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This work investigates the oxidative stability and corrosivity of residual cooking oil (RCO) methyl biodiesel exposed to metallic coupons (copper and carbon steel) under simulated storage conditions (static immersion for 90 days within closed vessels) and the effect of antioxidants (tert-butylhydroquinone, curcumin, propylgallate, and butyl-hydroxyanisole) on biodiesel and metallic surfaces. The induction period measured during the experiment showed that all antioxidants retarded biodiesel degradation due to their antioxidant properties. Scanning-electron microscopy and X-ray diffraction of the metallic surfaces revealed the presence of oxides due to the corrosion by biodiesel in absence of antioxidants. Nevertheless, the presence of carbonaceous solids over the metallic surfaces was found which evidences the anticorrosive properties of the antioxidants, confirmed by X-Ray spectroscopy that showed increase in the content of carbon and oxygen on the surfaces. Measurements of corrosion rate also confirmed the anticorrosive action of all antioxidants. Hence, this work shows the dual properties of antioxidants acting as free radical scavengers in the RCO biodiesel as well as corrosive inhibitors, with a special performance of propylgallate, probably due to the presence of more hydroxyl groups in its structure that also may facilitate its interaction with the metallic surface.

We show that fused deposition modelling (FDM) 3D-printed electrodes can be used for quality control of fuel bioethanol. 3D-printing using carbon black/polylactic acid (CB-PLA) filaments resulted in conductive and biodegradable electrodes for biofuel analysis. As a proof-of-concept, copper determination in fuel bioethanol was performed, as such ions catalyse oxidation processes during storage and transport. Square-wave anodic-stripping voltammetry (SWASV) of copper was achieved after sample dilution in 0.1 mol L−1 HCl as supporting electrolyte (resulting in 30:70% v/v ethanol:water). The linear responses were in the range between 10 and 300 μg L−1 (R = 0.999), inter-day precision was lower than 8% (n = 10, for 20 μg L−1) and limits of detection (LOD) and quantification (LOQ) using 180 s as deposition time were 0.097 μg L−1 and 0.323 μg L−1, respectively. Recovery values between 95 and 103% for the analysis of bioethanol spiked with known amounts of copper were obtained. These results show great promise of the application of 3D-printed sensors for the quality control of biofuels.

Environmental concerns caused by the constant use of fossil fuels can be solved by the use of biofuels. This work shows the application of the oil of Trichilia emetica Vahl (Mafura) seeds originati...

Herein, we report the improved detection of Zn2+ via square-wave anodic stripping voltammetry utilizing an electrochemically treated screen-printed gold electrode. Surface analysis of the gold surface revealed increase in rugosity, removal of residual polymeric ink, and consequent higher access to gold microparticles after electrochemical treatment which resulted in improved response for Zn2+ (detection limit of 2.5 μg L− 1). The intra- and inter-electrode precision values were calculated as 3% (n = 10) and 12.5% (n = 3), respectively, applying − 0.9 V for 90 s under stirring of 1000 rpm for pre-concentration of Zn2+ (step potential: 4 mV; amplitude: 50 mV, frequency: 50 Hz) in 0.04 mol L− 1 Britton-Robinson buffer (pH 7.0) as the background electrolyte. Satisfactory recovery values ranging 96 to 104% were achieved for the analysis of struvite (spiked sample). Therefore, the proposed sensor provides precise and accurate direct analyses, without interference from other metals, with rapid responses enabling on-site analyses.

The corrosive character of Moringa oleifera Lam biodiesel was evaluated through static immersion tests with different carbon steels (CS1015 and CS4140) in absence and presence of the antioxidant tert-butylhydroquinone (TBHQ), at room temperature in the absence of light for 84 days. Biodiesel parameters, including oxidation stability (induction period, IP), total acid number (TAN) and iron concentration released from carbon steel, were monitored. The produced biodiesel presented an IP value of 4.9 h, which was increased to 6.2 h after the addition of 500 mg kg−1 TBHQ. After 84 days of immersion, IP values decreased in the first 21 days due to the contact with the metallic coupon, while TBHQ retarded this process. TAN value increased in 20% but the values were below the recommended limits ( 3 h) by the high Fe content.

The presence of Fe(III) can catalyse fuel degradation processes, providing their inefficient burning and increasing the emission of harmful gases into the atmosphere. Thereby, Brazilian National Petroleum Agency establishes a strict limit for the maximum concentration of iron in fuel bioethanol (5 mg kg−1 that corresponds to 6.18 mg L−1), usually monitored by atomic absorption spectrometer. The main subject in this work was to determine the concentration of iron (Fe3+) in bioethanol fuel using the digital image method as a simple analytical methodology. Colorimetric determination was performed by Color Grab app in its RGB (red, green and blue) matrices, installed on a Smartphone. Fe(III) determination was based on its ability to complex with thiocyanate (SCN−) generating a red complex (Fe(SCN)2+). The correlation between Fe(III) concentration and color intensity was obtained after the transformation of RGB components into a grayscale model. A linear response was observed in the concentration range between 0.5 and 10 mg L−1 (R2 = 0.998) with a detection limit of 0.1 mg L−1. Recovery values between 97% and 105% were obtained for the analysis of spiked fuel bioethanol samples. The results agreed with those obtained by spectrophotometry. Repeatability (n = 10) of 2.1% and 1.3% was obtained for the determination of 1 and 4 mg L−1 of Fe3+, respectively. This work demonstrates that smartphone-based methods provide great promise for in-field fuel quality control.

This work presents the association of cloud point extraction (CPE) and electroanalysis for the selective and sensitive determination of methyl parathion (MP) in honey. The CPE step provided the pre-concentration of MP from a complex sample, in which the optimized extraction parameters (Triton X-100 concentration of 0.75% w/v, NaCl concentration of 1.0% w/v and heating time of 30 min) were investigated using a factorial design (23). The detection of MP was performed using a cathodically pre-treated boron-doped diamond (BDD) working electrode and square wave voltammetry (SWV), after a suitable dilution of the CPE extract in Britton–Robinson buffer pH 6.0 as the supporting electrolyte. MP presented three electrochemical processes over the BDD surface, but only the reduction peak at around −0.7 V was monitored for the MP determination (higher detectability). Improved reproducibility was reached by applying an in situ cleaning step (+2.0 V for 15 s) followed by a re-activation process (−2.0 V for 15 s) between measurements. Using the optimized variables, a linear range between 0.1 and 2.0 μmol L−1 was obtained for MP with a limit of detection of 0.006 μmol L−1, a 6-fold lower value when compared with the value attained without the CPE step. The experimental enrichment factor of MP was 6.1. Also, the optimized CPE allowed the determination of MP in honey samples with good accuracy (recovery between 94 and 106%), which was not possible using direct detection (without CPE) due to the matrix interference. This is the first paper that demonstrates the combination of CPE and electroanalysis for the determination of an organic compound.

This work presents a simple and sensitive method to measure in situ free Cu(II) ions in biodiesel using organic-resistant screen-printed gold electrodes (SPGEs) and demonstrates the direct correlation of the content of Cu(II) ions with oxidation stability of biodiesel. Biodiesels contaminated with copper due to corrosion, spiking with standard solutions, and naturally occurring from the oil source, were analyzed after simple dilution in 90% (v/v) ethanol and 10% (v/v) water containing 0.1 mol L−1 HCl as electrolyte (final concentration). Square-wave anodic stripping voltammetry under hydroethanolic media enabled the determination of Cu(II) ions in biodiesel, while the total Cu content was determined by atomic absorption spectrometry. The Rancimat method measured the oxidation stability of biodiesels based on induction period (IP) values, and the results indicate a decrease in IP values due to the catalytic effect of copper in biodiesel, which present direct correlation with the free content of Cu(II) rather than the total copper content. Hence, we recommend the measurement of free metal ions in biodiesel to predict its lower oxidation stability using disposable SPGEs for in-loco analysis. This voltammetric sensor responds to Cu(II) ions in hydroethanolic media for 80 consecutive measurements before its replacement and it is considered highly-repetitive (RSD

Energy demand for modern society is ubiquitous and the liquid fuels play important role in this context. The market acceptance of liquid fuels depends on a highly rigorous quality control, which requires accurate and precise analytical methods to monitor the chemical parameters established by regulatory agencies. Fast and on-site monitoring of the quality parameters of fuels can be achieved by electrochemical techniques using disposable sensors, such as screen-printed electrodes (SPEs). This revision is devoted to recent development and application of SPEs to monitor quality parameters of liquid fuels (fossil fuels and biofuels), including the determination of organic and inorganic analytes using voltammetric or amperometric detection. Trends of SPE technology for quality control of fuels, based on the reported electrochemical methods that may be considered by regulatory agencies, are highlighted.

This work reports the use of eucalyptus pulp as an adsorbent for metal removal from biodiesel. Fatty acid methyl esters produced from sunflower oil (SfMB) and recycled used cooking oil (RMB), which contained Fe, Mn, and Cu, were treated through filtration on a column filled with the cellulosic adsorbent, and washed with deionized water for comparison. The treatment with cellulose material resulted in the removal of 13–81%, 35–84%, and 40–74% of Fe, Mn, and Cu in biodiesels, while the water washing removed 4–40%, 10–47%, and 4–19%, respectively. In addition to the higher efficiency, the use of cellulose is a more environmentally friendly process than the purification with water, once the latter results in a considerable volume of effluent requiring treatment prior to disposal, besides the high consumption of water. Moreover, the regeneration of the cellulosic adsorbent is demonstrated.

A high oxalate uptake from the diet is thought to play a role in the development of hyperoxaluria, a documented risk factor in the formation of calcium oxalate kidney stones. In this sense, a flow system designed with multicommutation is proposed for spectrophotometric determination of oxalate in tea. The procedure is based on the SPADNS method (a complex of zirconium and the trisodium salt of 1,8-dihydroxy-2-(4-sulfophenylazo)-naphthalene-3,6-disulphonic acid), in which the oxalate reacts with the zirconium to form a colorless complex, thus bleaching the red color in a proportional amount to the oxalate concentration. A manifold with three solenoid micro-pumps was used and the decrease in the absorbance of Zr-SPADNS reagent is linear with oxalate concentration in the range of 1.0 to 6.0 mg L−1. The coefficient of variation, sampling rate and detection limit were estimated as 2.6% (4.0 mg L−1, n=10), 120 samples h−1, and 0.30 mg L−1 (99.7% confidence level), respectively, with reagent consumption estimated as 70 μg of SPADNS per determination. Under optimized conditions, no interference was observed in presence of fluoride for the concentration expected in infusions (less than 100 μg L−1). The procedure was applied in different sample infusions included black, green and white tea. The recovery values were between 83 and 108% showing that the proposed protocol is able to determination of oxalate without interference problems in a complex sample after a simple dilution.

The request for energy is a constant concern of the modern society aiming for the maintenance of commercial, agricultural, and industrial activities. On the other hand, petroleum reserves are diminishing and, at the same time, there is an increasing concern on the environmental pollution worldwide caused by the emission of fossil fuels. Therefore, the development of greener sources of energy is highly demanded. Biofuels, solid, liquid, or gaseous fuels produced from biomass, are essential for the development of a sustainable society. The introduction of biofuels as a replacement of fossil fuels in several activities in which an energy source is required is already a common reality in many countries. The commercialization and market acceptance of biofuels depends on a rigid quality control of the final product. In this way, the monitoring of chemical species in biofuels among several other physical-chemical parameters, as well as in fossil fuels, is of key importance to guarantee the quality control of the fuels. Some of these parameters are required to be measured on-site in order to obtain a positive confirmation of commercialization and use of the biofuel. One of the main advantages of electrochemical sensing is the feasibility of performing analysis on-site due to the portable instrumentation. Another relevant advantage of electrochemical sensing is high sensitivity and selectivity, especially achieved with the use of nanomaterials. The modification of electrodes with nanomaterials, such as carbon nanotubes, graphene, nanostructured metals, or metal oxides, has been reported to produce electrochemical sensors of high sensitivity and selectivity with application to a wide range of chemical species in different samples, including the analysis of fossil fuels and biofuels. The aim of this book chapter is to describe how electrochemical sensors act on sensing the nanomolar to micromolar concentrations of trace metal species of environmental and energy interests and present a comprehensive review of examples of such applications presented in the last 5 years.

This work shows that the electrochemical activity of a 3D-printed electrode fabricated using a conductive composite of polylactic acid (PLA) containing carbon black (CB) can be substantially improved through a simple and fast chemical/electrochemical pretreatment in 0.5 mol L−1 NaOH. Scanning electron microscopy and infrared spectroscopy data showed that the pretreatment process promotes the removal of the non-conductive PLA material, providing greater exposure of the conductive particles. Cyclic voltammetry of the redox probe ferricyanide/ferrocyanide indicated faster electron transfer on the treated 3D-printed surface and increase in electroactive area. Moreover, electrochemical impedance spectroscopic results also confirmed faster electron transfer after surface pretreatment. As a proof-of-concept, a low-cost and sensitive method for the determination of cadmium and lead in real urine and saliva samples by square-wave anodic stripping voltammetry was developed. The chemical/electrochemical treatment provided an impressive 30-fold current increase in the detection of both metals. Acceptable limits of detection (2.9 μg L−1 for Cd2+ and 2.6 μg L−1 for Pb2+), wide linear ranges for both metals (30 μg L−1 to 270 μg L−1; R = 0.997), high stability (RSD lower than 4.5%; n = 10), and adequate recovery values (between 93% and 112%) for the analysis of spiked samples were achieved. Additionally, interday (n = 3), intra-day (n = 3), inter-electrode (n = 2) and inter-treatment (n = 2) experiments revealed RSD values lower than 6.5%, which indicates high reproducibility of the proposed treated 3D-printed electrode. The strategy here proposed opens up new applications for 3D-printed electrode in analytical electrochemistry with improved electrochemical sensing properties in comparison to screen-printed electrodes.

The electrochemical oxidation of fipronil is investigated on unmodified and multi-walled carbon-nanotube (MWCNT)-modified glassy carbon electrodes (GCEs), and its amperometric determination using batch injection analysis (BIA) is demonstrated. An oxidation peak was observed at 1.5 V in a 0.1 mol L−1 HClO4/acetone solution (50:50, v/v) on both surfaces. Although MWCNT-modified GCE provided greater sensitivity, the unmodified GCE showed low RSD value, wider linear range, and reduced adsorption of fipronil or its oxidized products on the electrode surface. A detection limit of 4.7 μmol L−1 and linear range of 25–300 μmol L−1 were obtained using a bare GCE. The method was applied in veterinary formulations with results in agreement with those obtained by high-performance liquid chromatography.

This work proposes the use of eucalyptus pulp as an adsorbent for biodiesel purification. Methyl sunflower biodiesel was produced by alkaline transesterification and passed through a column containing the adsorbent. The evaluated impurities were free glycerol, methanol, water content and alkali metals (Na+, K+, Ca2+ and Mg2+). The cellulose fibers were fractionated by sieving in three fractions (sieve pore sizes of 500, 600 and 1,180 μm). The pulp was characterized by infrared, x-ray diffraction, viscosimetric molecular weight, water content, morphological analysis and fiber content of α-cellulose and hemicelluloses. The size of fibers, mass of adsorbent (0.2 and 1.0 g), column diameter (1.0 and 1.3 cm) and the aid of pressure for filtration (atmospheric or 18 psi) on the impurities removal were also evaluated. The physicochemical characterization of biodiesel was performed following tests in accordance with the limits set by the European Standard for oxidative stability at 110 °C, density at 20 °C, water content, acid value, free glycerol, kinematic viscosity at 40 °C, and residual methanol. The optimal condition was observed using 1.0 g of cellulose in a column of 1.3 cm in diameter under pressure of 18 psi was applied. In this condition the free glycerol, methanol and water content in the permeate presented values of 0.0081 ± 0.0001, 0.268 ± 0.009 % w/w and 636 mg kg−1, respectively. The results indicate that this cellulosic adsorbent is a promising material for biodiesel purification instead of using water washing, avoiding the generation of high wastewater volumes.

This work presents a portable electrochemical system for the continuous monitoring of corrosion inhibitors in a wide range of matrices including ethanol, seawater and mineral oil following simple dilution of the samples. Proof-of-concept is demonstrated for the sensing of 2,5-dimercapto-1,3,5-thiadiazole (DMCT), an important corrosion inhibitor. Disposable screen-printed graphitic electrodes (SPGEs) associated with a portable batch-injection cell are proposed for the amperometric determination of DMCT following sample dilution with electrolyte (95% v/v ethanol + 5% v/v 0.1molL-1 H2SO4 solution). This electrolyte was compatible with all samples and the organic-resistant SPGE could be used continuously for more than 200 injections (100µL injected at 193µLs-1) free from effects of adsorption of DMCT, which have a great affinity for metallic surfaces, and dissolution of the other reported SPGE inks which has hampered prior research efforts. Fast (180h-1) and precise responses (RSD < 3% n = 10) with a detection limit of 0.3µmolL-1 was obtained. The accuracy of the proposed method was attested through recovery tests (93-106%) and the reasonable agreement of results of DMCT concentrations in samples analyzed by both proposed and spectrophotometric (comparative) methods.