Improved Nitrate Sensing Using Solid Contact Ion Selective Electrodes Based on TTF and Its Radical Salt

Abstract

The possibility of improving the selectivity of solid-state nitrate-selective electrodes by the application of the tetrathiafulvalene (TTF) or its nitrate salt (TTF(NO 3 )) as an intermediate layer between an electrical conductor and a polymeric membrane is demonstrated. The analytical performance of electrodes was investigated during potentiometric measurements. Fabricated sensors displayed a Nernstian slope (−58.85 mV/decade in the range from 10 −5.0 to 10 −1 M and −59.36 mV/decade in the range from 10 −6.0 to 10 −1 M for TTF− and TTF(NO 3 )−modified electrodes respectively), repeatable and reproducible standard potential and detection limit of 2.5 μM (0.16 mgL −1 ) and 0.63 μM (0.039 mgL −1 ) for TTF− and TTF(NO 3 )−based electrodes, respectively. The selectivity was considerably improved compared to a coated disc electrode or electrodes with intermediate layer based on carbon nanomaterials. Electrical parameters of the proposed sensors were tested by carried out current-reversal chronopotentiometry. In the case of electrodes with the use of TTF or TTF(NO 3 ) the potential drift decreases to 167 μVs −1 or 16.6 μVs −1 and the capacitance is 5.99 μF or 60.3 μF. The proposed sensors were successfully applied in analyzing nitrate concentration in water samples.Nitrates are widely used in the fabrication of fertilizers, drugs, explosives and many products, which significantly contributes to their high concentration in the sewage. 1 The contamination of surface and ground water by nitrate ions is a material problem around the world and their removal is important for two main reasons. This type of water pollution disturbs ecological balance and causes hazard to people health. Nitrates are a source of nitrogen for microbial protein synthesizing, nevertheless excess amount of these ions causes eutrophication in water bodies manifested through uncontrolled growth of algae.The natural level of nitrate in surface water is typically less than 1 mgL −1 due to dilution of surface runoff, plant uptake and denitrification processes. However nitrate pollution has generally increased over time as a result of intensive use of nitrogen fertilizers in agriculture. The maximum acceptable concentration for nitrate has been established at 10 mgL −1 , to be protective of the health. 2,3 Drinking water containing a high concentration of nitrates induces cancer or other health problems, such as the 'blue baby syndrome' in infants. 4 Therefore, it has been necessary to introduce selective, simple and reliable method that could be used for the monitoring the concentrations of nitrates.Several analytical methods for the nitrate determination have been reported including spectrophotometry with the detection limit of 0.031 mgL −1 and 40 μgL −1 , 5,6 chromatography with the detection limit of 0.001 mgL −1 and 0.01 mgL −1 , 7,8 capillary electrophoresis with the detection limit of 0.099 mgL −1 , 9 amperometry with the detection limit of 6.2 ngL −1 , 10 polarography 11 and voltammetry with the detection limit of 5.4 mgL −1 . 12 However, most of ...

Improved Solid-Contact Nitrate Ion Selective Electrodes Based on Multi-Walled Carbon Nanotubes (MWCNTs) as an Ion-to-Electron Transducer

“…Contamination of water resources with nitrate causes disturbances in the ecological balance which is a hazard to human health. In addition, high nitrate levels cause eutrophication in water bodies, which is manifested through uncontrolled growth of algae [2]. Nitrate can be found naturally in surface water at a level <1 mg/L, but this level is greatly disturbed as a result of the intensive use of fertilizers.…”

“…These compounds have attracted a lot of attention due to their unique mechanical, chemical and electrical properties [31], and also have a wide range of applications as an intermediate layer in solid-contact ion-selective electrodes (SC-ISEs); these compounds include graphene, carbon nanotubes, fullrene or carbon black [28,32]. Alhough the usage of nanomaterials improves the analytical parameters of sensors (the potential stability and capacity and the reduction of the resistance of electrodes), they only have a slight effect on the selectivity of the electrodes, which is still comparable to coated-disc electrodes [2].…”

Solid-Contact Ion-Selective Electrodes: Response Mechanisms, Transducer Materials and Wearable Sensors

“…Other Co complexes were reported for the SC, which further demonstrated the redox-buffer stabilized concept [65][66][67][68]. In addition to Co complexes, tetrathiafulvalene (TTF) and its radical salts have also constituted the redox buffers for SC-ISEs [69]. Schuhmann and coworkers presented an intercalative compound (LiFePO 4 /FePO 4 ) [70] redox buffer for ion-to-electron transduction ( Figure 7B,C).…”

Ion-to-electron capacitance of single-walled carbon nanotube layers before and after ion-selective membrane deposition

“…Historically, the need to miniaturize potentiometric sensors gave rise to the development of SC-ISEs and triggered the search for ideal transducer materials. Different transducer materials were described and tested over the years, such as conductive polymers [1][2][3], nano-and microstructured carbonbased materials [4][5][6][7][8][9], redox active compounds and mixtures [10][11][12][13][14][15], as well as several metal-based nanomaterials and composites [16][17][18][19].…”