Development of a Novel and Simple Electroanalytical Procedure for the Determination of Copper in Biofuel Employing a Sensor Based on Vulcan Functionalized with Carbazone

A novel and simple electroanalytical method for the determination of Cu2+ in biodiesel samples by stripping voltammetric analysis was developed. The method employs a carbon paste electrode (CPE) modified with Vulcan carbon, previouly functionalized with carbazone (CBZ). The CPE/Vulcan-CBZ sensor promoted a significant increase in the analytical signal obtained from copper as compared to unmodified CPE, and the CPE modified with Vulcan carbon (CPE/ Vulcan). Vulcan-CBZ, Vulcan and CBZ materials were characterized by Fourier transform infrared spectroscopy (FTIR) technique. The electrochemical behavior of the sensor was evaluated using cyclic voltammetry (CV) and square-wave anodic stripping voltammetric (SWASV) techniques. The CPE/Vulcan-CBZ modified electrode showed excellent response and was able to detect Cu2+ at nanomolar levels. The electrochemical method is based on preconcentration of Cu2+ ions on the CPE/Vulcan-CBZ at 0.35 V vs. Ag/AgCl(sat) in 0.2 mol L-1 ammonium sulfate solution ((NH4)2SO4), pH 3.5, during 120 s, followed by subsequent chemical stripping. The analytical signal showed a linear response for Cu2+ concentrations in the range from 6 to 190 nmol L-1 (r = 0.998), with a detection limit of 1.2 nmol L-1. The sensor was successfully applied for the determination of Cu2+ in biodiesel and the average recovery varied between 97.0 and 102.8% for the soybean biodiesel samples and between 109.6 and 111.0% for the babassu biodiesel samples showing a good accuracy for the proposed method.

本研究开发了一种新颖且简便的电分析方法，用于测定生物柴油样品中的Cu²+，该方法采用溶出伏安法开展分析。该方法使用经卡巴腙（carbazone, CBZ）预先功能化修饰的瓦尔肯碳（Vulcan carbon）改性碳糊电极（carbon paste electrode, CPE）。相较于未改性的CPE以及仅用瓦尔肯碳改性的CPE（CPE/Vulcan），CPE/Vulcan-CBZ传感器可显著提升铜离子的分析信号。研究采用傅里叶变换红外光谱（Fourier transform infrared spectroscopy, FTIR）技术对Vulcan-CBZ、瓦尔肯碳以及卡巴腙材料进行了表征。通过循环伏安法（cyclic voltammetry, CV）与方波阳极溶出伏安法（square-wave anodic stripping voltammetric, SWASV）技术评估了该传感器的电化学行为。CPE/Vulcan-CBZ修饰电极展现出优异的响应性能，能够在纳摩尔级别检测Cu²+。该电化学方法的操作流程为：在pH为3.5的0.2 mol·L⁻¹硫酸铵（(NH4)2SO4）溶液中，于相对于饱和银-氯化银参比电极（Ag/AgCl(sat)）的0.35 V电位下，将Cu²+离子预富集于CPE/Vulcan-CBZ修饰电极表面120 s，随后进行后续的化学溶出。分析信号在6~190 nmol·L⁻¹的Cu²+浓度范围内呈线性响应（相关系数r=0.998），检出限为1.2 nmol·L⁻¹。该传感器已成功应用于生物柴油中Cu²+的测定，其中大豆生物柴油样品的平均加标回收率介于97.0%~102.8%之间，巴巴苏生物柴油样品的平均加标回收率介于109.6%~111.0%之间，表明所提出的方法具备良好的分析准确度。