Monitoring of Butylated Hydroxyanisole in Food and Wastewater Samples Using Electroanalytical Two-Fold Ampliﬁed Sensor

: A high performance and fast response sensor was fabricated as a monitoring system for the determination of butylated hydroxyanisole (BHA) in food and wastewater samples. In this regard, a carbon paste electrode (CPE) that was ampliﬁed with platinum-decorated single wall carbon nanotubes (Pt/SWCNTs) and 1-Butyl-3-methylimidazolium chloride ([C4mim][Cl]) was investigated as a new electroanalytical sensor for the monitoring of BHA in aqueous solution. The [C4mim][Cl]/Pt/SWCNTs/CPE offered an excellent catalytic activity on oxidation signal of BHA and enhanced its oxidation current about 5.51 times. In the ﬁnal step, the standard addition results conﬁrmed the powerful ability of [C4mim][Cl]/Pt/SWCNTs/CPE to the monitoring of BHA in different water and food samples with acceptable recovery data.


Introduction
The monitoring of food compounds is one of the major steps in the investigation of food quality [1,2]. There are several ingredients in food products that should be studied before use by customers. For many years, due to the close relationship between food quality and human health, measuring and evaluating food quality has been one of the priorities of global organizations [3]. Here, sensors show a significant role in this field, as they gather relevant information from the quality and safety of food products. These data help to create smart food. On the other hand, many of the biomass-derived materials are highly recommended for the fabrication of electro-analytical tools due to their unique features such as sustainability, regenerative nature, and cost-effectiveness [4]. Therefore, sensors and especially electrochemical sensors are a new approach in analytical systems to achieve sustainability goals. Among food additives, antioxidants have been considered more than other additives due to their many benefits and key roles in improving food quality [5]. Tert-butyl-4-methoxyphenol or butylated hydroxyanisole (C 11 H 16 O 2 ) is one of the more commonly used antioxidant food additives that are permitted for application in approximately 50 countries [6]. According to the US Food and Drug Administration reported data, the presence of 0.02% w/w of BHA in the total value food produces is safe and cannot create any problems for human health in low concentrations. However, the National Toxicological Program (NTP) report showed that a high dose of BHA is harmful and can cause cancer. Therefore, controlling the amount of BHA in the food production process is important [7].
Accordingly, measurement methods have been used for many years as a suitable strategy to evaluate the quality of food products [8]. Various measurement methods such as chromatography, spectroscopy, and electrochemical sensors have been proposed to monitor food composition [9][10][11][12][13]. Electrochemical methods have received greater attention than the other techniques [14,15]. Butylated hydroxyanisole is a common antioxidant and is added to edible fats and fat-containing foods [6]. Research studies confirm that high doses of BHA in food products can be hazardous for the human body and the monitoring of its concentration is important in food products. Therefore, some analytical methods such as electrochemical sensors [16], fluorimetry [17], gas-liquid chromatography [18], capillary electrophoresis [19], and high performance liquid chromatograpy (HPLC) [20] were suggested for the electrochemical determination of BHA concentrations.
Electrochemical sensors are one of the biggest branches of sensor tools that create a relationship between electrical signals and the concentration of compounds [21][22][23][24][25]. Electrochemical sensors have many benefits in monitoring biological and food products such as fast response, low cost, easy operation, portability, and easy modification compared to other analytical systems [26][27][28][29]. Electrochemical sensors can be easily modified to create sensitive and selective analytical instruments for monitoring systems [30][31][32]. Recently, electrochemical methods have gained a special place in food and pharmaceutical analysis as an alternative to most measurement methods [31,[33][34][35]. The unique features of electrochemical sensors, such as fast measurement speed and the ability to become portable kits, have led most large companies to accept this technique as a suitable strategy [36,37]. The behavior of electrochemical sensors is relative to the modification process [38][39][40]. In this regard, nanomaterials and ionic liquids have been widely used to modify electrodes [41,42].
Ionic liquids are a group of organic materials with unique properties and high electrical conductivity that have been widely used in the synthesis of chemicals and the catalysis of various chemical reactions as well as electrochemical sensors [63,64]. In recent years, they have been employed as a suitable alternative to paraffin in the manufacture of carbon paste electrodes due to their superior electrical conductivity [64,65]. According to the literature, [C4mim][Cl] is a good conductive mediator for the modification of paste electrodes and is the suitable choice for the fabrication of highly sensitive electrochemical sensors [66].
Based on the explanations that are provided in the previous paragraphs, nanomaterials and ionic liquids have been used as suitable modifiers for electrochemical sensors. Numerous scientific reports have shown that the simultaneous use of these modifiers can create unique features for electrochemical sensors.
In [Cl]/Pt/SWCNTs/CPE can be monitored BHA in low concentrations with a detection limit of 0.5 nM, which is the equivalent to (and in many cases better than) the previously described electrochemical sensors.
Pt/SWCNTs was synthesized by the reported procedure in our previously published paper by polyol strategy [62].

Fabrication of Sensor
The ratio of graphite powder to Pt/SWCNTs nanocomposite and also the ratio of

Instruments
Electrochemical signals were recorded by an electrochemical machine Ivium-Vertex (Netherlands). The recording systems were connected to an Ag/AgCl/KCl sat , Pt wire, and [C4mim][Cl]/Pt/SWCNTs/CPE as the reference, counter, and working electrode, respectively. Transmission electron microscope (TEM) model Zeiss-EM10C-100 KV (Germany) was used for morphological investigation.

Real Sample Preparation
Edible oil, orange juice, and wastewater were selected for real sample analysis. The orange juice and wastewater were centrifuged (3000 rpm) and filtered. Afterwards, 5 mL of the filtered juice or wastewater sample was mixed with phosphate buffer solution (0.1 M pH = 7.0) and used for real sample analysis. The edible oil was prepared by mixing 2 mL of the sample and 20 mL hexane in an erlenmeyer flask, followed by centrifugation at 3200 rpm for 10 min. Following that, 10 mL hexane was added to the sample, and the mixture was shaken for 45 min in the same conditions. In the final step, 2 mL of the extracted sample was dissolved by 2 mL pure ethanol and the sample was mixed with phosphate buffer solution and transferred into an electrochemical cell for real sample analysis.

Charactrization of Modified Electrode
The electrochemical impedance spectroscopic (EIS) method was employed for the characterization of modified and unmodified sensors in the presence of BHA (not shown

pH Investigation
The oxidation signal of BHA was recorded in different pH ranges at the surface of [C4mim][Cl]/Pt/SWCNTs/CPE using the square wave voltametric method. The results were depicted in the inset of Figure 1. Using oxidation peak potentials, a linear relationship was observed between the oxidation potential of BHA and pH with an equation of E = 0.0603 pH + 0.7177 (R 2 = 0.9987) that confirmed a pH-dependent reaction according to Scheme 1 for redox reaction of BHA in aqueous solutions ( Figure 1). As can be seen, with an increasing pH value, the value of protons in the solution was reduced and the redox process was performed more easily and shifted the potential to lower values. On the other hand, the maximum oxidation signal for redox reaction of BHA was observed on pH = 7.0 and this condition was used for the next steps ( Figure 2).

Modification Effect
The SW voltammograms of BHA were recorded at the surface of the amplified and unmodified electrodes. BHA offered the oxidation currents of 5.

Scan Rate Study and Stability Invesigation
The linear sweep voltammograms (LSV) of 700 µM BHA were recorded in the scan rate range 50-300 mV/s (Figure 4 inset). The linear relationship between the oxidation current of BHA and ν 1/2 with an equation of I = 3.3609 ν 1/2 −14.6670 (R 2 = 0.9979) in the scan rate range 50-300 mV/s, suggested a diffusion process for redox reaction of BHA at the surface of [C4mim][Cl]/Pt/SWCNTs/CPE (Figure 4). [Cl]/Pt/SWCNTs/CPE monitoring of BHA were comparable to, and in some cases, were better than the prior recommended sensors (see Table 1).

Selectivity Investigation
In this stage, the selectivity of [C4mim][Cl]/Pt/SWCNTs/CPE for monitoring 10 M BHA was investigated in the presence of certain food and inorganic substances. The results were displayed in Table 2 with an acceptable error rate of 5% in current. As can be seen, the [C4mim][Cl]/Pt/SWCNTs/CPE showed a good selectivity for the monitoring of BHA in an aqueous solution.

Real Sample Analysis
The capability of [C4mim][Cl]/Pt/SWCNTs/CPE for the monitoring of BHA in the real samples was checked by the standard addition methods. For this propose, edible oil and orange juice were selected and prepared according to reported procedure in Section 2. The results were tabulated in Table 3, and the recovery range of 98. 25