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An electrode for monoethylene glycol analysis was developed based on the modification of the surface of the glassy carbon electrode with electrochemically reduced graphene oxide and gold and palladium nanoparticles (GCE/rGO/AuPd-np). Its analytical performance was assessed by determining some analytical figures of merit. Graphene oxide was reduced electrochemically as well as the metal particles with gold deposited by chronopotentiometry and palladium by cyclic voltammetry (CV). The electrode was characterized by MET, TEM and EDS techniques. The study of alcohol behaviour was performed electrochemically using CV technique. The positive synergistic effect of metals provided greater electrocatalytic response, stability and resistance to poisoning. The GCE/rGO/AuPd-np sensor presented a detection limit equal to 31.48 µmol l–1 for a linear range of 89.5–179 µmol l–1 with a linear correlation coefficient of 0.9096 and high stability, not losing response even after 650 cycles. [ABSTRACT FROM AUTHOR]

In this work, we developed a method for the quantification of free glycerol in biodiesel using electrochemical detection and solid phase extraction (SPE). SPE was performed using commercial stationary silica phase cartridges to isolate free glycerol from the combined glycerol (such as acylglycerols) and the methyl esters. The electrochemical method was performed by cyclic voltammetry in KOH solution using a glassy carbon electrode modified with Pd nanoparticles. The electrodeposition of palladium nanoparticles was optimized with a complete 32 factorial design with triplicate at the central point. The analytical performance of the method was evaluated in terms of linearity, limit of detection (LOD), limit of quantification (LOQ), precision (repeatability), and accuracy (recovery). The proposed method exhibits good linearity (R2 = 0.99525). The LOD and LOQ values were determined visually, the LOD was1.00 × 10−6% w/w, and the LOQ was 3.30 × 10−6% w/w, presenting better performance compared with other methods described in the literature. The precision was determined by the relative standard deviation (RSD%), and the values obtained were less than 5%. The recovery ranged between 95.8 and 101%. The proposed method proved to be efficient in the quantification of free glycerol in biodiesel, and the results correlate well with the reference method (GC). The results indicate that the method is presented as an alternative to costly and slow GC-based techniques. [ABSTRACT FROM AUTHOR]

Glycerol is a major byproduct obtained in the production of biodiesel, an important renewable fuel. The presence of free glycerol in fuel can have structural and performance consequences with respect to the engine, making fuel quality control important. The standard method to analyze glycerol in biodiesel is gas chromatography, a time-consuming and expensive technique. In this context, an electrode based on glassy carbon electrodes (GCEs) modified with reduced graphene oxide and core-shell gold@palladium nanoparticles was developed for the determination of glycerol in biodiesel. The free glycerol analysis was performed in the aqueous phase obtained by liquid–liquid extraction from a biodiesel sample. Cyclic voltammetry was chosen as the method for glycerol electrochemical analysis to regenerate active sites and promote greater sensor stability. The modified Au@Pd/rGO/GCE electrode showed an excellent performance, obtaining a linear range of 18.2 to 109 µmol L−1 with a correlation coefficient of 0.9895, limits of detection and quantification of 5.33 and 17.6 µmol L−1, respectively, high stability during 1000 cycles, and recovery values of 86% and 87% in the quantification of glycerol in biodiesel samples. The proposed method proved to be a great alternative for the analysis of glycerol in biodiesel, being a fast, sensitive, and low-cost technique due to its high stability and the use of small quantities of reagents. [ABSTRACT FROM AUTHOR]

Urine and struvite are organic fertilizers that have all nutritional requirements for the growth of a plant. However, these fertilizers may contain some emerging organic contaminants, such as ethinylestradiol, which is one of the most common hormones found in aquatic environments and can cause several changes in living organisms. Thus, the present study developed a fast, sensitive, inexpensive, and portable method for determining ethinylestradiol in urine and struvite, using square wave voltammetry (SWV) and screen-printed carbon electrodes modified with electrodeposited nickel film (SPCE-Ni). The electrodeposition of the nickel film on the screen-printed electrode was performed by cyclic voltammetry and optimized using complete factorial design 23 and central composite design. The parameters optimized for SPCE-Ni were: number of cycles (1000); scan rate (5 V s−1) and Ni2+ concentration (9.4 mmol L−1). The operational parameters of the SWV for ethinylestradiol analysis were also optimized by experimental designs and obtained the following optimal values: step potential (10 mV), modulation amplitude (40 mV), and frequency (20 Hz). The method used 0.1 mol L−1 BR buffer (pH 8.0) as support electrolyte and presented a limit of detection of 0.052 µmol L−1 (R2 = 0.996). Ethinylestradiol recovery test in struvite, human urine, synthetic urine, and pharmaceutical tablets ranged from 93.9% to 107.5%, indicating that there is no matrix effect. Furthermore, an interference test was performed with several drugs did not show any significant changes in the ethinylestradiol analytical signal, guaranteeing a greater precision of the method. These results reinforce the possibility of applying the proposed method in loco with a practical and fast way, without the need to use significant amounts of sample. ga1 • In loco monitoring of emerging contaminants using green chemistry practices. • Ethinylestradiol determination in organic fertilizers (urine and struvite). • Simple, fast, and very low reagent consumption (µL) electroanalytical method. • Portable equipment associated with modified screen-printed carbon electrodes. [ABSTRACT FROM AUTHOR]

A statistical treatment was carried out on electrochemical methods intended for iodide determination as a tracer in seawater reservoirs. Comparison was made for amperometric and potentiometric detection, including the use of a modified carbon electrode. The potentiometric method showed a good linear correlation coefficient (r = 0.9926) with a Nernstian behavior in a concentration range of 10 − 5 to 1 mol L − 1 (1.3 mg L − 1 to 127 g L − 1 ) and a limit of detection of 1.3 mg L − 1 (10 μmol L − 1 ). The amperometric method showed a good linear correlation coefficient (r = 0.9988) with a linear response over a concentration range of 1 to 4 mg L − 1 (8 to 31.5 μmol L − 1 ) and a limit of detection of 0.5 mg L − 1 (4 μmol L − 1 ). The statistic treatment has shown that the potentiometric method is promising to measure the iodide concentration in samples with high iodide content and the amperometric method is appropriate to measure the iodide concentration in samples with low iodide content, for example, in the case of produced water from petroleum reservoirs. Moreover, the salophen modified electrode can be readily used for routine analysis in laboratory. [ABSTRACT FROM AUTHOR]

• Selectively determination of ascorbic acid using molecularly imprinted polypyrrole. • Determination of ascorbic acid in presence of dopamine and uric acid interferers. • Molecularly imprinted polypyrrole rough surface favors recognition of the analyte. • Molecularly imprinted polypyrrole-graphene electrode induces electrocatalysis. Molecularly imprinted polymers are pushing the limits of sensing capabilities in electrochemical sensors. As a result, these sensors are driving the improvement of chemical species detection with applications in pharmaceutical, chemical and food industries as well as showing potential for bioanalytes sensing for applications in medical diagnostics. In particular, molecularly imprinted polymer-graphene sensors have great potential to increase the selectivity, sensitivity and detectability of electrochemical sensors for organic molecules determination, especially in the presence of interferers. In this work, we tested three different coatings on glassy carbon electrode for the purpose of ascorbic acid quantification: graphene, molecular imprinted polypyrrole-graphene and non-imprinted polypyrrole-graphene. Among the prepared electrodes, non-imprinted and molecularly imprinted polypyrrole on graphene, exhibited the highest sensitivity to ascorbic acid (6.14 and 5.87 μA/mmol L−1, respectively), although their detection limit (0.56 and 0.10 mmol L−1, respectively) was poore than the uncoated graphene one (0.02 mmol L−1). Besides that, graphene modified glassy carbon electrode showed better response for repetitive uses. However, in the case of a unique measurement to detect the presence of ascorbic acid in a solution containing interferers, as uric acid and dopamine, molecular imprinted polypyrrole-graphene electrode exhibits better response and selectivity in addition to, an electrocatalytic effect. [ABSTRACT FROM AUTHOR]