Fabrication of an ion-selective electrode for determination of propylhexedrine

Electrodes of both conventional and micro-sizes were based on the use of propylhexedrine-reineckate as the ion-exchanger in a plastic membrane. The electrodes exhibited Nernstian response towards propylhexedrine (PX) over the concentration range 10^–6–10^–2 M and had life spans of up to 2 days continuous work. The working pH range was 2.3–8. Investigation of diverseions reveals good selectivity for propylhexedrine over several inorganic cations, amines, aminoacids, sugars and some pharmaceutical compounds. The electrode was applied for determination of the drug in urine with 99.1% recovery and 0.15–0.31% relative standard deviation.     

Effect of Plasticizer on the Performance of the Surfactant-Selective Electrode Based on a Poly(Vinyl Chloride) Membrane with no Added Ion-Exchanger

The effect of different plasticizers in the sensing membrane on the performance of a surfactant ISE based on a PVC membrane with no added ion-exchanger was investigated. o-nitrophenyl octyl ether (NPOE), o-nitrophenyl decyl ether (NPDE), o-nitrophenyl dodecyl ether (NPDOE) and o-nitrophenyl tetradecyl ether (NPTE) were used as plasticizers. Electrodes based on NPDE, NPDOE and NPTE produced better results than NPOE-plasticized PVC membrane electrodes in terms of low detection limits. Electrodes based on NPDE, NPDOE and NPTE displayed a Nernstian slope in the concentration range of 10^–6 to 10^–2M. NPOE-plasticized PVC membrane electrodes displayed a Nernstian slope in the concentration range of 10^–5 to 10^–2M. The three electrodes other than the NPOE-plasticized PVC membrane electrode showed a similar performance to that of the NPOE-plasticized PVC membrane electrode concerning low detection limits and slope sensitivity. The four electrodes examined in this study are excellently selective for the dodecyltrimethylammonium ion over inorganic anions, but interference from other cationic surfactants such as tetradecyltrimethylammonium ions is significant. With respect to slope sensitivity, selectivity, response time and pH effect, the four electrodes showed a similar performance.     

Nucleophilic substitution in the 10,11-dihydrodibenz[b,f]iodepinium cation

10,11-Dihydrodibenz[b,f]iodepinium tetrafluoroborate gave only 1-(2-azidophenyl)-2-(2-iodophenylethane with the N₃ ^– in aqueous DMSO, while with NO₂ ^– it gave 1-(2-nitrophenyl)-2-(2-iodophenyl)ethane (93%), 9,10-dihydrophenanthrene (5%), and traces of phenanthrene. Both in pure and aqueous DMSO this cation with the Br^– ion was converted into phenanthrene (80% and 68% respectively) and 1-(2-bromophenyl)-2-(2-iodophenyl)ethane (10 and 20%), while in water it gave 9,10-dihydrophenanthrene (75%) and phenanthrene (5%). A new route for the synthesis of 1-(2-aminophenyl)-2-phenylethane starting from this tetrafluoroborate has been proposed.M. V. Lomonosov Moscow State University, Moscow 119899, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, 110–115, January, 1999.     

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.     

Effect of using mixed ion-pairs on PVC-membrane electrodes for ephedrine

Mixed ion-pairs based on the use of ephedrinium (EPH)-TPB plus EPH-reineckate (II) and phenylephrine-TPB plus EPH-reineckate (III) were tried for use in plastic membranes. The results were compared to those of an EPH-reineckate (I) single ion-pair electrode. The Nernstian slopes were 50, 49 and 55 mV decade^–1 for membranes I, II and III, respectively. The linear concentration ranges were 10^–5–10^–1, 4.0 × 10^–5–10^–1 and 6.3 ×^–5–10^–1 M ephedrine. The detection limits were 4 ×^–6,10^–5 and 1.2 × 10^–5 M ephedrine for membranes I, II and III, respectively. The pH ranges were 4–9, 3–9 and 2–8 for I, II and III-membranes, respectively. Selectivity coefficient values for membrane II were better than those for membranes I and III. The effects of increasing KC1 concentration and temperature changes were explained for the three electrodes. The isothermal temperature coefficients were 0.00145, 0.0007 and 0.00055 V/ °C for electrodes I, II and III. Electrode III was applied for the determination of ephedrine in its pharmeaceutical preparations with an overall relative standard deviation range of 1.3–2.4% and an overall mean recovery value of 98.1%.     

Nucleophilic substitution in dibenz[b,d]iodolium and 11,12-dihydro-10H-dibenz[b,g]iodocinium cations

Treatment of dibenz[b,d]iodolium tetrafluoroborate with NO₂ ^–, Br^–, and N₃ ^– ions gave, along with nucleophilic substitution products, 2-nitro-, 2-bromo-, and 2-azido-2-iodiphenyls, diphenyl, 2-iododiphenyl, and 2,2-diiododiphenyl (products of one electron reduction), whereas 11,12-dihydro-10H-dibenz[b,g]iodocinium tetrafluoroborate underwent nucleophilic substitution with all three nucleophiles to give a single product in each case: 1-(2-nitrophenyl)-, 1-(2-bromophenyl)-, or 1-(2-azidophenyl)-3-(2-iodophenyl)propane.M. V. Lomonosov Moscow State University, Moscow 119899. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 405–412, March, 1998.     

A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques

A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10^–5–1.0×10^–1 M and 6.0×10^–6–1.0×10^–1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10^–6 and 6.0×10^–6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu²⁺ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu²⁺ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.     

A comparison of different types of gold–carbon composite electrode for detection of arsenic(III)

A study has been conducted using abrasively modified basal and edge-plane graphite, carbon-paste, and carbon–epoxy electrodes to create gold–carbon composite electrodes. Using either nano or micro-sized gold particles their suitability for use in detecting arsenic(III) is assessed. It was found that gold arrays prepared from micron-sized particles gave the best performance for arsenic detection. In particular micron arrays produced in carbon-paste electrodes with an easily renewable surface work well for detection of arsenic, producing a detection limit of 5(±2)×10^–9 mol L^–1, with a high sensitivity of 10(±0.1) A mol^–1 L.     

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 molybdophosphate and tungstophosphate counter anions as ion pairs in a plasticized PVC matrix. The electrodes show a stable, near-Nernstian response for 6 × 10^–5–1 × 10^–2 M VB₆ at 25°C over the pH range 2–4 with a cationic slope of 54.0 ± 0.5 and 54.5 ± 0.4 mV per concentration decade for pyridoxine–molybdophosphate and pyridoxine–tungstophosphate, respectively. The two electrodes have the same lower detection limit (4 × 10^–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. 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 = 3) for pyridoxine–molybdophosphate and pyridoxine–tungstophosphate electrodes, respectively. The results compare favorably with data obtained by the British pharmacopoeia method.     

A propranolol-responsive coated-wire electrode

Propranolol-responsive electrodes of both the coated wire and conventional types based on the didodecylnaphthalene sulfonic acid salt were prepared and their operating characteristics were compared. The detection limit of the coated-wire electrodes is about 10^-6 M; interferences from common inorganic ions and from the analagous product isoproterenol are small. The response time varies from 15 s to 30 min depending on concentration; readings are reproducible to within 0.5 mV. Electrodes are still operational after six months of intermittent use.     

Primary amine drug sensitive electrodes based on macrocyclic polyethers with 2,2′-dinaphthyl subunits

Dinaphthyl macrocyclic polyethers were synthesized and used as neutral carriers for preparing primary amine drug sensitive PVC membrane electrodes. Contrary to the ion-associate based electrodes, which show an excellent potentiometric response to quaternary ammonium ions and the like, but a very poor response to primary amines, the macrocyclic polyether-based electrodes showed potentiometric response characteristics with primary amines preferred. Dinaphthyl macrocyclic polyether-based electrodes are superior to those based on common macrocyclic polyethers for their potentiometric selectivity coefficients much lower than those of the latter. The main characteristics of a dinaphthyl-20-crown-6-based benzyl amine sensitive electrode are as follows: linear response range, 4.2 × 10^–5 – 1.0 ×10^–1 M; slope, 51.3 mV/decade; and detection limit, 4.6 × 10^–6 M. A mexiletine sensitive electrode was prepared using dinaphthyl-23-crown-7 with following performance features: linear response range, 2.0 × 10^–5 – 1.0 ×10^–1 M; slope, 52.1mV/decade; and detection limit, 5.0 × 10^–6 M.     

Benzoate ion-selective electrode with improved selectivity and reproducibility for benzoate determination in medicinal syrups

This paper describes the construction and evaluation of a benzoate anion selective electrode with enhanced working characteristics, namely reproducibility and selectivity, to be used in medicinal syrups analysis by direct potentiometry. The electrode, without an internal reference solution, was prepared with a PVC membrane, based onbis(triphenylphosphoranylidene) ammonium benzoate as ion-exchanger, dissolved in 2-nitrophenyl octyl ether as mediator solvent and 4-t-octylphenol as additive. The characteristics of the electrodes were evaluated in sodium benzoate solutions with adjusted ionic strength and showed a linear response in the range 10^–2–2 × 10^–4 mol dm^–3 with a slope of 54.7 ± 0.5 mV/decade and a reproducibility of ±0.2 mV/day for solutions with pH 6.3. The potentiometric selectivity coefficients were determined for some possible interfering species and showed that the electrodes prepared with the additive had good selectivity, especially over iodide and nitrate, when compared with those without any additive. The electrodes were used for benzoate determinations in several medicinal syrups by direct potentiometry. The results gave recovery values in the range 98.3–104.6%.     

Mercury-free sono-electroanalytical detection of lead in human blood by use of bismuth-film-modified boron-doped diamond electrodes

We report the electroanalytical determination of lead by anodic stripping voltammetry at in-situ-formed, bismuth-film-modified, boron-doped diamond electrodes. Detection limits in 0.1 mol L^–1 nitric acid solution of 9.6x10^–8 mol L^–1 (0.2 ppb) and 1.1x10^–8 mol L^–1 (2.3 ppb) were obtained after 60 and 300 s deposition times, respectively. An acoustically assisted deposition procedure was also investigated and found to result in improved limits of detection of 2.6×10^–8 mol L^–1 (5.4 ppb) and 8.5×10^–10 mol L^–1 (0.18 ppb) for 60 and 300 s accumulation times, respectively. Furthermore, the sensitivity obtained under quiescent and insonated conditions increased from 5.5 (quiescent) to 76.7 A mol^–1 L (insonated) for 60 s accumulation and from 25.8 (quiescent) to 317.6 A mol^–1 L (insonated) for 300 s accumulation. Investigation of the use of ultrasound with diluted blood revealed detection limits of the order of 10^–8 mol L^–1 were achievable with excellent inter- and intra-reproducibility and sensitivity of 411.9 A mol^–1 L . For the first time, electroanalytical detection of lead in diluted blood is shown to be possible by use of insonated in-situ-formed bismuth-film-modified boron-doped diamond electrodes. This method is a rapid, sensitive, and non-toxic means of clinical sensing of lead in whole human blood.     

Reproterol plastic membrane ion-selective electrodes based on its individual and mixed ion-exchangers with phosphotungstic and/or phosphomolybdic acids

Reproterol hydrochloride (RpCl), selective PVC membranes based on ion associates of reproterolium-phosphotungstate (Rp-PTA); reproterolium-phospho-molybdate (Rp-PMA) or a mixture of both (Rp-PTA/PMA) were prepared. The electrodes displayed a linear response over the concentration range of 6.3×10⁻⁶–1.0×10⁻¹ mol dm⁻³ RpCl. The working pH ranges of the above electrodes were 2.5–9.0, 2.5–8.5 and 2.0–9.0 and their isothermal temperature coefficients were 0.00014, 0.00090 and 0.00103 V/°C, respectively. The electrodes showed good selectivity to the reproterolium ion with respect to many inorganic cations, sugars and amino acids. The standard additions and potentiometric titration methods were used to determine RpCl in pure solutions and in its pharmaceutical preparations with high accuracy and precision.     

Cholinesterase sensors based on screen-printed electrodes for detection of organophosphorus and carbamic pesticides

Cholinesterase sensors based on screen-printed electrodes modified with polyaniline, 7,7,8,8-tetracyanoquinodimethane (TCNQ), and Prussian blue have been developed and tested for detection of anticholinesterase pesticides in aqueous solution and in spiked grape juice. The influence of enzyme source and detection mode on biosensor performance was explored. It was shown that modification of the electrodes results in significant improvement of their analytical characteristics for pesticide determination. Thus, the slopes of the calibration curves obtained with modified electrodes were increased twofold and the detection limits of the pesticides were reduced by factors of 1.6 to 1.8 in comparison with the use of unmodified transducers. The biosensors developed make it possible to detect down to 2×10^–8 mol L^–1 chloropyrifos-methyl, 5×10^–8 mol L^–1 coumaphos, and 8×10^–9 mol L^–1 carbofuran in aqueous solution and grape juice. The optimal conditions for grape juice pretreatment were determined to diminish interference from the sample matrix.Abbreviations ChE Cholinesterase - TCNQ 7,7,8,8-Tetracyanoquinodimethane - ChO Choline oxidase - AChE Acetylcholinesterase - BChE Butyrylcholinesterase - BSA Bovine serum albumin - 2-PAM 2-Pyridine aldoxime methiodide     

Dynamic quartz crystal impedance measurements of polyvinylferrocene film deposition

Dynamic crystal impedance measurements were used to study the electrochemically-driven deposition of polyvinylferrocene (PVF) films from dichloromethane solutions of PVF onto Au electrodes of a quartz crystal microbalance. Under all the conditions studied, the PVF films were non-rigid, to an extent that depended upon several experimental factors. Films deposited from solutions containing perchlorate salts of tetraalkylammonium salts departed less from rigidity than those deposited under otherwise identical conditions from tetrafluoroborate media. In contrast, the use of different tetraalkylammonium cations, or the use of a potential sweep vs. a potential step from 0 V to the deposition potential (0.7 V), made no significant difference. The departure from rigid characteristics varied with coverage. For the interval of time during deposition that the coverage was 10–160 nmol cm⁻² (of monomeric ferrocene units), the films showed no additional departure from rigidity. On the basis that the upper figure corresponds closely to a “monolayer” of terminally attached chains of mean length, we attribute this behaviour to the presence of a dense film, within which chain motion is considerably restrained.     

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.     

Electrochemical Preconcentration of Arsenic(III) in Its Determination by Stripping Voltammetry at Graphite Electrodes Modified with Gold and Copper

The effect of some factors (potential and time of electrolysis, nature and concentration of supporting electrolyte) on the electrochemical preconcentration of arsenic at graphite electrodes modified with copper and gold adatoms was studied. The data obtained were used for the determination of 10^–7to 10^–6M arsenic(III) by stripping voltammetry. The detection limits for arsenic using graphite electrodes modified with copper and gold were 6.3 × 10^–7and 2.3 × 10^–7M, respectively.     

Cyclic voltammetric study of the catalytic behavior of nickel(I) salen electrogenerated at a glassy carbon electrode in an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIMBF4)

Cyclic voltammetry has been employed to examine the electrochemistry of nickel(II) salen at a glassy carbon electrode in an ionic liquid (1-butyl-3-methylimidazolium tetrafluoroborate, BMIM⁺BF₄⁻). Residual water in the ionic liquid can be eliminated by introduction of activated molecular sieves into the electrochemical cell. Nickel(II) salen exhibits a one-electron, quasi-reversible reduction to nickel(I) salen, and the latter species serves as a catalyst for the cleavage of carbon–halogen bonds in iodoethane and 1,1,2-trichlorotrifluoroethane (Freon^® 113). In BMIM⁺BF₄⁻ the diffusion coefficient for nickel(II) salen at room temperature has been determined to be 1.8×10⁻⁸ cm² s⁻¹, which is more than 500 times smaller than that (1.0×10⁻⁵ cm² s⁻¹) in a typical organic solvent–electrolyte system such as dimethylformamide (DMF) containing 0.10 M tetramethylammonium tetrafluoroborate.     

An Amperometric Biosensor Based on Laccase Immobilized in Polymer Matrices for Determining Phenolic Compounds

An amperometric enzyme electrode based on laccase for determining phenolic compounds is proposed. The following three types of polymer materials were used for enzyme immobilization on the surface of a glassy-carbon electrode: positively charged cetyl ethyl poly(ethyleneimine) (CEPEI) and negatively charged commercial Nafion and Eastman AQ 29D polymers. The advantages and disadvantages of each of the above polymers for enzyme immobilization are discussed. The detection limits of the model phenolic compounds hydroquinone and pyrocatechol in a buffer solution on laccase immobilization in a Nafion membrane were 3.5 × 10⁻⁸ and 5.0 × 10⁻⁸ M, respectively, at a signal-to-noise ratio of 3. Electrodes with laccase immobilized in Nafion and Eastman AQ 29D membranes exhibited the shortest response time. The operating stability and the stability in storage can be significantly improved by the additional incorporation of gelatin in the polymer matrices. Gelatin prevents enzyme inactivation as a result of enzyme modification by the free-radical oxidation products of phenolic compounds.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 624–628.Original Russian Text Copyright © 2005 by Yaropolov, Shleev, Morozova, Zaitseva, Marko-Varga, Emneus, Gorton.Presented at the VI All-Russia Conference (with international participation) on Electrochemical Methods of Analysis (EMA-2004, Ufa, May 23–27, 2004).