Novel sulfate ion-selective polymeric membrane electrode based on a derivative of pyrilium perchlorate

A sulfate ion-selective PVC membrane sensor based on 4-(4-bromophenyl)-2,6-diphenylpyrilium perchlorate (BDPP) as a novel sensing material is successfully developed. The electrode shows a good selectivity for sulfate ion with respect to common organic and inorganic anions. The sensor exhibits a good linear response with slope of -28.9+/-0.5 mV per decade over the concentration range of 1.0x10(-6)-1.0x10(-2) M, and a detection limit of 8.0x10(-7) M of SO(4)(2-) ions. The electrode response is independent of pH in the range of 4.0-9.0. The proposed sensor was applied as an indicator electrode in potentiometric titration of sulfate and barium ions, and to the determination of zinc in zinc sulfate tablets.     

A new liquid membrane electrode for the selective determination of perrhenate

A new perrhenate ion-selective electrode has been developed, incorporating a nitrobenzene solution of nitron perrhenate as a liquid membrane. The electrode gives near-Nernstian response to 3 x 10(-5)-10(-2)M perrhenate over the pH range 3-8. Most common anions (except for periodate and perchlorate) give little interference. The electrode has been satisfactory for direct potentiometric determination of as little as 10 mu/ml rhenium. The average recovery and standard deviation were 99% and 2.1%, respectively. Measurements of the solubility products of some sparingly soluble perrhenates gave results that agreed closely with those recorded in the literature and obtained by other procedures.     

PVC membrane ion selective electrode for the determination of pentachlorophenol in water, wood and soil using tetrazolium pentachlorophenolate

A novel PVC membrane electrode selective for the determination of pentachlorophenolate (PCP) ion based on 2,3,5-triphenyl-2H-tetrazolium (TPT) pentachlorophenolate ion pair as an electroactive material is described. The electrode shows a linear response for PCP ion over the concentration range of 6x10(-5) to 1x10(-2) M with lower detection limit of 4x10(-5) M at 25 degrees C. The electrode posses a Nernstian slope of -55.0+/-1.0 mV/decade and a fast potential response of 45 s, which is almost constant over a pH range of 5.5-10.5. Selectivity coefficient data for some common ions show negligible interference, however, 2,4,6-trichlorophenolate and cetylpyridinium ions interfere. An average recovery of 96.2% with relative standard deviation of 2.3% has been achieved for the determination of 75.0 ppm PCP in wastewater samples. The determination of PCP in soil and wood samples gave results that compare favorably with those obtained by gas chromatography. The electrode has been utilized as an end point indicator electrode for the determination of PCP using potentiometric titration.     

Uranyl-selective PVC membrane electrodes based on some recently synthesized benzo-substituted macrocyclic diamides

Four different recently synthesized macrocyclic diamides were studied to characterize their abilities as uranyl ion carriers in PVC membrane electrodes. The electrodes based on macrocycle 1,18-diaza-3,4;15,16-dibenzo-5,8,11,14,21,24-hexaoxacyclohexaeicosane-2,17-dione resulted in a Nernstian response for UO(2)(2+) ion over wide concentration ranges. The linear concentration range for the polymeric membrane electrode (PME) is 3.0x10(-6)-8.2x10(-3) M with a detection limit of 2.2x10(-6) and that for the coated graphite electrode (CGE) is 5.0x10(-7)-1.5x10(-3) M with a detection limit of 3.5x10(-7) M. The electrodes manifest advantages of low resistance, very fast response and, most importantly, good selectivities relative to a wide variety of other cations.     

Potentiometric batch and flow injection analysis of betaine hydrochloride

Novel PVC membrane electrodes for the determination of betaine ion based on the formation of betaine-tetraphenylborate (Be-TPB) and betaine-phosphotungstate (Be-PT) ion-exchangers as electroactive materials are described. The sensors show a fast, stable, near Nernstian response for 6.92 x 10(-6) to 7.94 x 10(-3) M and 1.0 x 10(-4) to 1.0 x 10(-2) M betaine hydrochloride (Be.Cl) in case of Be-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 2.95 x 10(-5) to 2.26 x 10(-3) M and 3.16 x 10(-5) to 1.0 x 10(-2) M in case of Be-PT electrode for batch and FIA electrodes, respectively, at 25 degrees C over the pH range of 3.5-10 with a cationic slope of 60.2 and 59.1 mV decade(-1) and a fast potential response of < or =15 s. The lower detection limits are 7.94 x 10(-6) and 3.18 x 10(-5) M Be.Cl for Be-TPB and Be-PT electrodes, respectively. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components other than betaine, of the mixed drug investigated show negligible interference. The electrodes have been applied to the direct potentiometric determination of betaine hydrochloride in water and in a pharmaceutical preparation under batch and FIA conditions. Potentiometric titrations of Be.Cl with NaTPB and PTA as titrants were monitored with the developed betaine electrodes as an end point indicator electrode. The determination of Be.Cl shows an average recovery of 100.8% with mean relative standard deviation of 0.61%. The effect of temperature on the electrodes was also studied.     

Construction of a New Perbromate-Selective Electrode. Kinetic Study of the Iron(II)- Perbromate Reaction and Microdetermination of Iron

Abstract

A perbromate- selective membrane electrode with a liquid membrane of crystal violet-perbromate dissolved in chlorobenzene is described, The liquid membrane electrode exhibits rapid and near Nernstian response to perbromate activity from 10^?5 to 10^?2 M. The response is unaffected by pH in the range 2–10, Major interferences are periodate and perchlorate. A kinetic study of the iron(II)- perbromate reaction was carried out with the perbromate electrode, A potentiometric method is described for the determination of 50–500 μg of iron (II) with relative errors and standard deviations of 1–2%.     

A new macrocyclic polystyrene-based sensor for chromium (III) ions

A new tetradentate dihydrogen perchlorate macrocyclic ligand (2,4,9,11-tetraphenyl-1,5,8,12-tetraazacyclotetradeca-1,4,8,11-tetraene dihydrogen perchlorate) was prepared and characterised. The macrocycle behaves as a selective chelating ion-exchanger for some metal ions. The polystyrene-based membrane electrode is found to exhibit quite promising selectivity for Cr3+ ions. It can be used to estimate chromium concentrations in the range 3.16x 10(-6)-1.00x10(-1) M with a near-Nernstian slope of 17.5 mV per decade of concentration between pH 3.0 to 6.5. The electrode is found to possess a fast response time of 15 s and was used over a period of three months with good reproducibility (s = +/- 0.3 mV). The selectivity coefficient values for mono-, di- and trivalent cations indicate excellent selectivity for Cr3+ ions over a large number of other cations. Anions such as Cl- and SO4(2-) do not interfere and the electrode also works satisfactorily in a mixed organic-water solution. The sensor has been used as an indicator electrode for the potentiometric titration of Cr3+ with EDTA. The practical utility of the membrane sensor has also been demonstrated in solutions contaminated with detergents (CTAB and SDS). Above all, the membrane sensor has been very successfully used to determine Cr3+ in some foods.     

Chemically modified carbon paste electrode for iodide determination on the basis of cetyltrimethylammonium iodide ion-pair.

A new carbon paste electrode (CPE) for the determination of iodide ion based on a cetyltrimethylammonium iodide (CTMAI) ion pair as an electroactive material is described. The electrode shows a linear response for iodide ion over the concentration range of 4 x 10(-5) M to 1 x 10(-1) M with a lower detection limit of 4 x 10(-5) M at 25 degrees C. The electrode has a Nemstian slope of -55.0 +/- 0.4 mV/decade and a fast potential response of 45 s, which is almost constant over a pH range of 5.0 - 9.0. Selectivity coefficient data of the CTMAI-CPE for some common ions show negligible interference, and the electrode has high selectivity towards the iodide ion. An average recovery of 101.83% with a relative standard deviation of 1.53% has been achieved for the determination of iodide in Flaxedil (gallamine triethiodide) ampoules, a muscle relaxant drug. The electrode has been examined for the determination of iodide in saline water; the results were found to compare favorably with those obtained using Metrohm iodide ISE. The electrode has been utilized as an end-point indicator electrode for the determination of Hg(II) and phenylmercury(I) in their aqueous solutions using potentiometric titration with a potassium iodide standard solution.     

Adsorptive stripping voltammetric measurements of trace levels of uranium following chelation with mordant blue 9

The chelate of uranium with the azo dye Mordant Blue 9 is shown to be adsorbed and then reduced on the hanging mercury drop electrode. These properties have been exploited in developing a highly sensitive stripping voltammetric procedure for trace determination of uranium. With controlled adsorptive accumulation for 5 min, a detection limit near 2 x 10(-10)M uranium is obtained. Cyclic voltammetry has been used to characterize the interfacial and redox behaviour. The effect of various operational parameters on the stripping response is discussed. Experimental conditions include use of 1 x 10(-6)M Mordant Blue 9 in 0.05M acetate buffer (pH 6.5), an accumulation potential of -0.43 V, and a linear potential scan. The response is linear up to 1.2 x 10(-7)M uranium, and the relative standard deviation at 4.2 x 10(-8)M is 3.2%. The effects of possible interferences from organic surfactants or metal ions have been investigated.     

Ion-selective electrodes for potentiometric determination of ranitidine hydrochloride, applying batch and flow injection analysis techniques.

New ranitidine hydrochloride (RaCl)-selective electrodes of the conventional polymer membrane type are described. They are based on incorporation of ranitidine-tetraphenylborate (Ra-TPB) ion-pair or ranitidine-phosphotungstate (RaPT) ion-associate in a poly(vinyl chloride) (PVC) membrane plasticized with dioctylphthalate (DOP) or dibutylphthalate (DBP). The electrodes are fully characterized in terms of the membrane composition, solution temperature, and pH. The sensors showed fast and stable responses. Nernstian response was found over the concentration range of 2.0 x 10(-5) M to 1.0 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-TPB electrode and over the range of 1.03 x 10(-5) M to 1.00 x 10(-2) M and 1.0 x 10(-5) M to 1.0 x 10(-2) M in the case of Ra-PT electrode for batch and FIA systems, respectively. The electrodes exhibit good selectivity for RaCl with respect to a large number of common ions, sugars, amino acids, and components other than ranitidine hydrochloride of the investigated mixed drugs. The electrodes have been applied to the potentiometric determination of RaCl in pure solutions and in pharmaceutical preparations under batch and flow injection conditions with a lower detection limit of 1.26 x 10(-5) M and 5.62 x 10(-6) M at 25 +/- 1 degrees C. An average recovery of 100.91% and 100.42% with a relative standard deviation of 0.72% and 0.53% has been achieved.     

Highly selective PVC-membrane electrodes based on Co(II)-Salen for determination of nitrite ion.

A cobalt(II) derivative was used as a suitable ionophore for the preparation of a polymeric membrane nitrite-selective electrode. The electrode reveals a Nemstian behavior over a very wide NO2- ion concentration range (1.0 x 10(-6)-1.0 x 10(-1) M) and a very low detection limit (5.0 x 10(-7) M). The potentiometric response is independent of the pH of solution in the pH range 4.0-9.5. The electrode shows advantages such as low resistance, fast response and, most importantly, good selectivity relative to a wide variety of inorganic and organic anions. In fact, the selectivity behavior of the proposed NO2- ion-selective electrode shows great improvements compared to the previously reported electrodes for nitrite ion. The proposed electrodes could be used for at least 2 months without any significant changes in potentials. The electrode was successfully applied to the determination of nitrate ion concentrations in sausage and milk samples.     

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.     

Determination of SCN- in urine and saliva of smokers and non-smokers by SCN(-)-selective polymeric membrane containing a nickel(II)-azamacrocycle complex coated on a graphite electrode.

The construction, performance characteristics, and application of a novel polymeric membrane coated on a graphite electrode with unique selectivity towards SCN- are reported. The electrode was prepared by incorporating Ni(II)-2,2,4,9,9,11-hexamethyltetraazacyclotetradecanediene perchlorate into a plasticized poly(vinyl chloride) membrane. The influences of membrane composition, pH and foreign ions were investigated. The electrode displays a near Nernstian slope (-57.8 mV decade-1) over a wide concentration range of 1 x 10(-7)-1 x 10(-1) M of SCN- ion. The electrode has a detection limit of 4.8 x 10(-8) M (2.8 ng/cm3) SCN- and shows response times of about 15 s and 120 s for low to high and high to low concentration sequences, respectively. The proposed sensor shows high selectivity towards SCN- over several common organic and inorganic anions. The electrode revealed a great enhancement in selectivity coefficients and detection limit for SCN-, in comparison with the previously reported electrodes. It was successfully applied to the direct determination of SCN- in milk and biological samples, and as an indicator electrode in titration of Ag+ ions with thiocyanate.     

Moclobemide-selective membrane electrode and its pharmaceutical applications

A liquid membrane electrode prepared with moclobemide-dipicrylamine ion-pair complex, dissolved in nitrobenzene as solvent, was studied for analytical performance. The linear response covers the range 10(-3)-10(-6) M moclobemide solution, with a slope of 50.7 mV decade(-1) (pH range 3.5-8). The detection limit is 3 x 10(-7) M. The electrode shows stability, good reproducibility and fast response. The selectivity of the electrode is good. There are two important interfering ions: mianserin and thiamine (Vitamin B(1)). The compression excipients (such as Mg(2+), starch, talcum powder) do not interfere. These characteristics of the electrode enabled it to be used for the determination of moclobemide in drugs and as an active substance, via indirect and direct potentiometric methods. Via an indirect potentiometric method moclobemide, as an active substance, can be determined with an average recovery of 99.96% and a relative standard deviation of 0.85%, and this method can also be used for its determination in drugs with a relative standard deviation of < 2%. The electrode is useful for the determination of the dissolution rate of moclobemide tablets. The physical processes are numerically simulated by typical equations. The apparent first-order rate constants for disintegration and dissolution were calculated.     

Potentiometric determination of trace silver based on the use of a carbon paste electrode

A carbon paste electrode used as a sensor for silver has been developed and electrode response characteristics have been investigated. The electrode exhibits linear response to the logarithm of the concentration of silver from 5 x 10(-7)M to 1 x 10(-2)M, with a response slope of 63 +/- 2 mV. The detection limit according to IUPAC recommendations is 1 x 10(-7)M. This electrode has been used to determine trace silver in fixing solutions and waste electroplate solutions with good results.     

Modulating the redox properties of an osmium-containing metallopolymer through the supporting electrolyte and cross-linking

Thin films of the perchlorate salt of an [Os(N,N'-alkylated-2,2'-biimidazole3)2+/3+-containing polymer have been formed on planar platinum microelectrodes. The electrochemical response associated with the Os2+/3+ couple occurs at -0.19 V. In aqueous perchlorate media at near-neutral pH the voltammetric response is close to that expected for an electrochemically reversible reaction involving a surface-confined reactant. Chronoamperometry conducted on a microsecond time scale indicates that the film and solution resistances are comparable for low concentrations of supporting electrolyte. However, for LiClO4 concentrations greater than 0.4 M, RFilm contributes less than 25% of the overall cell resistance. These results suggest that when the film is dehydrated and the density of redox centers is increased, electron or hole hopping dominates the rate of homogeneous charge transport through the film. The rate of homogeneous charge transport, characterized by D(CT)1/2Ceff, where DCT is the homogeneous charge transport diffusion coefficient and Ceff is the effective concentration of osmium centers within the film, depends weakly on the concentration of LiClO4 as supporting electrolyte decreasing from (8.1 +/- 0.16) x 10(-9) to (4.7 +/- 0.4) x 10(-9) mol cm(-2) s(-1/2) as the perchlorate concentration increases from 0.1 to 1.0 M. These values are about 2 orders of magnitude lower than those of the chemically cross-linked chloride salt of the polymer. The rate of heterogeneous electron transfer is unusually rapid in this system and increases from (5.2 +/- 0.4) x 10(-3) to (7.8 +/- 0.4) x 10(-3) cm s(-1) on going from 0.1 to 0.4 M LiClO4 before becoming independent of the supporting electrolyte concentration at (9.2 +/- 0.6) x 10(-3) cm s(-1) for [LiClO4] > or = 0.6 M.     

Adsorptive stripping voltammetry for the determination of nifedipine in human serum

Adsorptive stripping voltammetry is used for the determination of trace levels of nifedipine. The conditions for preconcentration on the mercury drop electrode have been studied and the final measurements are made by differential pulse voltammetry. The response is linear from 2 x 10(-9) to 1 x 10(-7)M and can be extended to 10(-6)M by a change in conditions. The stripping peak has been used for determination of the drug in formulations, with a relative standard deviation of 0.8%. The method is applicable to the determination of nifedipine in blood-serum with a detection limit of 4.1 ng/ml.     

A metallic cobalt electrode for the indirect potentiometric determination of calcium and magnesium in natural waters using flow injection analysis

A flow injection analysis of Ca(2+) and Mg(2+) using indirect potentiometric detection in natural waters is proposed, where Ca(2+) or Mg(2+) are injected into a buffer carrier containing phosphate, resulting in the formation of Ca(3)(PO(4))(2) or Mg(3)(PO(4))(2). The consequent reduction in free phosphate in the carrier solution is detected using a metallic cobalt wire electrode. Indirect electrode response was used and the experimental conditions affecting electrode response were optimized. Responses were linear in the concentration range 5x10(-4) to 5x10(-3) M with a detection limit of 1x10(-5) M in 20 mM phosphate buffer at pH 8.0. The relative standard derivation at 1 mM of Ca(2+) and Mg(2+) were 3.9 and 3.7% (n=10), respectively. EGTA and 8-hydroxyquinoline were used as the masking agents for Ca(2+) and Mg(2+), respectively. Concentrations of Ca(2+) and Mg(2+) in natural waters were successfully determined by the proposed method.     

Coated-wire copper(II)-selective electrode based on phenylglyoxal-α-monoxime ionophore

A copper(II) ion-selective electrode based on a recently synthesized 2-quinolyl-2-phenylglyoxal-2-oxime (phenylglyoxal-alpha-monoxime) has been developed. The PVC-based membrane containing phenylglyoxal-alpha-monoxime, dibutyl phthalate as plasticizer, and sodium tetraphenylborate as anion excluder and membrane modifier, was directly coated on the surface of a platinum-wire electrode. The response of the electrode was linear with a near-Nernstian slope of 28.2 mV decade(-1) within the Cu2+ ion concentration range 1x10(-6)-1x10(-1) mol x L(-1). The response time for the proposed electrode to achieve a 95% steady potential for Cu2+ concentrations ranging from 1x10(-1) to 1x10(-6) mol x L(-1) is between 10 and 50 s, and the electrode is suitable for use within the pH range of 3 to 6.5. The electrode has a detection limit of 5x10(-7) mol x L(-1) Cu2+ and its selectivity relative to several alkali, alkaline earth, transition, and heavy metal ions was good. The coated-wire electrode could be used for at least two months without a considerable alteration of its potential. Applications of the electrode for determination of copper in milk powder samples and as an indicator electrode for potentiometric titration of Cu2+ ion using EDTA are reported.     

A mercury(II) ion-selective electrode based on N,N-dimethylformamide-salicylacylhydrazone as a neutral carrier.

A new PVC membrane mercury(II) ion electrode based on N,N-dimethylformamide-salicylacylhydrazone (DMFAS) as an ionophore is described, which shows excellent potentiometric response characteristics and displays a linear log[Hg(2+)] versus EMF response over a wide concentration range between 6.2 x 10(-7) and 8.0 x 10(-2) M with a Nerstian slope of 29.6 mV per decade and a detection limit of 5.0 x 10(-7) M. The response time for the electrode is less than 30 s and the electrode can be used for more than 2 months with less than a 2 mV observed divergence in a potentials. The proposed electrode exhibits very good selectivity for mercury(II) ions over many cations in a wide pH range (pH 1 - 4). The electrode was also applied to the determination of a mercury(II) ion in vegetables and in Azolla filiculoides.