A new type of potentiometric solid-state ion-selective electrode (SS-ISE) has been fabricated with an intermediate layer made of 7,7,8,8-tetracyanoquinodimethane (TCNQ) or its ion-radical salts and an ionophore-based ion-selective membrane. To show the influence of the TCNQ layer on electrode selectivity, sodium- and potassium-sensitive membranes were applied. A good Nernstian response with a slope of 59.24 mV/dec in the range from 10(-6.5) to 10(-1) M KCl and 58.68 mV/dec (10(-6) to 10(-1) M NaCl) was observed. The influence of an interfacial water film was assessed by an aqueous-layer test performed during potentiometric measurements. The stability of the electrical potential of the new solid-contact electrodes was tested by performing current-reversal chronopotentiometry, and the capacitance of the electrodes is 132 μF or 154 μF for K(+) and Na(+) solid-contact electrodes. These properties confirmed the analytical applicability of TCNQ-based SC-ISEs and should allow the development of a new solid-state ion sensor group.
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 ...
Nowadays, organic donor-acceptor molecules have attracted a lot of scientific attention because of their unique properties and potential applications in various fields. Although tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) is well known charge transfer salt for a long time, the first application of this material as ion-to-electron transducer in ion-selective electrodes is presented. As a proof of concept, potassium-selective and nitrate-selective solid-state electrodes were constructed. Moreover, TTF-TCNQ intermediate layers were fabricated using two organic solvents. Developed potassium sensors displayed a good Nernstian response with a slope of 58.52 mV/decade (10 −6 -10 −1 M K + ), whereas the nitrate-selective electrodes showed a sensitivity of −58.47 mV/decade (10 −5 -10 −1 M NO − 3 ). Reproducible standard potentials and low detection limits were observed. Potential stability of studied electrodes was evaluated using current-reversal chronopotentiometry. The capacitance of TTF-TCNQ-contacted electrodes is 255 μF and 629 μF for K + and NO − 3 sensors. The results of measurements conducted reveal that TTF-TCNQ has an appropriate effect on potentiometric sensors performance.
This work demonstrates the application of conductive organic crystals (7,7,8,8-tetracyanoquinodimethane (TCNQ) and its sodium salt (NaTCNQ)) supported on carbon nanomaterials (CNMs) as solid contact layer in all-solid-state ion-selective electrodes (ASS-ISEs). As ion-to-electron transductor between the ionically conducting membrane and the electronically conducting glassy carbon new layers based on a high capacity of charge transfer and a redox TCNQ/TCNQ− reaction are proposed. Developed CNM–NaTCNQ–TCNQ-contacted sensors provided a near to Nernstian response to sodium and excellent electrical parameters. The highest electrode capacitance was 2.15 mF, as the potential drift (and electrodes resistance) are significantly reduced due to the presence in solid contact combination of materials having ionic or electron conductivity. Moreover, the introduction of NaTCNQ in sodium-selective electrodes improves their selectivity toward to interfering cations. Carbon nanomaterials type used in the interlayer affects, in the different way, the analytical and electrical parameters of proposed ASS-ISEs. The possibility of improving the electrodes sensitivity, linear range and detection limit, by changing the NaTCQ:TCNQ ratio, is also presented.
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