Portable potentiometric device for determining the antioxidants capacity published by Ural Federal University eISSN 2411-1414 chimicatechnoacta.ru ARTICLE 2023, vol. 10(1), No. 202310104 DOI: 10.15826/chimtech.2023.10.1.04 1 of 8 Portable potentiometric device for determining the antioxidant capacity Elena R. Salimgareeva a* , Dinara I. Igdisanova a , Daria S. Gordeeva b, Anatoly I. Matern a, Elena. A. Yarkova a, Elena L. Gerasimova a , Alla V. Ivanova a a: Institute of Chemical Engineering, Ural Federal University, Ekaterinburg 620009, Russia b: LLC “ANK-service”, Novouralsk 624130, Russia * Corresponding author: e.r.gazizullina@urfu.ru This paper belongs to the MOSM2022 Special Issue. Abstract At present, the development of portable devices for the express assessment of the content of biologically active objects, such as antioxidants, is one of the relevant technological problems of modern chemistry, medicine, and engineering. The main advantages of such devices are the simplicity and rapidity of analysis, small volumes of analyte, as well as miniaturization of equipment, making it possible to carry out the on-site analysis and, thus, to take a step towards the personalized medicine. The potentiometric method using the K3[Fe(CN)6]/K4[Fe(CN)6] system, which in the laborato- ry-scale version proved to be the most accurate, reproducible, and express, was the basis for the developed prototypes of portable devices. In this study, two versions of prototypes of the portable device are proposed, namely, the open microcell with the 0.2 ml volume and the microfluidic device with flow control. The correctness of the antioxidant capacity (AOC) determination in both systems was confirmed by comparing the results of the "introduced-found" method on model solutions of antioxidants and their mixtures with the AOC results obtained in a standard laboratory elec- trochemical cell. The relative standard deviation did not exceed 10%. The AOC of some beverage industry was determined using the microfluidic de- vice. The correlation coefficient of the results, obtained in the microfluidic device and the laboratory cell, was 0.90, which indicates good data conver- gence and the possibility of using the potentiometric method implemented in the microfluidic device to assess the AOC of multicomponent objects. Keywords portable device antioxidant potentiometry microcell microfluidic device Received: 25.11.22 Revised: 12.12.22 Accepted: 12.12.22 Available online: 21.12.22 Key findings ● The open microcell and the microfluidic device were developed for the determination of the antioxidants capacity of var- ious objects. ● The potentiometric method implemented in the devices allows estimating the AOC of model and multicomponent objects. ● The relative standard deviation of the AOC in the devices did not exceed 10%. © 2022, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). 1. Introduction It is known that the oxidative stress is one of the fac- tors causing the occurrence of many pathological condi- tions in the human body, on the one hand, and accom- panying the course of diseases and causing complica- tions in a large number of diseases, on the other. The risk of the oxidative stress increases in the conditions of the technogenic development of society, the envi- ronmental degradation, the growth of pathological con- ditions of the population. As a consequence the assess- ment of the antioxidants content in various objects, such as food, pharmacy, biological objects, is becoming more and more demanded [1–3]. One of the relevant technological tasks of modern chemistry, engineering and medicine is the transition to the miniaturization of equipment and the creation of port- able devices for personal use. Their undoubted advantages are the simplicity and rapidity of analysis, and small vol- umes of the analyte, which will make it possible to take a http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2023.10.1.04 mailto:e.r.gazizullina@urfu.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0003-1304-0346 http://orcid.org/0000-0003-2203-4546 https://orcid.org/0000-0001-9514-0070 https://orcid.org/0000-0001-7515-3712 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2023.10.1.04&domain=pdf&date_stamp=2022-12-21 Chimica Techno Acta 2023, vol. 10(1), No. 202310104 ARTICLE 2 of 8 DOI: 10.15826/chimtech.2023.10.1.04 step towards personalized medicine. From this point of view, the purpose of this work was the creation of a porta- ble device for the express determination of the antioxidants content in various objects. Currently, a large number of methods have been devel- oped for determining the antioxidant content. Based on the three main mechanisms of antioxidant action in the human body, the existing methods can be classified into the methods based on the reaction of electron transfer from an antioxidant to a reagent (ET-mechanism), the reaction of a hydrogen atom transfer from an antioxidant to a reagent (HAT-mechanism), and the complex for- mation reactions of an antioxidant with metal ions of var- iable valence [4]. The developed methods for determining the antioxi- dant content are quite accurate and informative, but they have disadvantages and limitations, which mainly include the complexity of the methodology and equipment, and the high cost of instruments and reagents. The main disad- vantage of optical methods for determining the antioxi- dant content, which include such well-known approaches as TEAC (Trolox equivalent antioxidant capacity) [5, 6], TRAP (Total radical trapping parameter) [7, 8], ORAC (Ox- ygen radical absorbance capacity) [9], FRAP (Ferric reduc- ing antioxidant power) [10], CUPRAC (Cupric Reducing Antioxidant Capacity) [11], is the difficulty in studying turbid and colored samples. Many methods for assessing antioxidant properties use strong oxidizing agents, or the analysis is carried out in an acidic solution, which, again, makes it difficult to use them for the analysis of objects containing proteins and amino acids. The literature describes works on the creation of de- vices for the transition to miniaturization for some of the methods for determining the antioxidants content: FRAP and CUPRAC, implemented in the form of test strips [12– 14], sensors based on nanoparticles of transition metal oxides (CeO2, Fe2O3, SiO2, etc.) [15–17]. Despite the high reproducibility and accuracy of the analysis results, the devices have disadvantages associated with the difficulty in manufacturing and using them on-site, as well as the use of expensive materials and reagents. For more objective information about the antioxidant properties of objects, it is advisable to use the integrated approach that allows one to evaluate the antioxidant effect by three main oxidation mechanisms [18]. Numerous stud- ies [3, 19] show that, despite the variety of mechanisms of antioxidant action in the human body, the determination of antioxidant content using the ET-mechanism is quite informative and has a high correlation degree with known methods of analysis [18]. In addition, methods based on the ET-mechanism are simple to implement, which has been confirmed by numerous works. Electrochemical methods are among the most promising methods of analysis, characterized by the simplicity of techniques and equipment, and the low cost of devices. The potentiometric method, in contrast with the other electro- chemical methods, is more rapid and sensitive, allows stud- ying turbid and colored samples, and the instrumentation can be implemented in a portable format [20–23]. In this work, the potentiometric method using the K3[Fe(CN)6]/K4[Fe(CN)6] system, which in the laboratory- scale version proved to be the most accurate, reproducible, and express, was the basis for the developed prototypes of portable devices [24]. Our proposed approach for creating the analytical platform for determining the antioxidant content includes the transition from a standard laboratory electrochemical cell to a microcell for the purpose of con- ducting studies in small volumes, and then creating a pro- totype of a microfluidic device. 2. Experimental 2.1. Reagents and objects The following reagents were used in this work: potassium hexacyanoferrate (III) К3[Fe(CN)6] (Sigma-Aldrich, USA), puriss. grade; potassium hexacyanoferrate (II) К4[Fe(CN)6] (Reachim, Russia), puriss. grade; KCl (Sigma- Aldrich), puriss. grade; L- ascorbic acid (Panreac), puriss. grade; L-cysteine (Panreac), puriss. grade.; Glutathione (Panreac), puriss. grade.; Pyrogallol (Panreac), puriss. grade.; Caffeic acid (Panreac), puriss. grade.; Rutin (Pan- reac), puriss. grade.; Quercetin (Panreac), puriss. grade.; Luteolin (Panreac), puriss. grade.; Dihydromyricetin (Pan- reac), puriss. grade.; Phloroglucinol (Panreac), puriss. grade.; Catechol (Panreac), puriss. grade. As objects, mass-produced drinks were investigated: Rich Orange, Sady Pridonia Apple-Cherry, Lyubimiy Peach, Dobry Cherry, Lyubimiy Multifruit, Dobry Apple-Pear, Lip- ton Green Iced Tea, and Coca-Cola Lime. 2.2. Apparatus Potentiometric measurements were carried out using the pH-meter Expert-рН (OOO Econics-Expert, Moscow). EPV-1 redox platinum electrode (Gomelsky ZIP, Gomel, Belarus) and EVL-1M silver-silver chloride electrode (Ag/AgCl/3M KCl) (Gomelsky ZIP, Gomel, Belarus) were used as electrodes when working with the standard labor- atory electrochemical cell, and platinum wire and silver wire coated with an insoluble silver salt – for operation in the microcell and microfluidic device. The design of the microcell and microfluidic device was carried out in Tinkercad for 3D modeling. The devices were printed on the Longer Orange 10 3D printer (Longer, China) using SLA technology, which is characterized by high accuracy, good surface quality, no visible polymer layers, and a wide selection of consumables. The photo- polymer with increased strength characteristics was used as a material. The selection criteria for this polymer resin were: – high speed, accuracy and reproducibility of printing; – the ability to create complex models (including sys- tems of microchannels with thin walls); https://doi.org/10.15826/chimtech.2023.10.1.04 Chimica Techno Acta 2023, vol. 10(1), No. 202310104 ARTICLE 3 of 8 DOI: 10.15826/chimtech.2023.10.1.04 – high level of detail; – resistance to reagents of the system; – easy post-processing. The reagents and samples were introduced into the mi- crofluidic device using the Syringe Pump Model No 1000 (Syringe Pump, NY, USA). 2.3. The potentiometric method of determining AOC The potentiometric method of determining the antioxidant capacity was used with the K3[Fe(CN)6]/K4[Fe(CN)6] oxi- dizing agent to measure the potential of the platinum elec- trode of the K3[Fe(CN)6]/K4[Fe(CN)6] system and after the chemical reaction between the sample antioxidants and the oxidizing agent [24]. The potential change occurs as a result of a chemical reaction in solution (1): 𝑛[Fe(CN)6] 3− + AO = 𝑛[Fe(CN)6] 4− + AOOx, (1) where AO – an antioxidant, АОOx – an oxidation product of antioxidant. The dependence of the potential change on time is shown in Figure 1. Antioxidant capacity (AOC) is calculated as (2–3): AOC = 𝐶Ox − 𝛼 ∙ 𝐶Red 1 − 𝛼 ∙ 𝑛, (2) 𝛼 = ( 𝐶Ox 𝐶Red ⁄ ) ∙ 10 (𝐸2−𝐸1)∙ 2.3∙𝑅∙𝑇 𝑛∙𝐹 , (3) where COx is the K3[Fe(CN)6] concentration, mol/dm3; CRed is the K4[Fe(CN)6] concentration, mol/dm3; E1 is the potential measured before the introduction of a test sam- ple, V; E2 is the potential measured after the addition of the test sample, V, n is the dilution degree. Since potassium hexacyanoferrate (III) satisfies the re- quirements for oxidizing agents that can be used to de- termine antioxidant properties [25], as previously estab- lished, AOC is an integral parameter equal to the total ef- fective equivalent concentration of potassium hexacy- anoferrate (III) that entered in reaction with antioxidants of the analyzed sample. The half-life period (t1/2, s) of the interaction of the studied compound with potassium hexacyanoferrate (III) was calculated from the kinetic curves of the concentra- tion change of the reduced form of iron on time during reaction (1). The half-life period corresponds to the time at which 50% AOC is recorded (AOC1/2 = AOC/2 mol/l) (Figure 2). The experimentally obtained stoichiometric coefficient is calculated as the ratio of AOC to the introduced antioxi- dant concentration (n = AOC/CAO). 2.4. Data treatment The measurements were replicated five times. Statistical evaluation was performed at the significance level of 5%. All data were expressed as X±∆X, where X is the average value and ∆X is the expanded standard uncertainty. The relationship between the results obtained in the microcells and in the standard laboratory cell was calculated using the Pearson correlation. The convergence of the analysis results in micro- and macrocells was assessed using the t-test to compare mean values and the F-test to compare dispersions. 2.5. Quantitation limit The quantitation limit Clim was calculated by a probabilis- tic method [26]. The dependence of the relative standard deviation σ on the average values, in this case, the antiox- idant capacity (AOC), determined by the potentiometric method in the microfluidic device, for the entire concen- tration range, was built for this purpose. The quantitation limit was estimated from the plot of σ = f(Сi) dependence. The Clim value corresponded to the minimum content of the sample component determined by this approach with the relative standard deviation σ = 0.33. 3. Results and Discussion In this work, the determination of the antioxidant capacity in the standard laboratory electrochemical cell and the microsystems was carried out by the potentiometric method using the K3[Fe(CN)6]/K4[Fe(CN)6] system. The following requirements guided the choice of the oxidizer model [25]: – the reaction of electron transfer from AO to the oxi- dant molecule must be thermodynamically possible; Figure 1 Time-dependent potential change when the pyrogallol (С = 0.1 mM) is introduced into the solution of the K3[Fe(CN)6] (0.01 M)/K4[Fe(CN)6] (0.1 mM) system. Figure 2 AOC change with time during the interaction of the py- rogallol with the K3[Fe(CN)6] (K3[Fe(CN)6] (0.01 M)/ K4[Fe(CN)6] (0.1 mM)). https://doi.org/10.15826/chimtech.2023.10.1.04 Chimica Techno Acta 2023, vol. 10(1), No. 202310104 ARTICLE 4 of 8 DOI: 10.15826/chimtech.2023.10.1.04 – the redox potential of the oxidizing agent under the analysis conditions should be between the potentials of active oxygen metabolites and AO, but there should be a certain difference between them; – the reaction rate between the oxidizing agent and the antioxidant must be sufficiently high. In this case, the choice of K3[Fe(CN)6] as a model of an oxidizing agent is substantiated theoretically and experi- mentally as an optimal model for studying the antioxidant properties of compounds according to the electron trans- fer mechanism [27–28]. This method makes it possible to evaluate the redox characteristics of the studied compounds and the thermo- dynamic possibility of their interaction with active oxygen metabolites, which is a rather important parameter in the study of antioxidant properties. The method for evaluating antioxidant properties using potassium hexacyanoferrate (III) as a model of an oxidizing agent was tested on a large number of objects and proved to be accurate, informative, simple, and express [24, 25, 28]. At the first stage, to move towards microvolumes, the open microcell with the 0.2 ml volume, structurally re- peating the form of a standard laboratory electrochemi- cal cell (Figure 3), was developed. The volume and form of the microcell were selected empirically. The potential was recorded using the electrode pair – the platinum wire and the silver wire, electrochemically coated with an insoluble silver salt. The background electrolyte was the 0.1 M KCl solution. The platinum wire was used as a working electrode. The potentials of platinum wire relative to silver wire and silver wire with electrochemically deposited silver chloride were recorded at different ratios of the compo- nents of the oxidized and reduced forms of the K3[Fe(CN)6]/K4[Fe(CN)6] system in the 0.1 M KCl solu- tion to select the reference electrode. High reproducibility, as well as potential stability, was achieved using silver wire coated with electrochemically deposited silver chloride. Thus, all further studies were car- ried out with respect to this reference electrode. The slope of the dependence of the potential on the logarithm of the K3[Fe(CN)6]/K4[Fe(CN)6] concentration ratio in the micro- cell relative to the silver wire coated with electrochemically deposited silver chloride was 57±1 mV/decade (Figure 4). Figure 3 Prototype of the open microcell. Model solutions of antioxidants and their mixtures with known mechanisms of oxidation by the electron transfer mechanism were chosen as analysis objects [29– 33]. It is known that one of the mechanisms of oxidation of ascorbic acid and pyrogallol consists in the transfer of two electrons and two hydrogen atoms (Scheme 1–2). Thi- ol compounds such as the cysteine and glutathione are oxidized to form dimers. In this case, one electron and one hydrogen atom are transferred from one antioxidant mol- ecule (Scheme 3–4). Table 1 presents the AOC values of model solutions of antioxidants and their mixtures in different ratios ob- tained in the microcell. The correctness of the AOC deter- mination was confirmed by the "introduced-found" meth- od, taking into account stoichiometric coefficients, as well as in comparison with the data obtained in the standard laboratory electrochemical cell (in macrocell). It follows from the data in the Table 1 that the interac- tion of ascorbic acid (AA) and cysteine (Cys) occurs accord- ing to equations (4–5), which correspond to the mecha- nisms of oxidation of these AOs described in the literature. Figure 4 Dependence of the potential on the logarithm of the K3[Fe(CN)6]/K4[Fe(CN)6] ratio, obtained using a microcell. Scheme 1 Ascorbic acid oxidation scheme. Scheme 2 Pyrogallol oxidation scheme. Scheme 3 Glutathione oxidation scheme. Scheme 4 Cysteine oxidation scheme. https://doi.org/10.15826/chimtech.2023.10.1.04 Chimica Techno Acta 2023, vol. 10(1), No. 202310104 ARTICLE 5 of 8 DOI: 10.15826/chimtech.2023.10.1.04 (4) (5) In case of pyrogallol, rather high values of stoichio- metric coefficients were obtained in the reaction with po- tassium hexacyanoferrate (III). Such values are associated not only with the electron transfer mechanism, but also with the possible mechanism of complex formation with iron ions [34–35] as a result of a competing reaction. It is known that polyphenolic compounds having gallic struc- tures are able to form fairly stable complexes with metals of variable valence and inhibit radical processes at the stage of chain branching (Scheme 5). Thus, the AOС values of the model solutions of antioxi- dants obtained in the microcell are confirmed by the "in- troduced-found" method, taking into account stoichio- metric coefficients, and these values are similar to those obtained in the standard electrochemical cell. The calcu- lated t-test and F-test these values are range from 0.5 to 1.7 and 0.4 to 1.1, respectively, which are significantly be- low the critical values at a 95% confidence level (tkrit = 2.57, Fkrit = 5.05). This shows that the variances of the two populations are homogeneous. The relative stand- ard deviation does not exceed 8%. Since the AOС data obtained using the microсell are quite reproducible and similar to the results obtained in the laboratory cell, the microсell design can be used to determine the content of antioxidants. However, the open design of the microсell is difficult to use on-site. The design of the second model in the form of the micro- fluidic device was developed to eliminate this drawback. Figure 5 shows the scheme of preparation and analysis on the microfluidic device. The scheme of the microfluidic device is shown in Figure 6. For analysis, the purified platinum wire and the silver wire coated with an insoluble silver salt are placed in the electrode holes of the microfluidic device (stage I). The next step is to wash the microfluidic device with water and the solution of the K3[Fe(CN)6]/K4[Fe(CN)6] system (stage II). The systems of potassium hexacyanoferrates (1) and analyte (2) are injected using the syringe pump. In this case, the K3[Fe(CN)6]/K4[Fe(CN)6] system is pumped continuously at a constant flow rate (stage III). The anti- oxidant solution is injected after equilibrium is estab- lished on the platinum electrode (stage IV). The system solution, flowing through the microfluidic channels (3) to the near-electrode space (4), is mixed with the antioxi- dant. Then, the potential change is recorded. All studies were carried out in 0.1 M KCl. The kinetic characteristics, namely, the half-reaction period of the interaction of the antioxidant with K3[Fe(CN)6], for a number of natural antioxidants, which are most often found in food and pharmaceutical objects, were analyzed to select the length and shape of microfluidic channels (Table 2). Table 1 АОC of model solutions of antioxidants (САО=0.1 mmol/dm 3, n = 5, P = 0.95) and their mixtures. Name CAO, 10 –4 mol/dm3 АОC, 10–4 mol-eq/dm3 (in micro- cell) АОC, 10–4 mol-eq/dm3 (in macro- cell) n Ascorbic acid 1 1.83±0.05 1.98±0.02 1.83 Cysteine 1 1.10±0.04 1.01±0.01 1.10 Pyrogallol 1 5.43±0.11 5.17±0.06 5.43 Mixtures of antioxidant solutions Ascorbic acid : Cys- teine 1:1 3.05±0.09 2.94±0.03 2:1 5.01±0.05 4.96±0.06 1:2 4.13±0.17 4.05±0.04 Scheme 5 Scheme of the formation of pyrogallol complexes with iron ions. Figure 5 Scheme of analysis using the microfluidic device. https://doi.org/10.15826/chimtech.2023.10.1.04 Chimica Techno Acta 2023, vol. 10(1), No. 202310104 ARTICLE 6 of 8 DOI: 10.15826/chimtech.2023.10.1.04 Figure 6 The scheme of the microfluidic device. Table 2 Half-reaction periods of the interaction of antioxidants with K3[Fe(CN)6] (САО = 0.1 mmol/dm 3, n = 5, P = 0.95). Name τ1/2, sec RSD (%) Ascorbic acid 3 5 Cysteine 7 5 Pyrogallol 5 3 Caffeic acid 3 5 Rutin 3 5 Quercetin 10 4 Luteolin 4 3 Dihydromyricetin 6 1 Phloroglucinol 133 3 Glutathione 155 6 Catechol 376 5 The optimal reaction time was chosen based on the da- ta in Table 2, which was 10 minutes. The overall dimen- sions of the microfluidic device were 60×30 mm, the channel diameter was d = 1 mm, the channel length was l = 100 mm, the flow rate was V = 50 ml/hour. The antioxidant capacity of some solutions of model antioxidants and their mixtures was determined using the microfluidic device (Table 3). The correctness of the ob- tained results, similarly to the AOC obtained in the micro- cell, was determined by the "introduced-found" method, taking into account stoichiometric coefficients. The data obtained in the microfluidic device and in the standard laboratory electrochemical cell agree with each other (cal- culated t-test and F-test range from 0.3 to 1.5 and 0.2 to 1.3, respectively), and are consistent with the literature data. The relative standard deviation does not exceed 10%. The quantitation limit of AOC by the potentiometric method using the microfluidic device was calculated. The dependence of the calculated values of the relative stand- ard deviation from the average values of AOC at different concentrations of ascorbic acid was plotted to determine the quantitation limit (Figure 7). According to the 3σ crite- rion, it was 5.20·10–6 mol-eq/dm3, which is sufficient for studying objects with a low content of antioxidants. Thus, working range of the developed device was (5.2·10–6– 9.9·10–3) mol-eq/dm3. According to IUPAC, the response time of electrodes is defined as the time required to reach 95% of the equilibri- um potential for each tenfold change in concentration [36]. Table 3 АОC of model solutions of antioxidants (САО = 0.1 mmol/dm 3, n = 5, P = 0.95) and their mixtures. Name CAO, 10 –4 mol/dm3 АОC, 10–4 mol-eq/dm3 (in micro- cell) АОC, 10–4 mol-eq/dm3 (in macro- cell) n Ascorbic acid 1 2.16±0.07 1.98±0.02 2.16 Cysteine 1 1.28±0.06 1.01±0.01 1.28 Glutathione 1 1.22±0.09 0.98±0.01 1.22 Pyrogallol 1 4.48±0.27 5.17±0.06 4.48 Mixtures of antioxidant solutions Ascorbic acid : Cysteine 1:1 3.32±0.17 2.94±0.03 Ascorbic acid : Glutathione 1:1 3.41±0,16 3.12±0.09 Figure 7 Dependence of relative standard deviation on AOC at different concentrations of ascorbic acid. In this study, the response time was investigated in the concentration range of the K3[Fe(CN)6]/K4[Fe(CN)6] system from 0.01 M/0.1 mM to 0.01 M/1 mM. As a result, the response time of the developed device was found to be 60 s. AOC of multicomponent objects, which are mass- produced drinks (Table 4), is determined. The composition of mass-produced drinks includes freshly squeezed juice and pulp of fruits and berries containing polyphenolic compounds, vitamins A, C and E – natural antioxidants [29]. The selected objects of analysis were not subjected to additional sample preparation. Thus, beverages such as Lyubimiy Peach and Dobry Cherry juices, as well as Coca-Cola Lime, did not show antioxidant properties. Perhaps, this is due to the quality and storage conditions of raw materials and finished products. Rich Orange, Sady Pridonya Apple-Cherry, Lyubimiy Multifruit, Dobry Apple-Pear, and Lipton Green Iced Tea exhibit antioxidant properties. The relative standard devi- ation of the AOC results obtained in the microfluidic de- vice did not exceed 10%. The highest content of antioxi- dants was found in Rich Orange juice. The correlation coefficient of the AOC results obtained in the microfluidic device and in the laboratory cell was 0.90 (rkrit = 0.80), which indicates a good convergence of the data and the possibility of using the potentiometric method implemented in the microfluidic device to assess the antioxidant capacity of multicomponent objects. × https://doi.org/10.15826/chimtech.2023.10.1.04 Chimica Techno Acta 2023, vol. 10(1), No. 202310104 ARTICLE 7 of 8 DOI: 10.15826/chimtech.2023.10.1.04 Table 4 АОC of industrial drinks (n = 5, P = 0.95). Name АОC, 10–2 mol- eq/dm3 (in microcell) АОC, 10–2 mol- eq/dm3 (in macrocell) Rich Orange 5.60±0.29 6.20±0.07 Sady Pridonia Apple- Cherry 0.09±0.02 0.19±0.01 Lipton Green Iced Tea 2.14±0.11 2.62±0.04 Lyubimiy Multifruit 3.24±0.94 2.57±0.02 Dobry Apple-Pear 0.43±0.06 0.75±0.04 4. Limitations In this work, the silver wire, coated with an insoluble sil- ver salt, was used as a reference electrode. This electrode is quite common. However, the use of silver wire has some limitations associated with damage to the upper layer of silver chloride during repeated use and the need for its redeposition. In order to increase the capability of using these devices multiple times, it will be necessary to con- duct a study on the choice of material and design of the reference electrode. 5. Conclusions In this work, two prototypes of portable devices were de- veloped – the open microcell and the flow microfluidic device, based on the potentiometric method using the K3[Fe(CN)6]/K4[Fe(CN)6] system. The high reproducibility of the AOC results and the similarity with the data obtained in the standard laboratory electrochemical cell suggest the possibility of using the developed designs of portable devices for the express assessment of the antioxidant content in complex multicomponent objects. Thus, the potentiometric method for determining the antioxidant content, due to the simplicity of hardware de- sign, the possibility of miniaturization of the measurement cell and express analysis, is quite promising from the point of view of implementation in the portable device. Further research will be aimed at improving the design of the prototypes in order to develop the analytical platform for the determination of antioxidants in various objects. ● Supplementary materials No supplementary materials are available. ● Funding The research funding from the Ministry of Science and Higher Education of the Russian Federation (Ural Federal University Program of Development within the Priority- 2030 Program) is gratefully acknowledged. ● Acknowledgments None. ● Author contributions Conceptualization: A.V.I., E.R.S., A.I.M. Data curation: E.R.S., E.L.G. Formal Analysis: E.R.S., D.I.I. Funding acquisition: A.V.I., E.L.G., D.I.I. Investigation: D.S.G., E.A.Y. Methodology: A.V.I., E.R.S., E.L.G. Project administration: E.R.S. Resources: D.S.G., E.A.Y., D.I.I. Software: D.S.G., E.A.Y. Supervision: A.V.I., A.I.M. Validation: A.V.I., E.R.S., E.L.G. Visualization: E.R.S. Writing – original draft: E.R.S. Writing – review & editing: A.V.I., E.R.S., E.L.G. ● Conflict of interest The authors declare no conflict of interest. ● Additional information Author IDs: Elena R. Salimgareeva, Scopus ID 57193423139; Dinara I. Igdisanova, Scopus ID 57364641300; Daria S. Gordeeva, Scopus ID 57212411112; Elena A. Yarkova, Scopus ID 57204419700; Anatoly I. Matern, Scopus ID 12142454900; Elena L. Gerasimova, Scopus ID 8343024000; Alla V. Ivanova, Scopus ID 8233431000. Website: Ural Federal University, https://urfu.ru/en. References 1. Neha K, Haider MR, Pathak A, Yar MS. Medicinal prospects of antioxidants: A review. Eur J Med Chem. 2019;178:687–704. doi:10.1016/j.ejmech.2019.06.010 2. Pisoschi AM, Pop A. The role of antioxidants in the chemistry of oxidative stress: A review. Eur J Med Chem. 2015;97:55– 74. doi:10.1016/j.ejmech.2015.04.040 3. Denisov ET, Afanas’ev IB. Oxidation and antioxidants in or- ganic chemistry and biology. United Kingdom: Taylor & Fran- cis Group; 2005. 992 p. 4. Apak R, Gorinstein S, Böhm V, Schaich KM, Özyürek M, Güçlü K. Methods of measurement and evaluation of natural antiox- idant capacity/activity (IUPAC Technical report). Pure Appl Chem. 2013:85(5):957–998. doi:10.1351/PAC-REP-12-07-15 5. Arts M JT J, Dallinga JS, Voss H-P, Haenen GRMM, Bast A. A critical appraisal of the use of the antioxidant capacity (TEAC) assay in defining optimal antioxidant structures. Food Chem. 2003;80(3):409–414. doi:10.1016/С0308-8146(02)00468-5 6. Van Den Berg R, Haenen GRMM, Van Den Berg H, Bast A. Applicability of an improved Trolox equivalent antioxidant capacity (TEAC) assay for evaluation of antioxidant capacity measurements of mixtures. Food Chem. 1999;66(4):511–517. doi:10.1016/S0308-8146(99)00089-8 7. Wayner DDM, Burton GW, Ingold KU, Barclay LRC, Locke SJ. The relative contributions of vitamin E, urate, ascorbate and proteins to the total peroxyl radical-trapping antioxidant ac- https://doi.org/10.15826/chimtech.2023.10.1.04 https://www.scopus.com/authid/detail.uri?authorId=57193423139 https://www.scopus.com/authid/detail.uri?authorId=57364641300&origin=recordPage https://www.scopus.com/authid/detail.uri?authorId=57212411112 https://www.scopus.com/authid/detail.uri?authorId=57204419700 https://www.scopus.com/authid/detail.uri?authorId=12142454900 https://www.scopus.com/authid/detail.uri?authorId=8343024000 https://www.scopus.com/authid/detail.uri?authorId=8233431000 https://urfu.ru/en https://doi.org/10.1016/j.ejmech.2019.06.010 https://doi.org/10.1016/j.ejmech.2015.04.040 https://doi.org/10.1351/PAC-REP-12-07-15 https://doi.org/10.1016/С0308-8146(02)00468-5 https://doi.org/10.1016/S0308-8146(99)00089-8 Chimica Techno Acta 2023, vol. 10(1), No. 202310104 ARTICLE 8 of 8 DOI: 10.15826/chimtech.2023.10.1.04 tivity of human blood plasma. Biochim Biophys Acta 1987;924(3):408–419. doi:10.1016/0304-4165(87)90155-3 8. Wayner DDM. Radical-trapping antioxidants in vitro and in vivo. Bioelectrochem Bioenerg. 1987;18(1–3):219–229. doi:10.1016/0302-4598(87)85024-9 9. Huang D, Ou B, Hampsch-Woodill M, Flanagan JA, Deemer EK. Development and Validation of Oxygen Radical Absorb- ance Capacity Assay for Lipophilic Antioxidants Using Ran- domly Methylated β-Cyclodextrin as the Solubility Enhancer. J Agric Food Chem. 2002;50(7):1815–1821. doi:10.1021/jf0113732 10. Benzie IFF, Strain JJ. The ferric reducing ability of plasma (FRAP) as a measure of ‘‘Antioxidant Power’’: the FRAP assay. Anal Biochem. 1996;239:70‒76. doi:10.1006/abio.1996.0292 11. Apak R, Güçlü K, Demirata B, Özyürek M, Çelik SE, Bektaşoğlu B, Berker KI, Özyurt D. Comparative evaluation of various total antioxidant capacity assays applied to phenolic compounds with the CUPRAC assay. Molec. 2007;12:1496‒ 1547. doi:10.3390/12071496 12. Benera M, Apak R. Ferric-o-phenanthroline adsorbed on a Nafion membrane: A novel optical sensor for antioxidant ca- pacity measurement of food extracts. Sens Actuators B Chem. 2017;247:155–162. doi:10.1016/j.snb.2017.03.017 13. Bener M, Ozyurek M, Guclu K, Apak R. Development of a low- cost optical sensor for cupric reducing antioxidant capacity measurement of food extracts. Anal Chem. 2010;82:4252– 4258. doi:10.1021/ac100646k 14. Apak R, Guclu K, Ozyurek M, Karademir S.E. Novel Total An- tioxidant Capacity Index for Dietary Polyphenols and Vita- mins C and E, Using Their Cupric Ion Reducing Capability in the Presence of Neocuproine: CUPRAC Method. J Agric Food Chem. 2004;52:7970−7981. doi:10.1021/jf048741x 15. Sharpe E, Frasco T, Andreescu D, Andreescu S. Portable ceria nanoparticle-based assay for rapid detection of food antioxi- dants (NanoCerac). Anal. 2013;138:249–262. doi:10.1039/c2an36205h 16. Arikana B, Alpa FN, Ozfidan-Konakcib C, Balcia M, Elbasana F, Yildiztugaya E, Cavusoglu H. Fe2O3-modified graphene ox- ide mitigates nanoplastic toxicity via regulating gas ex- change, photosynthesis, and antioxidant system in Triticum aestivum. Chemosphere. 2022;307(4):136048. doi:10.1016/j.chemosphere.2022.136048 17. Zhanga S, Chena J, Lianb M-L, Yanga W-Sh, Chena X. An en- gineered, self-propelled nanozyme as reactive oxygen species scavenger. Chem Engineer J. 2022;446(2):136794. doi:10.1016/j.cej.2022.136794 18. Ivanova A, Gerasimova E, Gazizullina E, Borisova M, Drokin R, Gorbunov E, Ulomskiy E, Rusinov V. The antioxidant screening of potential materials for drugs based on 6-nitro- 1,2,4-triazoloazines containing natural polyphenol fragments. Anal Bioanal Chem. 2020;412:5147–5155. doi:10.1007/s00216-020-02466-2 19. Ivanova A, Gerasimova E, Gazizullina E. Study of antioxidant properties of agents from the perspective of their action mechanisms. Molec. 2020;25:4251. doi:10.3390/molecules25184251 20. Özbeka O, Berkel C. Recent advances in potentiometric analy- sis: Paper–based devices. Sens Intern. 2022;3:100189. doi:10.1016/j.sintl.2022.100189 21. Özbek O, Isildak Ö. Potentiometric determination of cop- per(II) ions based on a porphyrin derivative. J Chin Chem Soc. 2022;69(7):1060–1069. doi:10.1002/jccs.202200168 22. Özbek O, Isildak Ö. Potentiometric PVC membrane sensor for the determination of anti-epileptic drug levetiracetam in Pharmaceutical formulations. Chem Sel. 2022;7(3):1–8. doi:10.1002/slct.202103988 23. Özbek O, Isildak Ö. Use of 5,10,15,20-tetrakis(p- chlorophenyl)porphyrin as sensor material: potentiometric determination of aluminium(III) ions. Bull Mater Sci. 2022;45(114):1–10. doi:10.1007/s12034-022-02696-3 24. Ivanova AV, Gerasimova EL, Brainina KhZ. Potentiometric Study of Antioxidant Activity: Development and Prospects. Crit Rev Anal Chem. 2015;45:311–322. doi:10.1080/10408347.2014.910443 25. Ivanova AV, Gerasimova EL, Gazizullina ER. An integrated approach to the investigation of antioxidant properties by po- tentiometry. Anal Chim Acta. 2020;111:83–91. doi:10.1016/j.aca.2020.03.041 26. Eksperiandova LP, Belikov KN, Khimchenko SV, Blank TA. Once again about determination and detection limits. J Anal Chem. 2010;65(3):223–228. doi:10.1134/S1061934810030020 27. Shpigun LK, Arharova MA, Brainina KhZ, Ivanova AV. Flow injection potentiometric determination of total antioxidant activity of plant extracts. Anal Chim Acta. 2006;573(574):419–426. doi:10.1016/j.aca.2006.03.094 28. Brainina KhZ, Alyoshina LV, Gerasimova EL, Kazakov YaE, Beykin YaB, Belyaeva SV, Usatova TI, Inzhevatova OV, Ivano- va AV, Khodos MY. New electrochemical methods of deter- mining antioxidant activity of blood and blood fractions. Electroanal. 2009;21:618–624. doi:10.1002/elan.200804458 29. Menshchikov EB, Lankin VZ, Kandalintseva NV. Phenolic an- tioxidants in biology and medicine. Structures, properties, mechanisms of action. Germany: LAP LAMBERT Academic Publishing; 2012. 488 p. 30. Padayatty SJ, Katz A, Wang Ya, Eck P, Kwon O, Lee Je-H, Chen Sh, Corpe Ch, Dutta A, Dutta SK, Levine M. Vitamin C as an an- tioxidant: evaluation of its role in disease prevention. J Am Coll Nutr. 2003;22(1):18−35. doi:10.1080/07315724.2003.10719272 31. Bensalah N, Trabelsi H, Gadri A. Electrochemical treatment of aqueous wastes containing pyrogallol by BDD-anodic oxi- dation. J Environ Manage. 2009;90:523–530. doi:10.1016/j.jenvman.2007.12.007 32. Zinatullina KM, Kasaikina OT, Kuzmin VA, Khrameeva NP. Pro- and antioxidant characteristics of natural thiols. Rus Chem Bull. 2018;67(4):726‒730. doi:10.1007/s11172-018-2129-0 33. Anderson ME. Glutathione and glutathione delivery com- pounds. Adv Pharmacol. 1996;38:65‒78. doi:10.1016/S1054-3589(08)60979-5 34. Perron NR, Brumaghim JL. A review of the antioxidant mech- anisms of polyphenol compounds related to iron binding. Cell Biochem Biophys. 2009;53:75–100. doi:10.1007/s12013-009-9043-х 35. Ivanova A, Gerasimova E, Gazizullina E. Study of antioxidant properties of agents from the perspective of their action mechanisms. Molec. 2020;25:4251. doi:10.3390/molecules25184251 36. Buck R P, Lindner E. Recommendations for nomenclature of ionselective electrodes (IUPAC Recommendations 1994). Pure Appl Chem. 1994;66(12):2527–2536. doi:10.1351/pac199466122527 https://doi.org/10.15826/chimtech.2023.10.1.04 https://doi.org/10.1016/0304-4165(87)90155-3 https://doi.org/10.1016/0302-4598(87)85024-9 https://doi.org/10.1021/jf0113732 https://doi.org/10.1006/abio.1996.0292 https://doi.org/10.3390/12071496 https://doi.org/10.1016/j.snb.2017.03.017 https://doi.org/10.1021/ac100646k https://doi.org/10.1021/jf048741x https://doi.org/10.1039/c2an36205h https://doi.org/10.1016/j.chemosphere.2022.136048 https://doi.org/10.1016/j.cej.2022.136794 https://doi.org/10.1007/s00216-020-02466-2 https://doi.org/10.3390/molecules25184251 https://doi.org/10.1016/j.sintl.2022.100189 https://doi.org/10.1002/jccs.202200168 https://doi.org/10.1002/slct.202103988 https://doi.org/10.1007/s12034-022-02696-3 https://doi.org/10.1080/10408347.2014.910443 https://doi.org/10.1016/j.aca.2020.03.041 https://doi.org/10.1134/S1061934810030020 https://doi.org/10.1016/j.aca.2006.03.094 https://doi.org/10.1002/elan.200804458 https://doi.org/10.1080/07315724.2003.10719272 https://doi.org/10.1016/j.jenvman.2007.12.007 https://doi.org/10.1007/s11172-018-2129-0 https://doi.org/10.1016/S1054-3589(08)60979-5 https://doi.org/10.1007/s12013-009-9043-х https://doi.org/10.3390/molecules25184251 https://doi.org/10.1351/pac199466122527