A new ion-selective electrode for nitrate determination

Summary A new ion-selective electrode which can be used for the nitrate determination in a concentration range of 10^–1 to 10^–4 mol/l is described. The polymer ion-exchanger membrane is formed by an epoxy resin, after Nitron nitrate having been introduced serving as an anchor group. The selectivity constants k _t-i have been determined for Cl^–, ClO ₄ ^– , HCO ₃ ^– , SO ₄ ^2– , HPO ₄ ^2– , MoO ₄ ^2– and WO ₄ ^2– .

---

Neue ionenselektive Elektrode für die Nitratbestimmung

Zusammenfassung Es wird eine neue ionenselektive Elektrode beschrieben, die für Nitratbestimmungen im Konzentrationsbereich von 10^–1 bis 10^–4 mol/l verwendet werden kann. Die Ionenaustauschermembran besteht aus Epoxidharz, in das Nitronnitrat als Ankergruppe eingeführt wurde. Die Selektivitätskonstanten K _T-I für Cl^–, ClO ₄ ^– , HCO ₃ ^– , SO ₄ ^2– , HPO ₄ ^2– , MoO ₄ ^2– und WO ₄ ^2– wurden bestimmt.

---

---

Dedicated to Prof. Dr. H. Monien on the occasion of his 60th birthday     

Hydrogen ion-selective electrode based on an iron-hydroxo-complex

Summary A new hydrogen ion-selective based on an iron hydroxo complex was proposed. The ion sensing membrane was composed of the iron(III) hydroxo complex, membrane solvent and polyvinyl chloride. The proposed electrode using 1-decanol as the most favourable solvent showed a linear pH-response from 0 to 5 with a potential change of 56 mV per pH-unit. The characteristics of the proposed electrode and a discussion on the response mechanism are reported.

---

Wasserstoffionen-selektive Elektrode auf Basis eines Eisen-Hydroxo-Komplexes

Zusammenfassung Die Membran der vorgeschlagenen ionen-selektiven Elektrode besteht aus einem Eisen(III)-hydroxokomplex, dem Membran-Lösungsmittel und Polyvinylchlorid. Mit 1-Decanol als günstigstem Lösungsmittel ergab sich eine lineare Anzeige von pH 0 bis 5 mit einer Potentialänderung von 56 mV/pH. Die Charakteristik der vorgeschlagenen Elektrode wird beschrieben und der Ansprechmechanismus diskutiert.

     

A double-membrane ephedrine selective electrode based on ephedrine-tetraphenylborate in poly (vinyl chloride) resin

The construction and performance characteristics of a double-membrane ephedrine selective electrode are described. The electrode is based on the use of an internal conducting membrane made of tetrabutylammonium bromide and another external electroactive membrane containing the ionic pair ephedrine-tetraphenylborate in a poly (vinyl chloride) resin (with some plasticizers incorporated) as an inert matrix. The ephedrine electrode exhibits linear Nernstian response within the range 10(-2)-5 x 10(-5)M of ephedrine, with a slope of 58.2 +/- 0.5 mV decade(-1) at 25 +/- 0.2 degrees . The detection limit is 10(-4.5)M. The reproducibility (coefficient of variation) was 0.54% (n = 10 determinations) and the stability of its potential is 2.3 mV/24 h. The selectivity coefficients for 15 ions were calculated. The electrode was applied to the determination of ephedrine in some pharmaceutical preparations with satisfactory results.     

Determination of nitrate in water with a new construction of ion-selective electrode

A new design of the liquid-state electrode for nitrate ions is proposed. It contains a porous wick soaked with the liquid ion-exchanger, and has no internal reference solution. This electrode was used for nitrate determination of tap water at the level 8–10 p.p.m. The effects of chloride and hydrogencarbonate are eliminated by the addition of silver sulphate and a phosphate buffer, which also maintains constant ionic strength. Precision of a series of measurements is better than 2%, but the results show differences up to 10% compared to the colorimetric brucine procedure.     

离子选择电极阵列土壤中硝态氮测定

土壤硝态氮反映土壤短期氮素供应水平,实时了解土壤硝态氮的含量为精准农业和农业面源污染防控提供支撑,因此,在线实时检测土壤硝态氮方法突破就显得十分迫切。土壤硝态氮中的硝酸根离子在土壤中的高水溶性和流动性为全固态硝酸根离子选择电极高敏感检测土壤中硝态氮提供了条件,固态硝态氮离子选择电极的离子选择膜反应硝酸根离子在被测溶液中的浓度。采用全固态硝酸根离子选择电极,且与温度电极和pH电极融合组成电极阵列对土壤饱和溶液中的硝态根离子进行检测。设计了高输入阻抗运算放大电路对电极信号进行采集,并通过微处理控制蠕动泵完成土壤硝态氮待测溶液连续流动测量及实时传输结果。实验结果表明,电极响应时间≤15 s,斜率-51.63 mV/decade,线性范围10-5-10-2.2 mol/L,最低检测限10-5.23 mol/L。相对标准差在0.78%-4.47%范围内,加标回收率均在90%-110%以内。与国家标准紫外可见分光光度法测试结果相比,相关系数（R2）为0.9952,为土壤硝态氮在现场检测奠定技术基础。     

A solid state Cr(VI) ion-selective electrode based on polypyrrole

We report on a graphite electrode onto which polypyrrole was electrodeposited and then doped with chromate ion. This electrode can serve as a Cr(VI)-selective solid-state electrode. Electropolymerization of pyrrole was performed potentiostatically at 0.80?V (vs. SCE) using battery graphite as the working electrode in a solution containing 0.10?M of pyrrole and 20?mM of chromate. A platinum wire was used as an auxiliary electrode. The new electrode displays high selectivity, a very wide dynamic range, a sufficiently fast response time and a good shelf lifetime. It shows a linear Nernstian response over 1.0?×?10^?6 to 1.0?×?10^?1?M concentration range (with a slope of 26.55?±?0.20?mV per log of concentration). The detection limit is 0.5?μM, and the pH optimum is 7.0.

Cadmium ion-selective electrode based on tetrathia-12-crown-4

A new polyvinylchloride membrane sensor for Cd(2+) ions based on tetrathia-12-crown-4 as an ionophore was prepared. The sensor exhibits a Nernstian response for cadmium ions over a wide concentration range (4.0 x 10(-7) to 1.0 x 10(-1) M) with a slope of 29+/-1 mV decade(-1). The limit of detection is 1.0 x 10(-7) M (0.01 ppm). It has a fast response time of <10 s and can be used for at least 6 weeks without any divergence in potential. The electrode can be used in the pH range from 2.5 to 8.5. The proposed sensor shows fairly good discriminating ability towards Cd(2+) ion in comparison with some alkali, alkaline earth, transition and heavy metal ions. It was successfully applied for the direct determination of Cd(2+) in solution and, as an indicator electrode, in potentiometric titration of cadmium ions.     

A novel nitrate-selective electrode based on precipitated nitron nitrate

Summary A nitrate-selective electrode based on precipitated nitron nitrate in an epoxy resin matrix has been prepared. The lower detection limit is 10^–5 M, the optimum pH range is 2.0–8.5, and the response time is 1 min. The electrode is selective in presence of CH₃COO^–, SO₄ ^2–, C₂O₄ ^2–, PO₄ ^3–, NO₂ ^–, Cl^– and Br^–, but I^– interferes. Results for nitrate in soil samples were in agreement with values obtained spectrophotometrically.

---

Eine neue nitrat-spezifische Elektrode auf der Basis gefällten Nitronnitrats

Zusammenfassung Eine nitrat-spezifische Elektrode auf der Basis gefällten Nitronnitrats in einer Epoxyharz-Matrix wurde hergestellt. Die untere Nachweisgrenze ist 10^–5 M, das pH-Optimum liegt zwischen 2,0 und 8,5, die Reaktionszeit beträgt 1 Minute. Die Elektrode ist selektiv in Gegenwart von Acetat, Sulfat, Oxalat, Phosphat, Nitrit, Chlorid und Bromid; aber Jodid stört. Ergebnisse der Nitratbestimmung in Bodenproben stimmen mit spektrophotometrischen Resultaten überein.

---

---

Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone

A new ion-selective PVC membrane electrode based on salicylaldehyde thiosemicarbazone as an ionophore is developed successfully as sensor for mercury(II) ions. The electrode shows excellent potentiometric response characteristics and displays a linear log[Hg²⁺] versus EMF response over a wide concentration range of 1.778×10⁻⁶-1.0×10⁻¹ M with Nernstian slope of 29 mV per decade with the detection limit of 1.0×10⁻⁶ M. The response time of the electrode is less than 30 s and the membrane electrode operates well in the pH range of 1.0-3.0. The lifetime of the sensor is about 2 months. The electrode shows better selectivity towards Hg²⁺ ions in comparison with the alkali, alkaline and some heavy metal ions; most of these metal ions do not show significant interference (K^Pot_Hg,M values of the order of 10⁻³-10⁻⁴). The present sensor showed comparable or even better performance vis-à-vis similar PVC based ion-selective electrodes reported in literature. The sensor was also applied as an indicator electrode for potentiometric titration of Hg²⁺ions with I⁻ and Cr₂O₇²⁻.     

Ion chromatography detector based on solid-state ion-selective electrode array

A variety of neutral carrier type ionophores for monovalent cations were employed to prepare solid-state cation-selective electrodes (SSEs) for use as a detector in single-column ion chromatography (IC). The polyurethane-based pseudoreference electrode made it possible to assemble an array type SSE detector for IC. An SSE-based detector provides not only the overall chromatogram for the separated ion species (monensin methyl ester-nonactin-based membrane), but also the enhanced chromatogram for specified ions of interest (valinomycin as K+ and nonactin for NH4+). This feature makes it possible to perform highly quantitative analysis with low detection limits even if the separation efficiency of the ion-exchange is not sufficient. Since SSE-based IC detectors are easily miniaturized and replaceable at low cost, they are an ideal component of a portable IC system.     

Trifluoroacetate ion-selective electrode

The trifluoroacetate ion-selective electrode was prepared by using the organic solvent solution of trifluoroacetate salt of crystal violet or tris(bathophenanthroline) iron(II) chelate.The response is linear over the activity range 10^?1 to 3 × 10^?5M, with a Nernstian slope 60 mV/activity decade at 29 °C. The interferences of divalent ions, chloride, fluoride and acetate ions are extremely low. Iodide interferes greatly.     

Potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate film-modified electrode

A potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate(III) (CHCF) film-modified glassy carbon electrode is proposed. The electroactive film is introduced onto the glassy carbon electrode surface by electrodeposition of cobalt, which forms a thin CHCF film on subsequent anodic scanning in KClHCl solution (pH 5.0–5.5) containing K₃Fe(CN)₆. The thickness of the film on the electrode surface can be controlled by changing the electrodeposition time and the concentrations of cobalt(II) and Fe(CN)^3?₆ ions. The modified electrode exhibits a linear response in the concentration range 1 × 10^?1 ?3 × 10^?5 M potassium ion activity, with a near-Nernstian slope (48–54 mV per decade) at 25 ± 1°C. The detection limit is 1 × 10^?5 M. The stability, response time and selectivity were investigated. The electrode exhibits good selectivity for potassium ion with the twelve cations investigated. The relative standard deviation is 1.5% (n=10). The effects of the thickness of the electroactive film and the pH of the solution on the electrode response were also investigated.     

Sodium ion-selective membrane electrode based on a new crown ether

A sodium ion-selective PVC membrane electrode based on di(o-methoxy)stilbenzo-24-crown-8 is reported. The electrode gives a near-Nernstian response in the range 9×10^?6–1×10^?2 M sodium ion and can be used in the pH range 5–8.5. Selectivity coefficients are 1.8×10^?1 (K⁺), 2.0×10^?4 (Li⁺) 2.5×10^?2 (NH⁺₄) and about 10^?4 for Mg²⁺, Ca²⁺ and Ba²⁺.     

Chromium(III) ion-selective electrode based on 4-dimethylaminoazobenzene

A PVC-based membrane of 4-dimethylaminoazobenzene reveals a Nernstian potentiometric response (with slope of 19.5+/-0.6 mV/decade and a correlation coefficient of 0.999) for Cr(III) over a wide concentration range (1.66 x 10(-6)-1.0 x10(-2) mol dm(-3)). The potential of this electrode is independent of pH in the range of 3.0-5.5. It has a fast response time of about 10 s and was used for a period of 3 months with good reproducibility. The detection limits of this membrane electrode was 8 x 10(-7) M. the proposed electrode has been used as an indicator electrode in the potentiometric titration of Cr(III) with EDTA. This sensor exhibits a very good selectivities for Cr(III) over a wide variety of metal ions.     

A hydrogen ion-selective liquid-membrane electrode based on tri-n-dodecylamine as neutral carrier

An electrically neutral hydrogen ion-selective carrier, tri-n-dodecylamine, is used as the active component for liquid-membrane electrodes. The observed ion selectivities are superior to those of previously described pH-sensitive liquid-membrane electrodes. The electrode characteristics permit the study of intracellular as well as extracellular hydrogen ion activities.     

A new ionic strength adjustor for nitrate analysis in waters,soils and plants using ion-selective electrode

A new ionic strength adjustor, ISA (ISA-Pb) composed of 0.02M Pb(CH₃COO)₂–0.01M PbO–0.02M CH₃COOK–0.01M NH₂SO₃H, was tested for the rapid nitrate analysis of waters, soil and plant extracts by means of ion-selective electrode (ISE). It was found that nitrate can be determined accurately and precisely within the concentration range of 5 × 10^–2 M to 2 × 10^–6 M. The proposed ISA-Pb, with a pH of 6.8, controlled the interferences of Cl^–, HCO ₃ ^– , NO ₂ ^– , and organic anions effectively, and gave results comparable to those obtained by the commonly used ISA with Ag₂SO₄ (ISA-Ag) and to well established chemical methods as well. ISA-Pb is much cheaper than ISA-Ag, and can therefore economically replace the latter when ISE is used for nitrate determination.Part of the senior author's doctorate thesis     

A new ion-selective electrode for anionic surfactants

The new ligand 7-methyl-7,13-di-octyl-1,4,10-trioxa-13-aza-7-azonia-cyclopentadecane (L¹) has been designed, synthesised and used as ionophore in the development ion-selective electrodes for anionic surfactants. Different PVC-membrane anionic-surfactants-selective electrodes were prepared by using L¹ as ionophore and bis(2-ethylhexyl)sebacate (BEHS), dibutyl phthalate (DBP) and nitrophenyl octyl ether (NPOE) as plasticizers. The PVC-membrane electrode containing L¹ and NPOE (electrode E1) showed a Nernstian response to lauryl sulfate with a slope of −59.5 mV per decade in a range of concentrations from 1.3 × 10⁻⁶ to 6.8 × 10⁻³ M and a detection limit of 6.0 × 10⁻⁷ M. The electrode E1 also showed a reasonable response to other alkyl sulfates and alkylbenzene sulfonates, whereas it does not respond to carboxylates and to cationic and non-ionic surfactants. A similar electrode to E1 but additionally containing the cationic additive n-octylammonium bromide was also prepared (electrode E2) and compared with the response of E1. Selectivity coefficients for different anions with respect to lauryl sulfate were determined by means of the fixed interference method considering lauryl sulfate as the principal anion and using a concentration of 1.0 × 10⁻² mol dm⁻³ for the corresponding interfering anion. The selectivity sequence found for the electrode E1 was: LS⁻ > SCN⁻ > ClO₄⁻ > CH₃COO⁻ > I⁻ > HCO₃⁻ > Br⁻ > NO₃⁻ > NO₂⁻ > Cl⁻ > IO₃⁻ > phosphate > SO₃²⁻ > C₂O₄²⁻ > SO₄²⁻. Electrode E1 showed remarkably better selectivity coefficients than electrode E2.