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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. [ABSTRACT FROM AUTHOR]

Trace amounts of copper decrease significantly the oxidative stability of biodiesel while antioxidants, mostly tert -butylhydroquinone (TBHQ), are commonly introduced to the biofuel to guarantee induction period values within regulatory limits. Hence, a simple method to monitor the most used antioxidant and the most deleterious contaminant in biodiesel can give a fast response on its quality. In this context, this work presents a simple, efficient, low cost and sensitive method for the simultaneous and direct determination of copper and the antioxidant TBHQ in biodiesel. The biodiesel samples were diluted in 90% (v/v) ethanol and 10% (v/v) water containing 0.1 mol L−1 HCl (final concentration) as the supporting electrolyte generating a homogeneous mixture in which Cu(II) and TBHQ were directly detected using the square wave voltammetry (SWV) on a gold working electrode. The presence of biodiesel in the selected electrolyte facilitated the separation of analyte peaks facilitating the treatment of data and quantification. The linear responses for the simultaneous determination were in the range between 5 and 100 μg L−1 and 4.2–81.5 mg L−1 for copper and TBHQ (R > 0.997), respectively. High precision (RSD = 4.0% and 3.9%, n = 20) and limit of detection (LOD) values of 0.31 μg L−1 and 1.0 mg L−1 (0.030 μg g−1 and 0.102 mg g−1 in biodiesel) for Cu(II) and TBHQ, respectively, were obtained. Recovery values between 97% and 104% for both copper and TBHQ were obtained. Image 1 • Rapid method for simultaneous determination of copper and the antioxidant TBHQ in biodiesel. • Biodiesel aliquot 100-fold diluted in hydroethanolic electrolyte with 0.1 mol L−1 HCl in the cell. • The presence of biodiesel facilitated the separation of the voltammetric peaks of analytes. • LOD values of 0.030 μg g−1 and 0.102 mg g−1 in biodiesel for Cu(II) and TBHQ, respectively. • Fast protocol to identify metallic contaminants and attest the required presence of TBHQ. [ABSTRACT FROM AUTHOR]

Abstract 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 (<0.5 mg g−1 KOH according to EN14214). Iron was detected in the biodiesels exposed to CS1015 (8 μg g−1), while in the presence of TBHQ this value decreased to 5 μg g−1, indicating corrosion inhibition by TBHQ. Iron was not detected in the biodiesels exposed to CS4140, which indicated that this material was more compatible with biodiesel. Notably, the oxidation stability of Moringa biodiesel was not affected (IP > 3 h) by the high Fe content. Highlights • Static immersion corrosion test to simulate storage conditions of Moringa biodiesel. • Carbon steels of varied composition were evaluated and metal release measured. • Oxidation stability of biodiesel decreased as corrosion started. • The antioxidant TBHQ retarded the corrosion as iron release decreased. • Addition of TBHQ is required to extend storage stability of Moringa biodiesel. [ABSTRACT FROM AUTHOR]

Abstract 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. Highlights • Screen-printed electrodes (SPE) for on-site quality control of fossil fuels and biofuels. • Voltammetric and amperometrci detection of (in) organic contaminants and additives. • Regulatory agencies define severe limits to substances that can be detected on SPE. • Substrate material and chemical modifiers selected to be compatible with liquid fuels. • Perspective on new platforms to detect adulteration and for quality control on-site. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a simple electrochemical method for Hg determination in fish oil capsules using anodic stripping voltammetry (ASV) on a screen‐printed gold electrode (SPGE). Samples were treated in an ultrasonic bath for 15 min in the presence of a 1 : 1 (v/v) concentrated HCl/H2O2 mixture at room temperature. The limit of detection (LOD) was estimated as 0.25 μg L−1 (corresponding to 7.6 μg kg−1 of oil) with a linear range between 5 and 400 μg L−1 (90 s of deposition time). The analyzed fish oil samples presented Hg concentration below the LOD value. Recovery values for samples spiked with oil standard containing Hg ranged from 95 to 105 %. The method is precise (inter‐day and intra‐day RSD<4 % for n=3) as well as the SPGE sensors (RSD=4.3 %, n=3), which were used continuously (around 100 analyses without replacement) under such oxidation media. The proposed method is feasible to be applied for on‐site determinations due to the portability of sensing and sample treatment approaches. [ABSTRACT FROM AUTHOR]

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 0.1 mol L -1 H 2 SO 4 solution). This electrolyte was compatible with all samples and the organic-resistant SPGE could be used continuously for more than 200 injections (100 µL injected at 193 µL s -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 (180 h -1 ) and precise responses (RSD < 3% n = 10) with a detection limit of 0.3 µmol L -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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. • Free radical scavenging and corrosion inhibition by antioxidants in biodiesel from residual oil. • Immersion tests using copper and carbon steel coupons prove this dual effect of antioxidants. • Higher induction period values by propyl gallate (PG) in biodiesel exposed to both metals. • PG also showed higher anti-corrosive properties in this biodiesel under simulated storage. • Protective layers of carbonaceous solids over metals were formed in biodiesel with antioxidants. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biodiesels with low oxidation stability (OS) were blended with soybean biodiesel. [•] Residual cooking oil and cottonseed oil biodiesels had their OS improved. [•] Sunflower oil biodiesel had its OS improved by blending with colza oil biodiesel. [•] Binaries mixtures meet ASTM D6751 and EN 14214 requirements of OS values. [Copyright &y& Elsevier]

• Noteworthy multi-pumping flow system was designed for determination of oxalate using SPADNS method. • The procedure presents as an advantageous alternative to traditional and manual methods. • The possibility to develop more ecological analytical procedures is shown in this work. • The proposed procedure was applied to tea beverages without any pretreatment. 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. Image, graphical abstract [ABSTRACT FROM AUTHOR]