β-agonist residues in animals can cause serious menaces to human health, such as muscle tremors, vomiting, headaches, central nervous system, cardiovascular, and food poisoning diseases [1]. Therefore, the use of β-agonists as redistribution agents in meat-producing companies is strictly prohibited in many countries [2]. Among these, one of the most widely used β2 adrenergic agonists in the treatment of bronchial asthma is salbutamol (SBT, 2-(tert-butylamino)-1-(4-hydroxy-3-hydroxymethyl) phenylethanol), also known as albuterol [3]. SBT has been illegally used as a lean meat extract (or growth promoter) to improve muscle weakness and growth rate, decrease fat content, and enhance the conversion efficiency of feed in animals [4, 5]. Therefore, such use of SBT leads to its accumulation in animal tissues and transmission to humans through the consumption of meat products contaminated with SBT. Excessive accumulation of SBT in humans can cause acute toxic responses in humans, such as heart palpitations, low blood potassium, and high blood sugar levels [6]. On the other hand, SBT has potential pharmacological activity as a phenylethanolamine or β-agonist, and it is generally used in the treatment of exercise-induced and allergic asthma as well as a chronic obstructive type of pulmonary disorder [4].
Sensitive, accurate, and fast determination of SBT in both pharmaceutical and meat or feed samples is of great importance. For this purpose, various analytical approaches have been reported based on chromatographic techniques such as liquid chromatography-tandem mass spectrometry [7, 8], and high-performance liquid chromatography-UV spectrometry [9]. Although the chromatographic methods enable both quantitative and qualitative determination of SBT with remarkable acceptability, reproducibility, and sensitivity, they include high-priced instrumentation, complex sample preparation and operating procedures, and long-time detection cycles. In addition, they cannot provide a practice solution route for real-time measurement and fast determination of large quantities of samples [10]. Nowadays, electroanalytical techniques are of great interest to researchers due to their several advantages, such as low detection limits, high analyte selectivity and sensitivity, simplicity in the sample preparation step, cost-effectiveness, adaptability to field use, and minimal use of toxic organic solvents [11].
The remarkable detection sensitivity and efficiency of an electrochemical sensor are mostly dependent on the electrocatalytic activity of the electrode and modification materials. Recently, pencil graphite rods have been frequently used as an efficient electrode material because the obtained pencil graphite electrodes (PGEs) offer some advantages such as disposability, low cost, mechanical rigidity, simplicity, commercial availability, and ease of surface modification over other carbon-based or solid electrodes [12–15]. In addition, a large number of nanomaterials have been utilized in the preparation of modified electrodes and the construction of electrochemical sensors for signal amplification [16]. In this sense, carbon nanotubes (CNTs) as a modification material have received great interest in the preparation of modified electrodes due to their significant mechanical strength, high electrical conductivity, high surface area, and good chemical stability properties [17]. Thus, they provide outstanding catalytic activity, resulting in the facilitation of electron transfer reactions as well as offering a wide range of operating potentials [18]. Another modification material, Nafion (Nf), is a perfluorosulfonated polymer with high mechanical stability. It has been extensively used in the modification of electrode surfaces due to its thermal stability, good mechanical strength, cation exchange, chemical inertness, and poor passivation features [19]. Nf-film-based materials have been widely used in the construction of electrochemical sensors and biosensors due to the excellent functions mentioned above [19]. Besides the use of modified carbon-based electrodes such as glassy carbon electrode (GCE) with Nafion/CNT composite in electroanalytical determinations [17–22], its combination with PGE has recently been used as an effective modified electrode in various electroanalytical approaches, such as the determination of Pb(II), Cd(II), and glucose [23, 24].
Several studies have been carried out for the electrochemical determination of SBT based on the use of different electrodes and modification materials. [4, 6, 10, 25–39]. In these studies, various composite nanomaterial-modified carbon-based electrode platforms, such as GCE, carbon paste electrode (CPE), and screen-printed carbon electrode (SPCE), have been successfully utilized for the electrochemical determination of SBT. However, GCE and CPE involve laborious and time-consuming hard cleaning and surface polishing or preparation steps at the end of each measurement as well, and they have a high cost compared to PGE. SPCE is disposable, but its surface is not as renewable as in PGE, and it is also more expensive than PGE [12]. Compared with these traditional electrodes, the advantageous PGE has not been used in the studies carried out for the electrochemical determination of SBT yet. The voltammetric determination of SBT has been performed using easily prepared disposable, low-cost electrodes, Nf/f-MWCNTs/PGE for the first time. The sensitive and selective detection of SBT with the combination of three advantageous materials, PGE, MWCNTs, and Nf, constitutes the novelty of the proposed study.