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12 pages, 1935 KiB

Open AccessFeature PaperArticle

Simultaneous Detection of Ammonium and Nitrate in Environmental Samples Using on Ion-Selective Electrode and Comparison with Portable Colorimetric Assays

by Jittima Choosang, Apon Numnuam, Panote Thavarungkul, Proespichaya Kanatharana, Tanja Radu, Sami Ullah and Aleksandar Radu

Sensors 2018, 18(10), 3555; https://0-doi-org.brum.beds.ac.uk/10.3390/s18103555 - 19 Oct 2018

Cited by 35 | Viewed by 6472

Abstract

Simple, robust, and low-cost nitrate- and ammonium-selective electrodes were made using substrate prepared from household materials. We explored phosphonium-based ILs and poly (methyl methacrylate)/poly(decyl methacrylate)(MMA-DMA) copolymer as matrix materials alternative to classical PVC-based membranes. IL-based membranes showed suitability only for nitrate-selective electrode exhibiting [...] Read more.

Simple, robust, and low-cost nitrate- and ammonium-selective electrodes were made using substrate prepared from household materials. We explored phosphonium-based ILs and poly (methyl methacrylate)/poly(decyl methacrylate)(MMA-DMA) copolymer as matrix materials alternative to classical PVC-based membranes. IL-based membranes showed suitability only for nitrate-selective electrode exhibiting linear concentration range between 5.0 × 10⁻⁶ and 2.5 × 10⁻³ M with a detection limit of 5.5 × 10⁻⁷ M. On the other hand, MMA-DMA—based membranes showed suitability for both ammonium- and nitrate-selective electrodes, and were successfully applied to detect NO₃⁻ and NH₄⁺ in water and soil samples. The proposed ISEs exhibited near-Nernstian potentiometric responses to NO₃⁻ and NH₄⁺ with the linear range concentration between 5.0 × 10⁻⁵ and 5.0 × 10⁻² M (LOD = 11.3 µM) and 5.0 × 10⁻⁶ and 1.0 × 10⁻³ M (LOD = 1.2 µM), respectively. The power of ISEs to detect NO₃⁻ and NH₄⁺ in water and soils was tested by comparison with traditional, portable colorimetric techniques. Procedures required for analysis by each technique from the perspective of a non-trained person (e.g., farmer) and the convenience of the use on the field are compared and contrasted. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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11 pages, 2846 KiB

Open AccessFeature PaperArticle

Ruthenium Oxide Nanorods as Potentiometric pH Sensor for Organs-On-Chip Purposes

by Esther Tanumihardja, Wouter Olthuis and Albert Van den Berg

Sensors 2018, 18(9), 2901; https://0-doi-org.brum.beds.ac.uk/10.3390/s18092901 - 01 Sep 2018

Cited by 22 | Viewed by 6471

Abstract

A ruthenium oxide (RuOx) sensor for potentiometric pH sensing is currently being developed for organs-on-chip purposes. The sensor was fabricated from a Ru(OH)₃ precursor, resulting in RuOx nanorods after heating. An open-circuit potential of the RuOx electrode showed a near-Nernstian response of [...] Read more.

A ruthenium oxide (RuOx) sensor for potentiometric pH sensing is currently being developed for organs-on-chip purposes. The sensor was fabricated from a Ru(OH)₃ precursor, resulting in RuOx nanorods after heating. An open-circuit potential of the RuOx electrode showed a near-Nernstian response of −58.05 mV/pH, with good selectivity against potentially interfering ions (lithium, sulfate, chloride, and calcium ions). The preconditioned electrode (stored in liquid) had a long-term drift of −0.8 mV/h, and its response rate was less than 2 s. Sensitivity to oxygen was observed at an order of magnitude lower than other reported metal-oxide pH sensors. Together with miniaturizability, the RuOx pH sensor proves to be a suitable pH sensor for organs-on-chip studies. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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12 pages, 2464 KiB

Open AccessArticle

Electronic Tongue for Brand Uniformity Control: A Case Study of Apulian Red Wines Recognition and Defects Evaluation ^†

by Larisa Lvova, Irina Yaroshenko, Dmitry Kirsanov, Corrado Di Natale, Roberto Paolesse and Andrey Legin

Sensors 2018, 18(8), 2584; https://0-doi-org.brum.beds.ac.uk/10.3390/s18082584 - 07 Aug 2018

Cited by 21 | Viewed by 3659

Abstract

The potentiometric electronic tongue system has been tested as a potential analytical tool for brand uniformity control of monoculture Apulian red wines (Primitivo and Negroamaro). The sensor array was composed of eight porphyrin coatings obtained by electrochemical polymerization process and was employed for [...] Read more.

The potentiometric electronic tongue system has been tested as a potential analytical tool for brand uniformity control of monoculture Apulian red wines (Primitivo and Negroamaro). The sensor array was composed of eight porphyrin coatings obtained by electrochemical polymerization process and was employed for both wines discrimination and quantitative detection of wine defect compounds: “off-odour” 3-(methylthio)-propanol; isoamyl alcohol fusel oil; benzaldehyde (marker of the yeast activity) and acetic acid (marker of vinegar formation). PLS-DA applied to Electronic tongue output data has permitted a correct discrimination of more than 70% of analysed wines in respect to the original brand affiliation. Satisfactory PLS1 predictions were obtained in real wine samples; with R² = 0.989 for isoamyl alcohol and R² = 0.732 for acetic acid. Moreover; the possibility to distinguish wine samples on the base of permitted levels of fault compounds content was shown. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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15 pages, 3182 KiB

Open AccessArticle

Cheeses Made from Raw and Pasteurized Cow’s Milk Analysed by an Electronic Nose and an Electronic Tongue

by Nuno I. P. Valente, Alisa Rudnitskaya, João A. B. P. Oliveira, Elvira M. M. Gaspar and M. Teresa S. R. Gomes

Sensors 2018, 18(8), 2415; https://0-doi-org.brum.beds.ac.uk/10.3390/s18082415 - 25 Jul 2018

Cited by 25 | Viewed by 4857

Abstract

Cheese prepared from whole milk, raw and pasteurized, were analysed by an electronic nose based on piezoelectric quartz crystals and an electronic tongue based on potentiometric sensors, immediately after their preparation and along ripening (after 7 and 21 days). Whey was also analysed [...] Read more.

Cheese prepared from whole milk, raw and pasteurized, were analysed by an electronic nose based on piezoelectric quartz crystals and an electronic tongue based on potentiometric sensors, immediately after their preparation and along ripening (after 7 and 21 days). Whey was also analysed by the potentiometric electronic tongue. Results obtained by the electronic nose and tongue were found to be complementary, with the electronic nose being more sensitive to differences in the milk and the electronic tongue being more sensitive to milk pasteurization. Electronic tongue was able to distinguish cheeses made from raw and pasteurized milk, both analysing the whey or the curd, with correct classification rate of 96% and 84%, respectively. Besides, the electronic nose was more sensitive than the electronic tongue to the ripening process, with large differences between samples after 7 and 21 days, while the electronic tongue was only sensitive to the initial maturation stages, with large difference between freshly prepared cheese and with seven days of maturation. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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18 pages, 3986 KiB

Open AccessArticle

Potentiometric Sensors for Iodide and Bromide Based on Pt(II)-Porphyrin

by Dana Vlascici, Nicoleta Plesu, Gheorghe Fagadar-Cosma, Anca Lascu, Mihaela Petric, Manuela Crisan, Anca Belean and Eugenia Fagadar-Cosma

Sensors 2018, 18(7), 2297; https://0-doi-org.brum.beds.ac.uk/10.3390/s18072297 - 16 Jul 2018

Cited by 28 | Viewed by 4220

Abstract

Pt(II) 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin (PtTMeOPP) was used in the construction of new ion-selective sensors. The potentiometric response characteristics (slope and selectivity) of iodide and bromide-selective electrodes based on (PtTMeOPP) metalloporphyrin in o-nitrophenyloctylether (NPOE), dioctylphtalate (DOP) and dioctylsebacate (DOS) plasticized poly(vinyl chloride) membranes are compared. [...] Read more.

Pt(II) 5,10,15,20-tetra(4-methoxy-phenyl)-porphyrin (PtTMeOPP) was used in the construction of new ion-selective sensors. The potentiometric response characteristics (slope and selectivity) of iodide and bromide-selective electrodes based on (PtTMeOPP) metalloporphyrin in o-nitrophenyloctylether (NPOE), dioctylphtalate (DOP) and dioctylsebacate (DOS) plasticized poly(vinyl chloride) membranes are compared. The best results were obtained for the membranes plasticized with DOP and NPOE. The sensors have linear responses with near-Nernstian slopes toward bromide and iodide ions and good selectivity. The membrane plasticized with NPOE was electrochemically characterized using the EIS method to determine its water absorption and the diffusion coefficient into the membrane. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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10 pages, 1630 KiB

Open AccessFeature PaperArticle

Electrochemical Properties of Nitrate-Selective Electrodes: The Dependence of Resistance on the Solution Concentration

by Arina Ivanova and Konstantin Mikhelson

Sensors 2018, 18(7), 2062; https://0-doi-org.brum.beds.ac.uk/10.3390/s18072062 - 28 Jun 2018

Cited by 20 | Viewed by 4296

Abstract

The electrochemical properties of ion-exchanger-based solvent polymeric ion-selective electrodes (ISEs)—bulk and interfacial resistance, capacitance, and polarization under a galvanostatic current step—are studied, with a nitrate ISE based on tetradecylammonium nitrate (TDANO₃) as a model system. The study is performed by chronopotentiometric [...] Read more.

The electrochemical properties of ion-exchanger-based solvent polymeric ion-selective electrodes (ISEs)—bulk and interfacial resistance, capacitance, and polarization under a galvanostatic current step—are studied, with a nitrate ISE based on tetradecylammonium nitrate (TDANO₃) as a model system. The study is performed by chronopotentiometric and impedance measurements, and focuses on the dependence of the aforementioned properties on the concentration of NO₃⁻ anions in solution. The impacts from the bulk and the interfacial charge transfer to the overall membrane resistance are revealed. It is shown that the bulk resistance of the membranes decreases over an increase of NO₃⁻ concentration within the range of a Nernstian potentiometric response of the ISE. This fact, also reported earlier for K⁺- and Ca²⁺-selective ISEs, is not in line with current views of the mechanism of the ISE response, or of the role of ion exchange in particular. The origin of this effect is unclear. Estimates are made for the concentration of ionized species (NO₃⁻ and TDA⁺) and, respectively, for the TDANO₃ association constant, as well as for the species diffusion coefficients in the membrane. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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11 pages, 5242 KiB

Open AccessArticle

High Sensitive pH Sensor Based on AlInN/GaN Heterostructure Transistor

by Yan Dong, Dong-Hyeok Son, Quan Dai, Jun-Hyeok Lee, Chul-Ho Won, Jeong-Gil Kim, Dunjun Chen, Jung-Hee Lee, Hai Lu, Rong Zhang and Youdou Zheng

Sensors 2018, 18(5), 1314; https://0-doi-org.brum.beds.ac.uk/10.3390/s18051314 - 24 Apr 2018

Cited by 13 | Viewed by 5361

Abstract

The AlInN/GaN high-electron-mobility-transistor (HEMT) indicates better performances compared with the traditional AlGaN/GaN HEMTs. The present work investigated the pH sensor functionality of an analogous HEMT AlInN/GaN device with an open gate. It was shown that the Al_0.83In_0.17N/GaN device demonstrates [...] Read more.

The AlInN/GaN high-electron-mobility-transistor (HEMT) indicates better performances compared with the traditional AlGaN/GaN HEMTs. The present work investigated the pH sensor functionality of an analogous HEMT AlInN/GaN device with an open gate. It was shown that the Al_0.83In_0.17N/GaN device demonstrates excellent pH sense functionality in aqueous solutions, exhibiting higher sensitivity (−30.83 μA/pH for AlInN/GaN and −4.6 μA/pH for AlGaN/GaN) and a faster response time, lower degradation and good stability with respect to the AlGaN/GaN device, which is attributed to higher two-dimensional electron gas (2DEG) density and a thinner barrier layer in Al_0.83In_0.17N/GaN owning to lattice matching. On the other hand, the open gate geometry was found to affect the pH sensitivity obviously. Properly increasing the width and shortening the length of the open gate area could enhance the sensitivity. However, when the open gate width is too larger or too small, the pH sensitivity would be suppressed conversely. Designing an optimal ratio of the width to the length is important for achieving high sensitivity. This work suggests that the AlInN/GaN-based 2DEG carrier modulated devices would be good candidates for high-performance pH sensors and other related applications. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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12 pages, 1742 KiB

Open AccessArticle

Investigation of Sensitivities and Drift Effects of the Arrayed Flexible Chloride Sensor Based on RuO₂/GO at Different Temperatures

by Shi-Chang Tseng, Tong-Yu Wu, Jung-Chuan Chou, Yi-Hung Liao, Chih-Hsien Lai, Siao-Jie Yan and Ting-Wei Tseng

Sensors 2018, 18(2), 632; https://0-doi-org.brum.beds.ac.uk/10.3390/s18020632 - 20 Feb 2018

Cited by 15 | Viewed by 3470

Abstract

We investigate the temperature effect on sensing characteristics and drift effect of an arrayed flexible ruthenium dioxide (RuO₂)/graphene oxide (GO) chloride sensor at different solution temperatures between 10 °C and 50 °C. The average sensor sensitivities according to our experimental results [...] Read more.

We investigate the temperature effect on sensing characteristics and drift effect of an arrayed flexible ruthenium dioxide (RuO₂)/graphene oxide (GO) chloride sensor at different solution temperatures between 10 °C and 50 °C. The average sensor sensitivities according to our experimental results were 28.2 ± 1.4 mV/pCl (10 °C), 42.5 ± 2.0 mV/pCl (20 °C), 47.1 ± 1.8 mV/pCl (30 °C), 54.1 ± 2.01 mV/pCl (40 °C) and 46.6 ± 2.1 mV/pCl (50 °C). We found the drift effects of an arrayed flexible RuO₂/GO chloride sensor in a 1 M NaCl solution to be between 8.2 mV/h and 2.5 mV/h with solution temperatures from 10 °C to 50 °C. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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21 pages, 741 KiB

Open AccessTechnical Note

Measurement Uncertainty Calculations for pH Value Obtained by an Ion-Selective Electrode

by Józef Wiora and Alicja Wiora

Sensors 2018, 18(6), 1915; https://0-doi-org.brum.beds.ac.uk/10.3390/s18061915 - 12 Jun 2018

Cited by 8 | Viewed by 5594

Abstract

An assessment of measurement uncertainty is a task, which has to be the final step of every chemical assay. Apart from a commonly applied typical assessment method, Monte Carlo (MC) simulations may be used. The simulations are frequently performed by a computer program, [...] Read more.

An assessment of measurement uncertainty is a task, which has to be the final step of every chemical assay. Apart from a commonly applied typical assessment method, Monte Carlo (MC) simulations may be used. The simulations are frequently performed by a computer program, which has to be written, and therefore some programming skills are required. It is also possible to use a commonly known spreadsheet and perform such simulations without writing any code. Commercial programs dedicated for the purpose are also available. In order to show the advantages and disadvantages of the ways of uncertainty evaluation, i.e., the typical method, the MC method implemented in a program and in a spreadsheet, and commercial programs, a case of pH measurement after two-point calibration is considered in this article. The ways differ in the required mathematical transformations, degrees of software usage, the time spent for the uncertainty calculations, and cost of software. Since analysts may have different mathematical and coding skills and practice, it is impossible to point out the best way of uncertainty assessment—all of them are just as good and give comparable assessments. Full article

(This article belongs to the Special Issue Potentiometric Chemical Sensors)

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