Selective thiocyanate poly(vinyl chloride) membrane based on a 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane-Ni(II) perchlorate

A highly selective poly(vinyl chloride) (PVC) membrane electrode based on 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane-Ni(II) as a membrane carrier with unique selectivity toward thiocyanate is reported. The influence of membrane composition, pH and foreign anions were investigated. The sensor exhibits a Nernstian response for thiocyanate over a wide concentration range of 3.3×10⁻⁶ to 0.10 M, with a slope 58.4±0.3 mV per decade. The limit of detection is 3.0×10⁻⁶ M SCN⁻. The sensor has a response time of <20 s and can be used for at least 2 months without any considerable divergence in potential. The proposed electrode shows fairly a good discriminating ability towards SCN⁻ ion in comparison to other anions. It was successfully applied to direct determination of thiocyanate in urine and saliva and it was also used as an indicator electrode in titration of thiocyanate with Ag⁺ ions.     

Lanthanum-selective membrane electrode based on 2,2′-dithiodipyridine

In this study, a new poly(vinyl chloride) (PVC) membrane sensor for La³⁺ ion based on 2,2′-dithiodipyridine as an ion carrier was prepared. This electrode revealed good selectivity for La³⁺ over a wide variety of other metal ions. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of La³⁺ sensor were investigated. The electrode exhibited a Nernstian slope of 20.0 ± 1.0 mV per decade of La³⁺ over a concentration range of 7.1 × 10⁻⁶ to 2.2 × 10⁻² M of La³⁺ in the pH range 3.3-8.0. The response time was about 7 s and the detection limit was 3.1 × 10⁻⁶ M. The electrode can be used for at least 2 months without a considerable divergence in potential. The proposed electrode was used as an indicator electrode in potentiometric titration of oxalate and fluoride ions and was applied for determination of F⁻ ion in mouthwash solution.     

A chloride selective sensor based on a calix[4]arene possessing a urea moiety

New calix[4]arene derivative 1 of 1,3-alternate conformation with a ureido moiety has been synthesized in high yield and examined for its anion recognition abilities towards anions such as fluoride, chloride, bromide, iodide, nitrate and acetate by ¹H NMR and UV-vis spectroscopy. The results show that receptor has strong binding affinity for chloride ions. A chloride ion selective electrode (ISE) was also formed which showed excellent selectivity over all the other anions tested. The limit of detection is 2.51 × 10⁻⁵ mol dm⁻³.     

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 × 10⁻² to 1 × 10⁻⁶ M CPC at 25 °C over the pH range 2-8 with cationic slope 60.66 ± 1.10. The lower detection limit is found to be 8 × 10⁻⁷ M and response time of about 3 s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D. = 0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.     

Nickel(II)-selective sensor based on dibenzo-18-crown-6 in PVC matrix

Nickel(II)-selective sensors have been fabricated from poly(vinyl chloride) (PVC) matrix membranes containing neutral carrier dibenzo-18-crown-6 as electroactive material, sodium tetraphenylborate (NaTPB) as an anion excluder and tris-(2-ethylhexyl) phosphate (TEHP) as plasticizing solvent mediator. The membrane having the composition of crown ether:NaTPB:TEHP:PVC in the ratio 10:1:200:200 (w/w) exhibits best results with linear potential response in the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M and a Nernstian slope of 29.5 mV/decade of activity between 2.6 and 6.8. The sensor exhibits a fast response time of <25 s, is inert towards non-aqueous medium up to 15% (v/v) and was used over a period of 4 months with good reproducibility. It is selective over a number of mono-, bi- and trivalent cations. The practical utility of the sensor has been demonstrated by using it as an indicator electrode in the potentiometric titration of Ni²⁺ against EDTA and also for the estimation of Ni²⁺ in some Indian brand chocolates.     

Determination of trace iodide in iodised table salt on silver sulfate-modified carbon paste electrode by differential pulse voltammetry with electrochemical solid phase nano-extraction

Electrochemical solid phase nano-extraction, a novel sample preparation technique, was used for the determination of trace iodide in iodised table salt based on the silver sulfate nanoparticle-modified carbon paste electrode. Electrochemical solid phase nano-extraction was realized in the exchange between the sulfate anion in nanoparticles and an iodide anion from aqueous solution. The released silver cation serves as the electrochemical probe for the determination of iodide. The extraction follows a Freundlich adsorption isotherm, and can be used in the detection of iodide in the concentration range 5.0 × 10⁻¹²-4.0 × 10⁻⁹ M. The amount of iodide in iodised table salt was determined as 0.875 ± 0.002 μg/g, which is about 2.5% of the addition amount of iodate with a relative deviation of 5.92% and a standard addition recovery of 90-110%. The large amounts of chloride and iodate did not interfere with the detection.     

Novel platinum(II) selective membrane electrode based on 1,3-bis(2-cyanobenzene)triazene

A plasticized poly (vinyl chloride) membrane electrode based on 1,3-bis(2-cyanobenzene)triazene (CBT) for highly selective determination of platinum(II) (in PtCl₄²⁻ form) is developed. The electrode showed a good Nernstian response (29.8 ± 0.3 mV decade⁻¹) over a wide concentration range (1.0 × 10⁻⁶ to 1.0 × 10⁻² mol L⁻¹). The limit of detection was 5.0 × 10⁻⁷ mol L⁻¹. The electrode has a response time of about 40 s, and it can be used for at least 1 month without observing any considerable deviation from Nernstian response. The proposed electrode revealed an excellent selectivity toward platinum(II) ion over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, and it could be used in the pH range of 3.2-5.1. The practical utility of the electrode has been demonstrated by its use in determination of platinum ion in, alloy, tap, mineral and river water samples.     

An optical redox chemical sensor for determination of iodide

A novel optical sensor based on a redox reaction for the determination of iodide has been developed. The optode membrane is constructed by immobilization of methyltrioctylammonium chloride on triacetylcellulose polymer. The exchange of chloride as counter ion with iodate in the membrane changes the color to yellow, when it is placed in acidic solution of iodide. The sensor can readily be regenerated by 0.1 mol L⁻¹ NaOH in less than 15 s. The optode has a linear range of 3.94 × 10⁻⁶ to 5.51 × 10⁻⁵ mol L⁻¹ of iodide ions with a limit of detection 7.44 × 10⁻⁷ mol L⁻¹. The relative standard deviation for eight replicate measurements of 3.94 × 10⁻⁶ and 1.57 × 10⁻⁵ mol L⁻¹ of iodide was 2.83 and 1.38%, respectively. The sensor was successfully applied to the determination of iodide in tablet, powdered milk and urine samples.     

A cobalt(II)-selective PVC membrane based on a Schiff base complex of N,N′-bis(salicylidene)-3,4-diaminotoluene

A new PVC membrane electrode for Co²⁺ based on N,N′-bis(salicylidene)-3,4-diaminotoluene, an excellent neutral carrier, has been fabricated using sodium tetraphenylborate (NaTPB) as an anionic excluder and dioctylphthalte (DOP) as a solvent mediator. The electrode exhibits a linear potential response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M with a slope of 30 ± 0.2 mV per decade. The detection limit of the proposed sensor is 5.0 × 10⁻⁸ M and it can be used over a period of 5 months. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals and could be used in the pH range of 2.0-9.0. This electrode was successfully applied for the determination of Co²⁺in real samples and as an indicator electrode in potentiometric titration of cobalt ions.     

Sequential injection system for simultaneous determination of chloride and iodide by a Gran’s plot method

This paper describes an automated set-up based on the sequential injection analysis (SIA) concept with potentiometric detection for the determination of chloride and iodide at low concentrations. The assessment of both ion concentrations is accomplished by titration with silver ions using the Gran’s plot approach. The proposed procedure enables chloride and iodide to be determined simultaneously in the range 6.0×10⁻⁶ to 1.0×10⁻⁴ mol l⁻¹ if a minimum silver concentration in the volumetric solution is chosen (5×10⁻⁵ mol l⁻¹). Conventional titrations based on the first derivative evaluation of the equivalence points applied to the same solutions fail, especially for chloride determinations. Although, a comparison of results obtained for higher analyte concentrations shows that they have similar accuracy and precision.     

A highly selective fluorescent sensor for Cu based on 2-(2′-hydroxyphenyl)benzoxazole in a poly(vinyl chloride) matrix

This paper describes a copper selective optical chemical sensor based on static quenching of the fluorescence of 2-(2′-hydroxyphenyl)benzoxazole entrapped in a poly(vinyl chloride) (PVC) membrane. The effect of the composition of the sensing membrane was studied, and experimental conditions were optimized. The sensors exhibit stable response over the concentration range from 4.0 × 10⁻⁸ M to 5.0 × 10⁻⁵ M Cu²⁺ at pH 4.0-6.5, and a high selectivity. The response time for Cu²⁺ with concentration ≤5 × 10⁻⁶ M is less than 7 min. The optode can be regenerated using 0.1 M HCl and acetate buffer solution. The sensor has been used for direct measurement of copper content in river water samples with a relative error less than 4% with reference to that obtained by atomic absorption spectrometry.     

Sub-micro level monitoring of beryllium ions with a novel beryllium sensor based on 2,6-diphenyl-4-benzo-9-crown-3-pyridine

The 2,6-diphenyl-4-benzo-9-crown-3-pyridine (DPCP) was used as an excellent ionophore in construction of a coated graphite poly(vinyl chloride) (PVC)-based membrane sensor. The best performance was obtained with a membrane composition of 30% poly(vinyl chloride), 60% o-nitrophenyloctyl ether (NPOE), 5% 2,6-diphenyl-4-benzo-9-crown-3-pyridine and 5% sodium tetraphenyl borate (TBP). This sensor shows very good selectivity and sensitivity towards beryllium ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The sensor revealed a great enhancement in selectivity coefficients and sensitivity for beryllium, in comparison with the previously reported beryllium electrodes. The electrode exhibits a Nernstian behavior (with slope of 29.6 mV per decade) over a very wide concentration range (1.0×10⁻⁷ to 1.0×10⁻¹) with a detection limit of 4.0×10⁻⁸ M (360 pg ml⁻¹). It shows relatively fast response time, in whole concentration range (<10 s), and can be used for at least 12 weeks in the pH range of 4.5-8.0. The proposed sensor was successfully used to determination of beryllium in mineral ore.     

No more conventional reference electrode: Transition time for determining chloride ion concentration

Ion selective electrodes (ISE) are used extensively for the potentiometric determination of ion concentrations in electrolytes. However, the inherent drift in these measurements and the requirement of a stable reference electrode restrict the feasibility of this method for long-term in-situ applications. This work presents a chronopotentiometric approach to minimize drift and avoid the use of a conventional reference electrode for measuring chloride ion concentration. An anodic current pulse is applied to a Ag/AgCl working electrode which initiates a faradaic reaction that depletes the chloride ions near the electrode surface. The rate of change in potential at the Ag/AgCl electrode, due to chloride ion depletion, reaches an inflection point once the chloride ions deplete completely near the electrode surface. The moment of the inflection point, also known as the transition time, is a function of the chloride ion concentration and is described by the Sand equation. It is shown that the square root of the transition time is linearly proportional to the chloride ion concentration. Drift in the response over two weeks is negligible: 59 μM/day when measuring 1 mM of Cl⁻ ions using a 10 A m⁻² current pulse. The transition time at a specific ion concentration can be tuned by the applied current pulse, e.g., in a solution containing 5 mM chloride ions, the transition times with current pulses of 10 and 20 A m⁻² are 1.56 and 0.25 s, respectively. The moment of inflection determines the response, and thus is independent of the absolute potential of reference electrode. Therefore, any metal wire can act as a pseudo-reference electrode, enabling this approach for long-term and integrated-sensor applications such as measurement inside concrete structures.     

Efficient condensation of carboxylic acids with alcohols catalyzed by fluorous ammonium triflates

The use of fluorous ammonium salts as metal-free catalysts for the direct condensation of equimolar amounts of carboxylic acids and aliphatic alcohols has been investigated. Esterification reactions were thus conveniently carried out under mild fluorous biphasic conditions, in the presence of 1 mol % of fluorous ammonium triflate and without recourse to any additional water removal technique. Good to excellent ester yields were obtained in the case of primary and secondary aliphatic alcohols. The fluorous salt was easily recovered by simple phase separation and reused at least three times without considerable loss of activity.     

Highly selective and sensitive copper membrane electrode based on a new synthesized Schiff base

Bis(2-hydroxyacetophenone)butane-2,3-dihydrazone (BHAB) was used as new N-N Schiffs base which plays the role of an excellent ion carrier in the construction of a Cu(II) membrane sensor. The best performance was obtained with a membrane composition of 30% poly(vinyl chloride), 55% o-nitrophenyloctyl ether (NPOE), 7% BHAB and 8% oleic acid (OA). This sensor shows very good selectivity and sensitivity towards copper ion over a wide variety of cations, including alkali, alkaline earth, transition and heavy metal ions. The effect of membrane composition and pH and influence of additive anionic on the response properties of electrode were investigated. The electrode exhibits a Nernstian behavior (with slope of 29.6 mV per decade) over a very wide concentration range (5.0 × 10⁻⁸ to 1.0 × 10⁻² mol L⁻¹) with a detection limit of 3.0 × 10⁻⁸ mol L⁻¹ (2.56 ng mL⁻¹). It shows relatively fast response time, in whole concentration range (<15 s), and can be used for at least 12 weeks in the pH range of 2.8-5.8. The proposed sensor was successfully used to determination of copper in different water samples and as indicator electrode in potentiometric titration of copper ion with EDTA.     

Highly selective thiocyanate membrane electrode based on butane-2,3-dione bis(salicylhydrazonato)zinc(II) complex

A highly selective poly(vinyl chloride) (PVC) membrane electrode based on butane -2,3-dione bis(salicylhydrazonato) zinc(II) [Zn (BDSH)] complex as carrier for thiocyanate-selective electrode is reported. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. The sensor responds to thiocyanate in linear range from 1.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a slope −56.5 ± 1.1 mV decade⁻¹, over a wide pH range of 3.5-8.5. The limit of detection of the electrode was 7.0 × 10⁻⁷ M SCN⁻. Selectivity coefficients determined with fixed interference method (FIM) indicate a good discriminating ability towards SCN⁻ ion in comparison to other anions. The proposed sensor has a fast response time of about 5-15 s and can be used for at least 3 months without any considerable divergence in potential. It was applied as indicator electrode in titration of thiocyanate with Ag⁺ and in potentiometric determination of thiocyanate in saliva and urine samples.     

A cerium(III) selective polyvinyl chloride membrane sensor based on a Schiff base complex of N,N'-bis[2-(salicylideneamino)ethyl]ethane-1,2-diamine

A polyvinyl chloride (PVC) based membrane sensor for cerium ions was prepared by employing N,N′-bis[2-(salicylideneamino)ethyl]ethane-1,2-diamine as an ionophore, oleic acid (OA) as anion excluder and o-nitrophenyloctyl ether (o-NPOE) as plasticizer. The plasticized membrane sensor exhibits a Nernstian response for Ce(III) ions over a wide concentration range (1.41 × 10⁻⁷ to 1.0 × 10⁻² M) with a limit of detection as low as 8.91 × 10⁻⁸ M. It has a fast response time (<10 s) and can be used for 4 months. The sensor revealed a very good selectivity with respect to common alkali, alkaline earth and heavy metal ions. The response of the proposed sensor is independent of pH between 3.0 and 8.0. It was used as an indicator electrode in potentiometric titration of fluoride, carbonate and oxalate anions and determination of cerium in simulated mixtures.     

Flow injection potentiometric determination of clobutinol hydrochloride

New clobutinol (Clob) ion-selective polyvinyl chloride (PVC) membrane electrodes, based on the ion-associates of Clob with phosphotungstic acid or phosphomolybdic acid were prepared using dibutyl phthalate as plasticizing solvent. The electrodes were characterized in terms of membrane composition, temperature and pH. The sensors showed a near-Nernstian response over the concentration ranges (6.31 × 10⁻⁶)-(1.00 × 10⁻²) and (5.01 × 10⁻⁵)-(1.00 × 10⁻²) M in the case of clobutinol-phosphotungstate ((Clob)₃-PT) applying batch and flow injection (FI) analysis, respectively, and (1.58 × 10⁻⁵)-(1.00 × 10⁻²) and (5.01 × 10⁻⁵)-(1.00 × 10⁻²) M in case of clobutinol-phosphomolybdate ((Clob)₃-PM) for batch and FI analysis systems, respectively. The electrodes were successfully applied for the potentiometric determination of ClobCl in pharmaceutical preparation and urine in steady state and flow injection conditions. The electrodes exhibit good selectivity for Clob with respect to a large number of inorganic cations, sugars and amino acids.     

Ion imprinted polymer based ion-selective electrode for the trace determination of dysprosium(III) ions

Ion-selective electrode (ISE) was designed by dispersing the dysprosium(III) IIP particles in 2-nitrophenyloctyl ether plasticizer and then embedded in polyvinyl chloride matrix. The ISE shows a Nernstian response for dysprosium(III) over a wide concentration range (8.0 × 10⁻⁶ to 1.0 × 10⁻¹ M) with a slope of 21.7 mV per decade. The limit of detection was 2 × 10⁻⁶ M. This sensor has a very fast response time (∼10 s) and offers high selectivity compared to conventional chemical sensors towards dysprosium(III) with respect to several alkali, alkaline earth and transition metal ions as the selectivity is 10-100-fold better. The sensor was used for determination of dysprosium(III) ions by potentiometric (EDTA) titration and has been successfully demonstrated for the determination of fluoride in mouth wash solution.     

Amperometric biosensor based on a nanoporous ZrO2 matrix

A biosensor was investigated based on the use of ZrO₂ sol-gel matrix for enzyme immobilization in the mild condition. This bioceramic zirconia alcogel has been prepared by the novel alcohothermal route with a cheap inorganic salt Zr(NO₃)₄·5H₂O with several desirable features including a large surface area (about 460 m² g⁻¹) as well as pore volume and a well-developed textural mesoporosity, and horseradish peroxidase was selected as a model enzyme. The results of transmission electron microscopy (TEM) and BET measurement of the substrate showed that the as-prepared zirconia matrix has an advantageous microenvironment and large surface area available for high enzyme loading. The parameters affecting both the entrapment of enzyme and the biosensor response were optimized. The resulting biosensor exhibited high sensitivity of 111 μA mM⁻¹ for hydrogen peroxide over a wide range of concentrations from 2.5×10⁻⁷ to 1.5×10⁻⁴ mol l⁻¹, quick response of less than 10 s and good stability over 3 months.