE in the presence of lactic acid. The steps involving the GCE modification and MIP construction were characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy and atomic force microscopy. The results were evaluated using differential pulse voltammetry, using the hexacyanoferrate redox system as an electrochemical probe. Under optimized experimental conditions, the imprinted sensor has a linear response in the 0.1 nM to 1.0 nM lactic acid concentration range, with detection limit of 0.09 nM. The sensor exhibits excellent selectivity in the presence of molecules of similar chemical structure. It was applied for the selective determination of lactic acid in sugarcane vinasse. The recovery values ranged from 97.7 to 104.8%. Graphical abstractSchematic representation for MIP/AuNP/RGO/GCE sensor, obtained by electropolymerization of o-phenylediamine (o-PD) on a surface modified with gold nanoparticles (AuNPs) and reduced graphene oxide (RGO). These materials allowed the construction of a MIP-sensor with good selectivity for lactic acid.

Amperometric determination of myo-inositol by using a glassy carbon electrode modified with molecularly imprinted polypyrrole, reduced graphene oxide and nickel nanoparticles.

This paper reports on the development of an amperometric method for the determination of myo-inositol. The method involves coating of a glassy carbon electrode (GCE) with a molecularly imprinted polymer (MIP) and reduced graphene oxide (RGO) that was modified with nickel nanoparticles (NiNPs). The MIP was prepared by electropolymerization of pyrrole on the surface of the GCE in the presence of myo-inositol molecules. The construction steps of the modified electrode were monitored via cyclic voltammetry, atomic force microscopy, scanning electron microscopy and X-ray Photoelectron Spectroscopy. The results were evaluated using differential pulse voltammetry, in which hexacyanoferrate was used as an electrochemically active probe. Under optimized experimental conditions, the imprint-modified GCE has a linear response in the 1.0 × 10-10 mol L-1 to 1.0 × 10-8 mol L-1 concentration range, with a 7.6 × 10-11 mol L-1 detection limit and an electrochemical sensitivity of 4.5 µA·cm-2 µmol-1. The method showed improved selectivity even in the presence of molecules with similar chemical structure. The GCE modified was successfully applied to the determination of myo-inositol in sugarcane vinasse where it yielded recoveries that ranged from 95 to 102%. Graphical abstract Schematic presentation of molecularly imprinted polymer (MIP) on a glassy carbon electrode (GCE) modified with nickel nanoparticles (NiNP) anchored in reduced graphene oxide (RGO). The resulting MIP/NiNP/RGO-GCE was used for indirect determination of myo-inositol.

D-mannitol sensor based on molecularly imprinted polymer on electrode modified with reduced graphene oxide decorated with gold nanoparticles.

An electrochemical sensor for D-mannitol based on molecularly imprinted polymer on electrode modified with reduced graphene oxide decorated with gold nanoparticles was developed in this present work. The sensor was constructed for the first time via the electropolymerization of o-phenylenediamine (o-PD) over a surface containing reduced graphene oxide (RGO) and gold nanoparticles (AuNP) in the presence of D-mannitol molecules. The surface modification with AuNP/RGO-GCE facilitated the charge transfer processes of [Fe(CN)6]3-/4-, which was used as an electrochemical probe. It also contributed meaningfully towards the increase in the surface/volume ratio, creating more locations for imprinting, and providing greater sensitivity to the sensor. The MIP/AuNP/RGO-GCE sensor was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscope (SEM), atomic force microscope (AFM) and X-ray Photoelectron Spectroscopy (XPS). Important parameters that exert control over the performance of the molecularly imprinted sensor (such as number of cycles, pH, monomer and template concentration and extraction and rebinding conditions) were investigated and optimized. The imprinting factor was 4.9, showing greater response to the D-mannitol molecule compared to the interfering molecules. The limit of detection, limit of quantification and amperometric sensitivity were 7.7×10-13molL-1, 2.6×10-12molL-1 and 3.9×1010µALmol-1 (n=3) respectively. The MIP/AuNP/RGO-GCE sensor was successfully applied towards the selective determination of D-mannitol in sugarcane vinasse, thus making it, in essence, a valuable tool for the accurate and reliable determination of this molecule.

Determination of furanic aldehydes in sugarcane bagasse by high-performance liquid chromatography with pulsed amperometric detection using a modified electrode with nickel nanoparticles.

A glassy carbon electrode chemically modified with nickel nanoparticles coupled with reversed-phase chromatography with pulsed amperometric detection was used for the quantitative analysis of furanic aldehydes in a real sample of sugarcane bagasse hydrolysate. Chromatographic separation was carried out in isocratic conditions (acetonitrile/water, 1:9) with a flow rate of 1.0 mL/min, a detection potential of -50 mV vs. Pd, and the process was completed within 4 min. The analytical curves presented limits of detection of 4.0 × 10-7 mol/L and 4.3 × 10-7 mol/L, limits of quantification of 1.3 × 10-6 and 1.4 × 10-6 mol/L, amperometric sensitivities of 2.2 × 106 nA mol/L and 2.7 × 106 nA mol/L for furfural and 5-hydroxymethylfurfural, respectively. The values obtained in this sample by the standard addition method were 1.54 ± 0.02 g/kg for 5-hydroxymethylfurfural and 11.5 ± 0.2 g/kg for furfural. The results demonstrate that this new proposed method can be used for the quick detection of furanic aldehydes without the interference of other electroactive species, besides having other remarkable merits that include excellent peak resolution, analytical repeatability, sensitivity, and accuracy.

A simple and fast method for the production and characterization of methylic and ethylic biodiesels from tucum oil via an alkaline route.

A simple, fast, and complete route for the production of methylic and ethylic biodiesel from tucum oil is described. Aliquots of the oil obtained directly from pressed tucum (pulp and almonds) were treated with potassium methoxide or ethoxide at 40°C for 40 min. The biodiesel form was removed from the reactor and washed with 0.1 M HCl aqueous solution. A simple distillation at 100°C was carried out in order to remove water and alcohol species from the biodiesel. The oxidative stability index was obtained for the tucum oil as well as the methylic and ethylic biodiesel at 6.13, 2.90, and 2.80 h, for storage times higher than 8 days. Quality control of the original oil and of the methylic and ethylic biodiesels, such as the amount of glycerin produced during the transesterification process, was accomplished by the TLC, GC-MS, and FT-IR techniques. The results obtained in this study indicate a potential biofuel production by simple treatment of tucum, an important Amazonian fruit.

Effect of a nanostructured dendrimer-naloxonazine complex on endogenous opioid peptides µ1 receptor-mediated post-ictal antinociception.

The aim of this study was to investigate the capacity of the host dendrimer DAB-Am-16 as a drug carrier to reduce the time required for the encapsulated naloxonaxine to establish an irreversible covalent bond with µ(1)-opioid receptor (resulting in a pharmacologically selective effect). The efficacy of dendrimer-naloxonazine nanocomplex (DNC) was studied in antinociception induced by convulsions elicited by intraperitoneal (IP) administration of pentylenetetrazole, and analgesia was measured by the tail-flick test. We found that animals showed increased tail-flick latencies following convulsions. Furthermore, acute pre-treatment (10 minutes) with DNC, but not with naloxonazine alone, antagonized post-ictal analgesia in comparison with control pre-treatment. However, naloxonazine treatment 24 hours before PTZ decreased post-ictal antinociception, but DNC failed to antagonize tonic-clonic seizure-induced analgesia. In addition, according to Racine's index of seizure severity, naloxonazine, DAB-Am-16 dendrimer or DNC did not influence seizure severity when administered either 10 minutes or 24 hours before PTZ. FROM THE CLINICAL EDITOR: This study characterizes the effect of a dendrimer-naloxonazine complex on µ1 receptor-mediated post-ictal antinociception in an animal model of seizure disorder.

Determination of free glycerol in biodiesel at a platinum oxide surface using potential cycling technique.

A novel, inexpensive and fast method based on the electrooxidation of glycerol on platinum electrodes by the potential cycling technique has been designed for the determination of free glycerol in biodiesel. A wide range of linearity was achieved between 15 and 150 mg L(-1) (0.16 and 1.6 mmol L(-1)), which corresponds to concentrations ranging between 56 and 560 mg kg(-1) (glycerol:biodiesel) for an extraction using 2g biodiesel. A method for the fast extraction of glycerol from biodiesel with water followed by elimination of organic interferents has also been developed, so that the novel determination method can be applied to various biodiesel samples. The excellent repeatability allows determination of glycerol in numerous samples, with no need for recalibration.

Determination of potassium ions in biodiesel using a nickel(II) hexacyanoferrate-modified electrode.

In this work, nickel hexacyanoferrate-modified electrode was developed to determine potassium ions in biodiesel by potentiometry. The modified electrodes exhibit a linear response to potassium ions in the concentration range of 4.0 x 10(-5) to 1.0 x 10(-2) molL(-1), with a detection limit of 1.9 x 10(-5)mol L(-1), and a near-Nernstian slope (53-55 mV per decade) at 25 degrees C. The method developed in this work was compared with flame photometry and the potassium concentration found in biodiesel showed that the modified electrode method gives results similar to those obtained by flame photometry.

Simultaneous determination of zinc, copper, lead, and cadmium in fuel ethanol by anodic stripping voltammetry using a glassy carbon-mercury-film electrode.

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-microm 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(-9)-10(-8) mol L(-1) 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.