Measurement 169 (2021) 108356 Available online 16 August 2020 0263-2241/© 2020 Elsevier Ltd. All rights reserved. A novel citrus pectin-modified carbon paste electrochemical sensor used for copper determination in biofuel Gustavo Murilo Alves a , Jos´e Luiz da Silva a, b, * , Nelson Ramos Stradiotto a, b a Analytical Chemistry Department, Institute of Chemistry, S˜ ao Paulo State University (UNESP), Araraquara 14800-060, S˜ ao Paulo State, Brazil b Bioenergy Research Institute, S˜ ao Paulo State University (UNESP), Araraquara 14800-060, S˜ ao Paulo State, Brazil A R T I C L E INFO Keywords: Citrus pectin Polysaccharide Carbon paste electrode Stripping voltammetry Bioethanol fuel Copper ABSTRACT This paper reports the construction of a citrus pectin-modified carbon paste electrode (PEC/CPE) which was applied for electrochemical sensitive detection of copper in biofuel. Considering its low cost of production and ease of handling, this novel sensor is a suitable alternative tool for ensuring the quality control of commercial bioethanol. Pectin carboxylic groups presence in the modified electrode helped increase its current response by 32% compared to the unmodified electrode. Under optimized conditions, using differential-pulse anodic strip- ping voltammetry, the analytical curve presented linear range from 5.0 × 10  8 to 1.0 × 10  4 mol L  1 (R = 0.999), with detection limit of 2.5 × 10  8 mol L  1 , quantification limit of 8.3 × 10  8 mol L  1 and sensibility of 0.12 A mol  1 L. The PEC/CPE was successfully applied for copper determination in bioethanol fuel sample where recoveries ≥99% were obtained. The sensor presented good selectivity, reproducibility and repeatability (RSD ≤ 3.6%), with long-term stability over three months (RSD ≤ 6.3%). 1. Introduction The search for materials that are capable of enhancing the sensibility of electrochemical sensors is constantly rising. Over the past few years, a new class of modifiers, known as the polysaccharides, has drawn considerable attention among researchers in electroanalytical chemis- try. Recently, studies published in the literature have reported the use of chitosan, cellulose, pectin and other polymers for the development of new electrochemical sensors, bringing to light new interesting ways of exploring biological modifiers in in the field [1–6]. The polysaccharides are versatile carbohydrates found in a wide range of molecular forms and which can be produced in laboratories [6–9]. Most of the structures of these molecules are acid derivatives that allow the interaction of the molecules with analytes and help boost electrons transfer on the electrode surface thanks to the polar groups present in the molecules [6]. Pectin, a natural sugar, is predominantly composed of galacturonic acid monomers [10,11]; it is widely used as gelling agent, stabilizer, and emulsifier in the food industry [10,12,13]. Pectin is mainly obtained by the solubilization of protopectin from apple bagasse and citrus peel; the process is carried out in slightly acidic conditions under heating [13]. Brazil is the world leader in the production of orange fruit and juice, followed by USA and China [14–16]. However, an issue of great concern faced by the orange fruit and juice producing and processing industries is that nearly half of the weight of solid orange fruit and liquid juice is lost as sub-products in the production process [12,17–20]. The orange fruit residues are generally pelleted and destined to animal supple- mentation due to the large amount of fiber and nutritional properties in them [18–20]. Pectin extraction from orange peel for use in electro- chemical methods is an interesting environmentally friendly application for orange bagasse. Interestingly, this application has not yet been re- ported in the literature related to techniques for ensuring the quality control of bioethanol. Carbon paste electrodes (CPE) modified with polysaccharides were initially developed by Wang et al. for the determination of copper and lead in water using cyclic voltammetry (CV) and differential-pulse vol- tammetry (DPV) [21]. The method developed based on pectic and alginic acids-modified carbon paste electrode presented poor detection limit for copper and lead, respectively. In another related study, Vilhena et al. [11] used acid/base poten- tiometric titration, differential pulse polarography (DPP) and square- wave voltammetry (SWV) for copper and pectin interaction study. These authors showed that the interaction of pectin with copper is given by the binding of 2 mol of carboxyl groups (COO  ) with each mol of * Corresponding author. E-mail address: jose.l.silva@unesp.br (J.L. da Silva). Contents lists available at ScienceDirect Measurement journal homepage: www.elsevier.com/locate/measurement https://doi.org/10.1016/j.measurement.2020.108356 Received 26 May 2020; Received in revised form 10 August 2020; Accepted 11 August 2020