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h i g h l i g h t s " Galvanised and carbon steels have proven to be compatible with biodiesel. " Biodiesel properties were not affected for a storage time of 56 days. " Zinc release in non-stabilised biodiesel did not stimulate biodiesel deterioration. " TBHQ was rapidly consumed in the first days of the corrosion immersion test. " TBHQ acted as a corrosion inhibitor and enhanced storage stability of biodiesel. a b s t r a c tThe storage stability and corrosive character of soybean biodiesel stabilised with tert-butylhydroquinone (TBHQ) was investigated through static immersion corrosion tests. Coupons of carbon steel and galvanised steel were immersed in soybean biodiesel with and without TBHQ for 12 weeks. Measurements of total acid number, peroxide value, oxidation stability (Rancimat induction period), metal release, and TBHQ consumption at different stages of corrosion were performed. After 12 weeks of the static immersion test with both steels, the non-stabilised biodiesels presented induction times below the EN 14214 limit (6 h); these results were in agreement with increase in the peroxide values. Zinc release was only detected in the non-stabilised biodiesel exposed to galvanised steel, whilst iron was not detected in any biodiesel samples exposed to carbon steel. The absence of zinc in the TBHQ-doped biodiesel exposed to galvanised steel indicates that TBHQ may have acted as a corrosion inhibitor. Additionally, TBHQ was rapidly consumed in the first 3 days of experiments, providing evidence of its activity. For a storage period of up to 56 days, both galvanised and carbon steels were shown to be compatible with biodiesel even in the absence of an antioxidant. The presence of zinc (>2 lg g À1 after 28 days of immersion) due to corrosion did not promote biodiesel deterioration.

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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 À1HCl 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.

Room-temperature ultrasound-assisted digestion of biodiesel for stripping voltammetry of metals with adequate recovery values (94–108%) and low residual carbon content is demonstrated.

This work presents the potential application of organic-resistant screen-printed graphitic electrodes (SPGEs) for fuel analysis. The required analysis of the antioxidant 2,6-di-tert-butylphenol (2,6-DTBP) in biodiesel and jet fuel is demonstrated as a proof-of-concept. The screen-printing of graphite, Ag/AgCl and insulator inks on a polyester substrate (250 μm thickness) resulted in SPGEs highly compatible with liquid fuels. SPGEs were placed on a batch-injection analysis (BIA) cell, which was filled with a hydroethanolic solution containing 99% v/v ethanol and 0.1 mol L(-1) HClO4 (electrolyte). An electronic micropipette was connected to the cell to perform injections (100 μL) of sample or standard solutions. Over 200 injections can be injected continuously without replacing electrolyte and SPGE strip. Amperometric detection (+1.1 V vs. Ag/AgCl) of 2,6-DTBP provided fast (around 8 s) and precise (RSD = 0.7%, n = 12) determinations using an external calibration curve. The method was applied for the analysis of biodiesel and aviation jet fuel samples and comparable results with liquid and gas chromatographic analyses, typically required for biodiesel and jet fuel samples, were obtained. Hence, these SPGE strips are completely compatible with organic samples and their combination with the BIA cell shows great promise for routine and portable analysis of fuels and other organic liquid samples without requiring sophisticated sample treatments.

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This work presents the lead determination in aviation (bio)fuels using disposable screen‐printed gold electrodes (SPGEs) adapted on a batch‐injection cell associated with a micropipette for portable analysis. The method involves injections of 200 µL of sample or standard solutions at controlled dispensing rate (4.8 µL s−1) during deposition step (−550 mV for 90 s), followed by anodic‐stripping voltammetry. Either samples treated by sonication or dry‐ashing can be analyzed with detection limits of 0.0071 and 0.0008 µg g−1 Pb, respectively. A single SPGE can be applied for 60 consecutive measurements (or 120 for samples dry‐ashed). The ultrasound‐assisted treatment is faster, safer, and easily adapted for on‐site analyses, especially considering the portable characteristics of commercially‐available potentiostats and batch‐injection analysis cell using SPGEs.