Nitron tetrachloroaurate(III) electrodes with poly(vinyl chloride) and liquid membranes for the selective determination of gold

PVC matrix and liquid membrane electrodes have been developed for direct potentiometric determination of gold(III). The membranes incorporate nitron tetrachloroaurate(III) as electroactive material. Fast response for gold(III) over the concentration range 10(-5)-0.1M, with response slopes of 52.8-55.2 mV/decade is obtained. The electrodes show good selectivity for gold(III) at pH 2-5 in the presence of many anions and cations. The PVC membrane electrode offers the advantages of greater selectivity (except for Cr(3+), Mn(2+) and ClO(-)(4)) and higher thermal stability. The liquid membrane electrode gives a higher response slope and faster time of response than the PVC membrane electrode. Determination of AuCl(-)(4) over the range 2 mug/ml-2 mg/ml shows an average recovery of 98.5% and a mean standard deviation of 1.0%. Determination of gold in some gold alloys (58.3-99.9% Au) and pharmaceutical preparations gave an average recovery of 99.4% and a mean standard deviation of 0.7%, which are comparable with the performance obtained with the spectrophotometric Malachite Green and gravimetric U.S. Pharmacopeia methods.     

New liquid-membrane electrodes for direct determination of atropine in pharmaceutical preparations

Solutions of atropinium 5-nitrobarbiturate in n-octanol and atropinium picrolonate in p-nitrotoluene are used as novel liquid ion-exchangers in electrodes that respond to the atropine cation. The performance characteristics of the two electrodes are almost identical: the response is linear for 10(-5)-10(-2)M atropine with a slope of 56.5 +/- 1 mV/concentration decade. The static response times are 30-90 sec and the potential readings are stable over the pH range 3-8. There is negligible interference from a number of inorganic and organic cations, and some common excipients. In the direct determination of 1-200 mug/ml of atropine, the average recovery with both electrodes is 98% (mean standard deviation 1.7%). Atropine has been determined in some pharmaceutical preparations with an average recovery of 98% (standard deviation 1.9%), the results being in agreement with those obtained by standard methods.     

Potentiometric membrane sensors for the selective determination of pyridoxine hydrochloride (vitamin B6) in some pharmaceutical formulations

The construction and general performance characteristics of two novel potentiometric PVC membrane sensors responsive to the pyridoxine hydrochloride known as vitamin B6 (VB6) are described. These sensors are based on the use of the ion-association complexes of the pyridoxine cation with phosphomolybdate, and phosphotungstate counter anions as ion pair in a plasticized PVC matrix. The electrodes show a stable, near-Nernstian response for 6x10(-5)-1x10(-2) M VB6 at 25 degrees C over the pH range 2-4 with a cationic slope of 54.0+/-0.5 and 54.5+/-0.4 per concentration decade for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate respectively. The two electrodes have the same lower detection limit (4x10(-5) M) and the response times are 45-60 and 30-45 s in the same order for both. Selectivity coefficients for VB6 relative to a number of interfering substances were investigated. There is negligible interference from many cations, some vitamins and pharmaceutical excipients. Direct potentiometric determination of 15-2000 microg/ml pyridoxine shows an average recovery of 98.0% and 99.0% with relative standard deviation 1.5% and 1.2% at 100.0 microg/ml for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate electrodes, respectively. The determination of VB6 in some pharmaceutical preparations using the proposed electrodes gave an average recovery of 98.0 and 99.0% of the nominal value and a mean standard deviation of 1.1% and 0.9% (n=10) for pyridoxine-phosphomolybdate and pyridoxine-phosphotungstate electrodes, respectively. The results compare favorably with data obtained by the British Pharmacopoeia method.     

PVC Membrane electrodes for manual and flow-injection determination of tetraphenylborate: Applications to separate and sequential titrations of some metal ions

Three novel poly (vinyl chloride) matrix membrane electrodes, highly sensitive and selective for tetraphenylborate anion (TPB), are developed and electrochemically evaluated. They are based on the use of iron(II) bathophenanthroline, nickel(II) bathophenanthroline-and nitron-TPB ion-pair complexes as electroactive materials with dioctylphthalate (DOP) and 2-nitrophenyl phenyl ether (NPPE) as plasticizing solvent mediators. The electrodes exhibit stable and rapid near-Nernstian response for 10(-2)-10(-6)M TPB over the pH range 4-10. Use of these electrodes for direct potentiometric determination and potentiometric titration of as low as 1 mug of TPB/ml and 0.6 mg of TPB/ml give results with average recoveries of 99.3% (mean standard deviation 0.5%) and 99.4% (mean standard deviation 0.2%), respectively. Incorporation of nitron-TPB PVC sensor in a flow-through sandwich cell provides an efficient flow-injection detector for determining TPB with an input rate of at least 60 samples/hr. The limit of detection is 1.6 mug TPB/ml in a 20-mul sample. The electrodes are also used to monitor separate and sequential titrations of some metal ions with TPB. Alkaline earth and transition-metal ions upon reaction with polyethylene glycol and ethylenediamine, respectively, form cationic complexes readily titrated with TPB. Optimum conditions are outlined for sequential titrations of various combinations of metallic species.     

PVC membrane electrodes for potentiometric determination of tripelennamine

The construction of PVC matrix type tripelennamine ion selective electrodes and their use for direct potentiometry, potentiometric titration and flow injection analysis of tripelennamine cation are described. The membranes of these electrodes consist of tripelennamine-tetraphenylborate, reineckate and picrylsulfonate ion-association complexes dispersed in PVC matrix with tributyl phosphate (TBP) plasticizer. The electrodes exhibit near-Nernstian response over the concentration range of 10^–1-10^–4 M tripelennamine over the pH range 4.5–8.0. Selectivity coefficients data obtained for 17 different organic and inorganic ions are presented. The results obtained for the determination of 29 g/ml-29 mg/ml of tripelennamine with the proposed electrodes show average recoveries of 99.5–99.9% and mean standard deviations of 0.6–1.2%. The data agree well with those obtained by the standard methods.     

Plastic membrane electrodes for the potentiometric determination of codeine in pharmaceutical preparations

Four PVC membrane electrode systems responsive to codeinium cation are described. These electrodes are based on the use of the ion-association complexes of the codeinium cation with tetraphenylborate and reineckate counter-anions as ion-exchange sites in a PVC matrix plasticized with dioctylphthalate and dibutylsebacate. The performance characteristics of these electrodes reveal fast, stable and near-Nernstian responses for codeine down to concentrations of 3.5–7.0 × 10^–5 M. Over the pH range 2.5–7, the electrodes are satisfactory for manual and flow injection determination of codeine in various pharmaceutical preparations. There is negligible interference from a number of inorganic and organic cations and some common drug excipients. In the direct determination of 30 g/ml -1.0 mg/ml codeine, the average recovery is 100.6% and the mean standard deviation is ± 0.8%. The results compare favorably with those obtained by the British Pharmacopoeia method.     

Application of a Zeolite-Poly(vinyl chloride) Electrode to Potentiometric Studies of Alkali Metal Ions

Potentiometric electrodes based on the incorporation of zeolite particles into poly(vinyl chloride) (PVC) membranes are described. The electrode characteristics are evaluated regarding the response towards alkali ions. PVC membranes plasticized with dibutyl phthalate and without lipophilic additives (co-exchanger) are used throughout this study. The electrode exhibits a Nernstian response over the alkali metal cation concentration range of 1.0 × 10^?4 to 1.0 × 10^?1 M with a slope of 57.0 ± 0.9 mV per decade of concentration with a working pH range 3.0–9.0 and a fast response time of ≤15 s. The selectivity coefficients for cesium ion as test species with respect to alkaline earth, ammonium, and some heavy metal ions are determined. The proposed zeolite-PVC electrode is applied to the determination of ionic surfactant.     

New polymeric membrane cadmium(II)-selective electrodes using tripodal amine based ionophores

Fabrication of PVC membrane electrodes incorporating selective neutral carriers for Cd(2+) was reported. The ionophores were designed to have different topologies, donor atoms and lipophilicity by attaching tripodal amine (TPA) units to the lipophilic anthracene (ionophore I) and p-tert-butylcalix[4]arene (ionophores II, III and IV). The synthesized ionophores were incorporated to the plasticized PVC membranes to prepare Cd(II) ion selective electrodes (ISEs). The membrane electrodes were optimized by changing types and amounts of ionic sites and plasticizers. The selectivity of the membranes fabricated from the synthesized ionophores was evaluated, the relationship between structures of ionophores and membrane characteristics were explored. The ionophore IV which composed of two opposites TPA units on the calix[4]arene compartment showed the best selectivity toward Cd(2+). The best membrane electrode was fabricated from ionophore IV (10.2 mmol kg(-1)) with KTpClPB (50.1 mol% related to the ionophore) as an ion exchanger incorporated in the DOS plasticized PVC membrane (1:2; PVC:DOS). The Cd-ISE fabricated from ionophore IV exhibited good properties with a Nernstian response of 29.4±0.6 mV decade(-1) of activity for Cd(2+) ions and a working concentration range of 1.6×10(-6)-1.0×10(-2)M. The sensor has a fast response time of 10s and can be used for at least 1 week without any divergence in potential. The electrode can be used in the pH range of 6.0-9.0. The proposed electrodes using ionophores III and IV were employed as a probe for determining Cd(2+) from the oxidation of CdS QDs solution and the real treatment waste water sample with excellent results.     

Poly (Vinyl Chloride) Matrix Membrane Electrodes Responsive to Thiocyanate,Perchlorate and Periodate

Abstract

Three types of PVC matrix membrane ion-selective electrodes (ISEs) are described. These are based on membranes containing nitron thiocyanate with 2-nitro-phenyl phenyl ether, 2-nitrophenyl phenyl ether alone and tetraphenylarsonium thiocyanate with 2-nitrophenyl octyl ether. Each type is conditioned and stored in 0.1M sodium thiocyanate. The first two electrodes have been evaluated for thiocyanate and perchlorate response and the best linear long range (linear range down to 2.5×10^?5M) response was obtained for perchlorate. The third electrode is suitable as a periodate ISE with linear calibration range down to 2×10^?4M. The plasticized (2-nitrophenyl phenyl ether) PVC electrode for thiocyanate and perchlorate had a much longer pH interference free range (1.5–12.5) than either of the other electrodes.     

Construction and evaluation of a potassium-selective tube-mounted membrane electrode

A simple procedure for the rapid construction of inexpensive potassium-selective electrodes with valinomycin-based PVC membranes is described. Potassium-selective membranes were formed on the end of Parafilm- or Tygon-covered glass tubes by dipping the tubes into a mixture of PVC, valinomycin, and dioctyl sebacate dissolved in tetrahydrofuran. Small internal Ag/AgCl reference electrodes were made with silver wire and placed inside the tubes with AgCl-saturated potassium chloride solution. This procedure yields tube-mounted membrane electrodes that perform as well as commercially available potassium-selective electrodes in terms of their response characteristics and practical applications with soil extracts. Moreover, it facilitates the evaluation of membranes with different compositions, for making ion-selective electrodes.     

Potentiometric sensor for the high throughput determination of tetramisole hydrochloride

The electrochemical response characteristics of poly(vinyl)chloride (PVC) based membrane sensors for determination of tetramisole hydrochloride (TmCl) is described. The membranes of these electrodes consist of tetramisole-tetraphenyl borate (Tm-TPB), chlorophenyl borate (Tm-ClPB), and phosphotungstate (Tm(3)-PT) ion associations dispersed in a PVC matrix with dibutylpthalate as a plasticizer. The electrodes were fully characterized in terms of composition, life span, usable pH range, and working concentration range and ionic strength. The electrodes showed Nernstian response over the concentration ranges of 7.4 x 10(-7) to 1.0 x 10(-2) M, 1.7 x 10(-6) to 1.0 x 10(-2) M, and 5.6 x 10(-6) to 1.0 x 10(-2) M TmCl, respectively, and were applied to the potentiometric determination of tetramisole ion in pure solutions and pharmaceutical preparations. The potentiometric determination was also used in the determination of tetramisole in pharmaceutical preparations in four batches of different expiration dates. The electrodes exhibited good selectivity for TmCl with respect to a large number of excipients such as inorganic cations, organic cations, amino acids, and sugars. The solubility product of the ion-pair and the formation constant of the precipitation reaction leading to the ion-pair formation were determined conductometrically. The new potentiometric method offers the advantages of high-throughput determination, simplicity, accuracy, automation feasibility, and applicability to turbid and colored sample solutions.     

Potentiometric flow injection analysis of dicyclomine hydrochloride in serum, urine and milk

Five plastic membrane electrodes for the determination of dicyclomine hydrochloride (DcCl) were fabricated and fully characterized in terms of composition, life span, usable pH range, working concentration range and temperature. The membranes of these electrodes consist of dicyclominium-silicotungstate (Dc-ST), silicomolybdate (Dc-SM), phosphotungstate (Dc-PT), phosphomolybdate (Dc-PM) or tetraphenylborate (Dc-TPB) ion-associations dispersed in PVC matrix with dibutyl phthalate plasticizer. The electrodes showed near-Nernstian response over the concentration range of 4.0 × 10⁻⁶ to 1.0 × 10⁻² M DcCl and applied to the potentiometric determination of dicyclominium ion in pharmaceutical preparations, serum, urine and milk in batch and flow injection (FI) conditions with average recoveries of 96.1-102.7% and relative standard deviation of 0.055-1.994%. The electrodes exhibit good selectivity for DcCl with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The sensitivities of these electrodes are high enough to measure as low as 1.73 μg/ml of DcCl which permit the determination of the K_sp values of the ion-associates used. The proposed potentiometric methods offer the advantages of simplicity, accuracy, automation feasibility and applicability to turbid and colored sample solutions.     

Optimization of polymeric triiodide membrane electrode based on clozapine-triiodide ion-pair using experimental design

Central composite design (CCD) and response surface methodology (RSM) were developed as experimental strategies for modeling and optimization of the influence of some variables on the performance of a new PVC membrane triiodide ion-selective electrode. This triiodide sensor is based on triiodide-clozapine ion-pair complexation. PVC, plasticizers, ion-pair amounts and pH were investigated as four variables to build a model to achieve the best Nernstian slope (59.9 mV) as response. The electrode is prepared by incorporating the ion-exchanger in PVC matrix plasticized with 2-nitrophenyl octal ether, which is directly coated on the surface of a graphite electrode. The influence of foreign ions on the electrode performance was also investigated. The optimized membranes demonstrate Nernstian response for triiodide ions over a wide linear range from 5.0 x 10(-6) to 1.0 x 10(-2)mol L(-1) with a limit of detection 2.0 x 10(-6) mol L(-1) at 25 degrees C. The electrodes could be used over a wide pH range 4-8, and have the advantages of easy to prepare, good selectivity and fast response time, long lifetime (over 3 months) and small interferences from hydrogen ion. The proposed electrode was successfully used as indicator electrode in potentiometric titration of triiodide ions and ascorbic acid.     

Papaverine PVC membrane ion-selective electrodes based on its ion-exchangers with tetraphenylborate and tetrathiocyanate anions

The construction and general performance of novel potentiometric membrane ion selective electrodes for determination of papaverine hydrochloride has been described. They are based on the formation of the ion association complexes of papaverine (PA) with tetraphenylborate (TPB)(I) or tetrathiocyanate (TTC)(II) counter anions as electro-active material dispersed in a PVC matrix. The electrodes show fast, stable, near Nernstian response for 1 x 10(-2) to 6 x 10(-5) M and 1 x 10(-2) to 1 x 10(-5) M for PA-TPB and PA-TTC respectively at 25 degrees C over the pH range of 3-5.0 with a cationic slope of approximately 56.5 +/- 0.5 mV/decade for both sensors respectively. The lower detection limit is 4 x 10(-5) and 8 x 10(-6) M for PA- I and PA-II respectively with fast response time ranging from 20-45 sec. Selectivity coefficients for PA relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of 4.0- 3000.0 microg/ml of PA in aqueous solutions shows an average recovery of 99.1% and a mean relative standard deviation of 1.4 at 100microg/ml. The direct determination of PA in some formulations (Vasorin injection) gave results that compare favorably with those obtained using the British Pharmacopoeia method. Potentiometric titration of PA with sodium tetraphenylborate and potassium thiocyanate as titrants utilizing the papaverine electrode as an end point indicator electrode has been carried out.     

Spectrophotometric determination of vitamin E (alpha-tocopherol) using copper(II)-neocuproine reagent

A coated graphite-epoxy ion-selective electrode for bismuth(III), based on the ion-pair between the [Bi(EDTA)](-) anion and tricaprylylmethylammonium cation (Aliquat 336S) incorporated onto a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) or ortho-nitrophenyloctylether (o-NPOE) in PVC was deposited directly onto a Perspex(R) tube which contained a graphite-epoxy conductor substrate attached to the end of a glass tube. The coating solution was prepared by dissolving 30% (w/w) of PVC in 10 ml of tetrahydrofuran following addition of 65% (w/w) DBPh or o-NPOE and 5% (w/w) of the ionic pair. The effect of pH, EDTA concentration and some cation and anion on the electrode response is investigated. The bismuth(III) ion-selective electrode shows a linear response in the bismuth(III) concentration range from 1.0 x 10(-8) to 1.0 x 10(-1) mol 1(-1) and 1.0 x 10(-7) to 1.0 x 10(-1) mol 1(-1) and a slope of 56.8 and 59.2 mV dec.(-1) for the polymeric membranes containing DBPh and o-NPOE, respectively. The lifetime of this electrode was superior to 1 year (over 1600 determinations for each polymeric membrane), with practical detection limits of 6.3 x 10(-9) and 4.4 x 10(-8) mol 1(-1) with these plasticizers. Application of this electrode with bismuth(III) determination in a stomach anti-acid sample is described.     

Salicylate-Selective PVC Membrane Electrodes Based on Tribenzyltin(IV) Phenolates as Neutral Carriers

ABSTRACT

A series of tribenzyltin(IV) phenolates were synthesized and used as anion ionophores for PVC membrane electrodes; these novel electrodes exhibit a linear response towards salicylate and an anti-Hofmeister selectivity pattern with high specificity for salicylate over many common anions. The results show that the behavior of the electrodes is considerably influenced by the structures of the carriers and the experimental conditions. Electrodes based on tribenzyltin(IV) p-nitrophenolate possess the best potentiometnc response characteristics and show a linear log[Sal^?] vs. EMF response over the concentration range 0.1–3.98×10^?6 mol.L^?1 in phosphate buffer solutions of pH 5.38 with a detection limit of 2.51×10^?6 mol.L^?1 and a slope of -57.05 mV per decade. The response mechanism was also investigated by use of a.c. impedance and anion transport across liquid membranes. The electrodes were applied to the determination of salicylate in urine samples with satisfactory results.     

Some alkylphosphoric acid esters for use in coated-wire calcium-selective electrodes: Part I. Response characteristics

The use of several alkylphosphoric acid esters in the production of PVC membranes for use as calcium-sensitive, coated-wire electrodes is reported. The response characteristics, reproducibility, region of linear response for, and effect of plasticizer on, the electrodes are discussed.     

Tetracycline Potentiometric Sensor Based on Cyclodextrin for Pharmaceuticals and Waste Water Analysis

In this work, the construction and performance evaluation of PVC membranes ion‐selective electrodes for the determination of tetracycline type antibiotics is described. Electrodes with the best responses were based on plastic membranes containing 31% (w/w) PVC, 68% (w/w) of dibutylphthalate as plasticizer and 1% (w/w) of β‐cyclodextrin as ionophore. The electrodes were responsive over 6 months to tetracycline, oxytetracycline, doxycycline and chlortetracycline in glycine buffer solution (pH 2), in the dynamic range 2×10^?5–10^?2 mol L^?1 with a constant slope of about 55 mV/dec To enable large scale analysis reducing wastes as associated costs tubular shape electrodes were coupled to a sequential‐injection analysis system and its performance evaluated using pharmaceutical samples and waste waters from a treatment facility. The sample throughput of 51 samples h^?1 was enabled by the system as well as results that favorably agree with those provided by chromatographic analysis.     

Malachite green as a reagent for detection and spectrophotometric determination of chromium(VI)

A sensitive and inexpensive method of spectrophotometric determination of chromium(VI), based on the absorbance of its complex with malachite green and acetic acid at pH 2.5 is reported. The complex shows a molar absorptivity of 8 x 10(4) l.mole(-1) cm(-1) at 560 nm, using malachite green and acetic acid as reference solution. The effect of time, temperature, pH and reagent concentration is studied and optimum operating conditions are established. Beer's law is applicable in the concentration range 2.0-22.8 mug/ml chromium(VI). The resin beads act as a catalyst and as little as 1.6 mug of chromium(VI) is detected in the resin phase as compared to 4.1 mug in the solution phase. The standard deviation in the determinations is +/-0.40 mug/ml for a 10.35 mug/ml solution.     

Novel Poly(ethylene glycol)s Bearing Tributyltin Carboxylate End Groups as Ionophores in the Development of Chloride Ion‐Selective Electrodes

The potentiometric response characteristics of electrodes based on PVC membranes containing novel polyethylene glycols (PEGs) with tributyltin carboxylate end groups as ionophores for chloride ions were studied in 0.1 M HEPES solution, at the spontaneous pH. The effects of solvent mediator, amount of cationic additive, amount of ionophore and PEG chain length on the behavior of the sensors were investigated. The membranes with the best composition responded to chloride concentration in a linear range from 10^?4 to 10^?1 M Cl^? with a nearly Nernstian slope and a detection limit of 6.5×10^?5 M. The sensor showed a short response time (<25 s) in the whole concentration range and an operational lifetime of about one week for the most performing PVC membranes. In comparison with ISEs based on anion exchangers the interferences from the more lipophilic anions were greatly reduced, as inferable by the selectivity coefficients determined with the matched potential method at chloride concentration of 3.0×10^?3 M.