Nitrate-selective Electrode Research Articles

Potentiometric Sensors with Carbon Black Supporting Platinum Nanoparticles

For the first time, a single-piece, all-solid-state ion-selective electrode was fabricated with carbon black supporting platinum nanoparticles (PtNPs-CB) and a polymeric membrane. The PtNPs-CB, as an intermediate layer, was drop-casted directly on the solid substrate, and then an ionophore-doped solvent polymeric membrane was added in order to form a sensor. The performance of the newly developed electrodes was evaluated on the basis of potassium and nitrate ions. The stability of the electrical potential for the electrodes was examined by performing current-reversal chronopotentiometry, and the influence of the interfacial water film was assessed by the potentiometric aqueous-layer test. Fabricated potassium- and nitrate-selective electrodes displayed a Nernstian slope and several outstanding properties such as high long-term potential stability, potential repeatability, and reproducibility.

Assessing the Potential for Ion Selective Electrodes and Dual Wavelength UV Spectroscopy as a Rapid on-Farm Measurement of Soil Nitrate Concentration

Current fertiliser recommendations for nitrogen are limited in their accuracy and may be improved by the use of simple on-farm soil rapid tests. This paper investigates the potential for using nitrate (NO3−) ion selective electrodes (ISEs) and dual wavelength UV spectroscopy as part of a rapid soil NO3− diagnostic test. Three soil types, representing the major soil types for agriculture in the western UK, were tested. For the three soils, the ISE rapid test procedure gave a near 1:1 response (r2 = 0.978, 0.968, 0.989) compared to the internationally-approved standard laboratory method. However, the accuracy of the ISE rapid test was reduced at low soil NO3− concentrations (<10 mg NO3− L−1). We also show that NO3− analysis of H2O soil extracts by dual wavelength UV spectroscopy was also highly correlated (r2 = 0.978, 0.983, 0.991) to the standard laboratory method. We conclude that both ISE and dual wavelength UV spectroscopy have clear potential to be used for the rapid on-farm determination of soil NO3− concentration. Barriers to use of these field-based assessment tools include, farmer perception of cost-benefit, general attitude to new technologies and the ability to generate useful fertiliser use strategies from soil NO3− measurements.

Thermodynamic study of electrolyte mixture (KCl + KNO3 + water + proline) by potentiometric measurements at T = 298.2 and 303.2 K

In this work, the thermodynamic properties of the mixed electrolyte system (KCl+KNO3+water+proline), using the potentiometric method, are reported. The potentiometric measurements were performed on the galvanic cells without liquid junction of the type: Ag–AgCl|KCl (m1), KNO3 (m2), (100-wt%) H2O+wt% proline|K-ISE, NO3-ISE|KNO3 (m1), (100-wt%) H2O+wt% proline|K-ISE over total ionic strengths from 0.001 to 3.000molkg−1 for different series of salt molal ratios r (r=mKCl/mKNO3=0.1,1,2.5,5.0,10.0) and pure KCl in mixed solvent system containing 5% mass fraction of proline at T=298.2 and 303.2K. The PVC based potassium and nitrate ion selective electrodes (K, NO3-ISE) and Ag–AgCl electrode used in this work were prepared in our laboratory and had a reasonably Nernst response. The activity coefficients data were interpreted based on the Harned rule and Pitzer model. The unknown Pitzer mixing interaction parameters (θClNO3,ψKClNO3) were evaluated for the studied mixed electrolyte system according to Pitzer graphical method .Then, the parameters obtained with the Pitzer model were used to calculate the values of the mean activity coefficients of KNO3, the osmotic coefficients, and the excess Gibbs free energies for the whole series of the studied mixed electrolyte system.

Determination of thermodynamic properties of the ternary electrolyte system {CoCl2 + Co(NO3)2 + H2O} by the potentiometric method at T = 298.15

In this work, the Pitzer ion interaction model and Harned rule were used to illustrate the ternary electrolyte system {CoCl2+Co(NO3)2+H2O}. The activity coefficients were determined using a potentiometric method. The galvanic cell used had no liquid junction of type: Co2+-ISE|CoCl2 (mA), Co(NO3)2 (mB), H2O|Ag.AgCl. The measurements were performed at T=298.15K and at total ionic strengths from 0.001 to 6.000mol·kg−1 for different series of salt ratios r=mCoCl2mCo(NO3)2=1.00, 2.50, 5.00, 7.50, 10.00 and 15.00. The PVC based cobalt ion-selective electrode (Co2+-ISE), the PVC based nitrate ion-selective electrode (NO3−-ISE) and the Ag/AgCl electrode used in this work were prepared in our laboratory and showed a reasonably good Nernst response. The experimental results showed that both Pitzer model and Harned rule were suitable to be used satisfactorily to describe this ternary system.

All-solid-state nitrate-selective electrode and its application in drinking water

An all-solid-state nitrate-selective electrode with the implementation of graphene as the ion-to-electron transducer was reported. The charge-transfer process was examined by electrochemical impedance spectroscope and the hydrophobic nature of the graphene film was characterized via the potentiometric water layer test. The analytical performance of the nitrate-selective electrode was investigated by the determination of nitrate in drinking water. The obtained results showed that graphene can significantly facilitate the ion-to-electron transducer and prevent the formation of water layer between the ion-selective membrane and the graphene layer. The fabricated nitrate-selective electrode displayed a Nernstian slope of 57.9mV per decade of nitrate concentration, a low detection limit of 3×10−5M and a rapid response time (within 10s) for concentration upon 10−4M. The determination of real samples indicated that the constructed nitrate-selective electrode was capable of monitoring nitrate in drinking water, providing a handy alternative for routine analysis.

Thin layer coulometric determination of nitrate in fresh waters

A nitrate ion-selective electrode (ISE) employing a permeable tubular membrane impregnated with a conventional ISE cocktail has been used successfully in the coulometric analysis of nitrate in fresh waters. The liquid ISE membrane comprising a nitrate ionophore [tridodecylmethylammonium nitrate (TDMAN)], lipophilic electrolyte [tetradodecyl-ammoniumtetrakis(4-chlorophenyl)borate (ETH 500)] and plasticizer [bis(3-ethyl-hexyl)sebacate (DOS)] was supported on a porous polypropylene tube. Coulometric analysis with the tubular membrane ISE showed that nitrate could be detected in the range 10–100μM with a precision of 2.3% relative standard deviation (RSD), limit of detection of 1.1μM and relative accuracy of 4.4% compared to a certified reference material (CRM) Lake sample.

Monitoring nytratov and measures in's noise in rastytelnoy products

Целью работы является проведения мониторинга плодоовощной продукции на содержание нитратов и разработка рекомендаций по их уменьшению. Приведены результаты определения нитратов в овощах и плодах, чаще всего используют на территории Украины в рационе питания человека. Контроль содержания нитратов проводился потенциометрическим методом с помощью нитратселективного электрода на ионометре И-160

Surfactant modified zeolite carbon paste electrode (SMZ-CPE) as a nitrate selective electrode

A nitrate-selective electrode based on surfactant-modified zeolite (SMZ) particles into carbon paste was proposed (SMZ-CPE). The electrode was fully characterized in terms of composition, response time, ionic strength, thermal stability and usable pH range. The electrode containing 10% SMZ exhibited linear response range to nitrate species in the range of 1.00 × 10 −6 to 1.00 × 10 −3 M with a detection limit of 1.00 × 10 −6 M and a Nernstian slope of 59.4 ± 0.7 mV per decade of nitrate concentration. The response of the electrode to nitrate remains constant in the pH ranges of 3.5–9.8 and 1.7–10.5 for 1.00 × 10 −4 and 1.00 × 10 −2 M nitrate, respectively, and in presence of 1 × 10 −4 to 1 × 10 −3 M NaCl. The response of the electrode reaches to its equilibrium value within several seconds (10 s) after immersing the electrode in nitrate solution. Selectivity coefficients showed multivalent anions (such as arsenate, dichromate and sulfate) have higher interferences than monovalent anions (such as iodide, fluoride, bromide, chloride and thiocyanate). The electrode was used for determination of nitrate in an ammonium nitrate fertilizer sample, using direct potentiometry, and the satisfactory results were obtained. The electrode was also used for the potentiometric titration of nitrate. The validation of the obtained results in each case was proved by statistical “ t” and “ g” tests.

Anion recognition through amide-based dendritic molecule: A poly(vinyl chloride) based sensor for nitrate ion

Poly(vinyl chloride) (PVC)-based membranes of N,N-bis-succinamide-based dendritic molecule with tetrabutyl ammonium bromide (TBAB) as a cation inhibitor and dibutylphthalate (DBP), dioctylphthalate (DOP), dibutyl (butyl) phosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and used as nitrate ion-selective electrodes. Optimum performance was observed with the membrane having I–PVC–TBAB–DBP in the ratio 1:33:1:65 (w/w). The electrode has a linear response to nitrate with a detection limit of 3.9 × 10 −5 ± 0.07 M and Nernstian compliance (57.0 ± 0.2 mV/decade) between pH 2.8 and 9.6 with a fast response time of about 20 s. The selectivity coefficient values of the order of 0.001 for mono-; bi- and trivalent anions; indicate high selectivity for nitrate ions over these anions. The preparation procedure of the electrode is very easy and inexpensive. The electrodes were used over a period of 45 days with good reproducibility. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nitrate ions in waste water samples.

Herbicide Residues and Nitrate Concentration in Tubers of Table Potatoes

This study examined Wiking-cultivar table potato tubers in a field experiment conducted between 2002 and 2004 using a rye complex soil. The experimental factors included (a) two methods of tillage, including traditional and simplified, as well as (b) seven methods of cultivation with the use of herbicides as follows: 1, control without herbicides; 2, Plateen 41.5 WG; 3, Plateen 41.5 WG + Fusilade Forte 150 EC; 4, Plateen 41.5 WG + Fusilade Forte 150 EC + adjuvant Atpolan 80 EC; 5, Barox 460 SL; 6, Barox 460 SL + Fusilade Forte 150 EC; and 7, Barox 460 SL + Fusilade Forte 150 EC + adjuvant Atpolan 80 EC. Determination of residues was performed using high-performance liquid and gas chromatography. Only trace quantities of bentazone (Barox 460 SL) were found in potato tubers, amounts that fell below the maximum residue limit (MRL). The nitrate content of potato tubers was determined using a nitrate ion-selective electrode and silver chloride reference electrode. The nitrate content in fresh matter of unpeeled and peeled tubers depended significantly only on weather conditions in the years of study. In contrast, agrotechnical procedures such as methods of tillage and cultivation did not significantly affect potato tuber nitrate content.

Microfluidic Polymer Chip with an Embedded Ion-Selective Electrode Detector for Nitrate-Ion Assay in Environmental Samples

A nitrate ion-selective electrode (NO(3)(-)-ISE) has been developed based on tetradodecylammonium bromide as an anion exchanger and 2-nitrophenyl octyl ether as a plasticizer. The NO(3)(-)-ISE shows an almost Nernstian response to nitrate ion over a concentration range between 1.0 x 10(-6) and 1.0 x 10(-1) M, with an anionic slope of -57.7 +/- 0.7 mV/decade. The selectivity coefficients of the NO(3)(-)-ISE for nitrate ion against chloride and sulfate (log k(NO(3)(-)Cl(-))(pot) = -2.42 and log k(NO(3)(-)SO(4)(2-))(pot) = -4.33) were obtained. A microfluidic polymer chip was fabricated using polystyrene plates and stainless-steel wires as a template for the channel. The microfluidic polymer chip is composed of a mixing chip and a NO(3)(-)-ISE detector chip. The microfluidic polymer chip, integrated with a NO(3)(-)-ISE detector consisting of the NO(3)(-)-ISE and a Na(+)-ISE as a reference electrode, showed an almost Nernstian response to nitrate ion over a concentration range between 1.0 x 10(-5) and 1.0 x 10(-1) M, with an anionic slope of -54.3 +/- 1.3 mV/decade. The microfluidic polymer chip was then applied to the determination of nitrate ion in environmental water samples, such as a tap water, a well-water sample and water for agricultural use.

EVALUATION OF A PORTABLE NITRATE ION-SELECTIVE ELECTRODE WITH AQUEOUS POTASSIUM NITRATE AND VEGETABLE JUICE

The nitrate ion content of vegetables has become a concern with regard to human health. A portable nitrate ion-selective electrode (ISE) developed by Horiba, Ltd. was evaluated against an aqueous solution of potassium nitrate and vegetable juice. The ISE exhibited a linear dynamic range from 20 to 6000 ppm NO 3 - in standard aqueous solutions of potassium nitrate. In vegetable juice, the measured nitrate ion concentration decreased proportionately with dilution, and was constant as a function of temperature. In nitrate-spiked samples of raw vegetable juice, the recovery percentage consistently approached 100%. Furthermore, the ISE results were essentially identical to those obtained by ion chromatography (IC), exhibiting a correlation coefficient of R=0.997 (n=7). The use of an ionic strength adjustor was deemed unnecessary in these experiments, which allows for simple implementation in practical applications. The instrument is currently commercially available as the compact nitrate ion meter B-343 (Horiba Ltd, Kyoto, Japan).

Nitrate-Selective Electrodes Based on the Trinuclear Chromium(III) Pivalates

The paper describes the analytical potentialities of the trinuclear chromium(III) complexes as potentiometric ionophores for the construction of electrodes sensitive to the presence of nitrate anion. The electroactive material containing 4,4’-bipyridil was synthesized in situ. The membrane was prepared using dioctylphthalate as a solvent mediator and poly (vinyl chloride) as a polymeric matrix. The electrodes presented a slope of 56 mV/decade, a low limit of detection (3,2.10-6 mol/l), an adequate lifetime (4 months), and suitable selectivity characteristics when compared with other nitrate electrodes. The good parameters of this electrode made possible its application to the determination of nitrate in different types of fertilizers.

Nitrate-containing ionic liquids as active membrane components of nitrate-selection electrodes

Two dialkylimidazolium nitrate ionic liquids (ILs) have been tested for use as an active component of plasticized PVC membranes in nitrate ion selective electrodes (ISEs). The potentiometric reversibility and the main electrochemical characteristics of the ISEs in KNO3 solutions have been studied. The test membranes contain 5% of the active component and demonstrate a near-Nernstian response to NO 3 − . The use of a more hydrophobic IL based on dioctadecylimidazolium increases the sensitivity and decreases the detection limit: the slope of the electrode function is 57 mV/pC, and C min = 3.7 · 10−6 mol/L. The pH range of the membrane performance has been studied, and the potentiometric selectivity to NO 3 − in the presence of several foreign anions has been determined. The new electrode exceeds the commercially available analogue (an ELIT 021 nitrate-selective electrode) in the detection limit and response time. The utility of the new electrode for the direct potentiometric determination of nitrate ILs in aqueous solutions has been demonstrated.

Sulfonated poly(ether ether ketone), an ion conducting polymer, as alternative polymeric membrane for the construction of anion-selective electrodes

A novel arrangement for polymeric membranes used in anion-selective electrodes is presented. Sulfonated poly(ether ether ketone) (SPEEK), an ion conducting polymer has been used as a polymeric matrix to build an anion-selective electrode (ISE). A NO 3 −-ISE has been chosen as a model electrode to study the efficiency of the polymeric membrane. The effect of membrane composition and polymer compatibility with the electro-active components was investigated. The polymer matrix showed good mechanical properties and can be solvent cast in complete analogy to traditional ISE membranes. SPEEK matrix was studied in order to optimize both the potentiometric response and the selectivity of the electrode. The electrode exhibited a linear response with a slope of −51 mV per decade within the concentration range from 8.0 × 10 −5 to 2.5 × 10 −2 M nitrate ion. The detection limit was found to be 5.0 × 10 −5 M, and electrodes could be used over a wide pH range of 4–8. Finally, the sensor showed improved selectivity in comparison to some of the previously reported nitrate-selective electrodes.

Nitrate-selective electrode based on a cyclic bis-thiourea ionophore

Compounds containing urea and thiourea groups can hydrogen bond oxoanions and, as such, represent a class of potential ionophores for anion-selective electrodes. We have evaluated cyclic and linear bis-thiourea compounds as ionophores in polymer membrane ion-selective electrodes. An improvement in the selectivity coefficient of nitrate against chloride of greater than one order of magnitude was observed with the cyclic ionophore in comparison to the Hofmeister lipophilicity series ( log K N O 3 − , C l − pot of −3.50 with ionophore versus −2.40 with no bis-thiourea ionophore), indicating the preference of the cyclic ionophore for nitrate. This preference for nitrate over chloride may be attributed to the spatial arrangement of the thiourea hydrogen atoms, which are capable of forming hydrogen bonds with nitrate, as well as the size of the ionophore binding cavity. In the lowest-energy conformation, all thiourea hydrogen atoms point toward a putative nitrate binding site, likely contributing to enhanced coordination.

A Sensitive Nitrate Ion-Selective Electrode from a Pencil Lead. An Analytical Laboratory Experiment

Nitrate ion is an important environmental and human health analyte and thus its detection and quantification is considered essential. This article summarizes a simple procedure for preparing and testing a nitrate ion-selective electrode based on doped polypyrrole films. Everyday pencil leads were used as a substrate for the electrochemical deposition of polypyrrole. Nitrate-doped polypyrrole electrodes, tested potentiometrically for their response to varying NO3–concentrations, exhibited Nernstian behavior (slopes of 54–55 mV per log cycle of nitrate concentration at T = 22°C), with a linear response to nitrate concentrations spanning three orders of magnitude (0.1–1× 10–4 M of NO3–) and a detection limit of 5 ± 1 × 10–5 M of nitrate. The procedure outlined here has the potential to initiate and motivate students with interests in sensor development, micro-fabrication procedures, advanced monitoring of environmental problems, and creating solutions to those problems.

The Potentiometric Studies on the Effects of Various Functional Groups in Disiloxane as an Anion-Selective Ionophore

The potentiometric responses for various anions are investigated with membrane electrode (membrane 1) based on 1,3-diethyl-1,3-dihydroxy-1,3-bis(2-dimethylaminomethyl ferrocenyl) disiloxane. The nitrate ion-selective electrode based on compound 1 gave a good Nernstian response of 58.18 mV per decade for nitrate with the detection limit of −e5.66 of log [NO3−e]. Compound 1 has all those functional groups and the other two compounds have less functional group of ferrocenyl or ferrocenyl and hydroxide, respectively. Even though, potentiometric response to anions was excellent at pH 5, the selectivity pattern for all three membrane electrode based on series of disiloxane is almost like Hofmeister sequence at pH 5. However, the membrane electrode 1-3 exhibited very different response to anions at pH 7. In this pH, NH2 is not protonated and ionophore may act as neutral carrier. Hydrogen bond may enhance the responsibility to hydrogen acceptors and intramolecular electro-active site may increase the permeability of analyte to ionophore in membrane.

New PVC Nitrate-Selective Electrode: Application to Vegetables and Mineral Waters

The paper refers the analytical potentialities of the oxa-azamacrocycles as potentiometric ionophores for the construction of electrodes selective to nitrate. Afterward, the membrane selective to nitrate is designed and optimized using a [3.3.3.3]oxazane as an ionophore. The membrane was prepared using dibutylphthalate as a solvent mediator, tetraoctylammonium as a lipophilic membrane additive, and poly(vinyl chloride (PVC) as a polymeric matrix, applied directly onto a conductive graphite/epoxy resin support. The electrodes presented a slope of 60 +/- 0.1 mV log(-1), a low limit of linear response of 4.2 x 10(-6) mol L(-1), a useful lifetime of 1 year, and improved selectivity characteristics when compared with other nitrate electrodes. The good working characteristics of this electrode, constructed without inner-reference solution, made possible its application to the determination of nitrate in different types of vegetables and bottled mineral waters without the use of a conditioning solution. The application of a significant F test proved that the results obtained were similar to those attained by application of the brucine spectrophotometric method adopted as a reference technique. Linear regression analysis also showed good agreement between the results obtained by the proposed method and the reference one.

Development and environmental application of a nitrate selective microsensor based on doped polypyrrole films

This work describes the development and testing of a sensitive and selective potentiometric nitrate microsensor based on doped polypyrrole films. Utilizing 6–7 μm carbon fibers as a substrate for pyrrole electropolymerization allowed fabrication of flexible, miniature and inexpensive sensors for in situ monitoring of nitrate. The sensors have a rapid response (several seconds) and in their characteristics are competitive with expensive commercial nitrate ion selective electrodes (ISE), exhibiting Nernstian behavior (slopes 54 ± 1 mV per log cycle of nitrate concentration ( n = 8), at T = 22 °C), a linear response to nitrate concentrations spanning three orders of magnitude (0.1–10 −4 M or 6200–6.2 ppm of NO 3 −), and a detection limit of (3 ± 1) × 10 −5 M (1.25–2.5 ppm). After a 2-month-period, the response was unchanged, and after 4.5 months, one version of the electrode continued to exhibit significant sensitivity to nitrate. Several polypyrrole nitrate microsensors were embedded sequentially downstream from a point source of nitrate solution in an intermediate scale physical groundwater model as a test of their performance under simulated environmental conditions. The microsensors responded appropriately to the approaching nitrate solution front, demonstrating dispersion and attenuation of the nitrate concentrations that increased with distance from the source.