Bis-dimethylaminobenzaldehyde Schiff-base cobalt(II) complex as a neutral carrier for a highly selective iodide electrode.

A new solvent polymeric membrane electrode based on N,N'-bis-(dimethylaminobenzaldehyde)-glycine cobalt(II) [Co(II)-BDMABG] as a neutral carrier is described, which displays a preferential potentiometric response to iodide ion and an anti-Hofmeister selectivity sequence in the following order: I- > ClO4- > Sal- > SCN- > NO2- > Br- > NO3- > Cl- > SO3(2-) > SO4(2-). The electrode exhibits a near-Nernstian potential linear range of 9.0 x 10(-7)-1.0 x 10(-1) M with a detection limit of 6.8 x 10(-7) M and a slope of -53.0 mV/decade in pH 2.0 of a phosphate buffer solution at 20 degrees C. The response mechanism is discussed in view of the A.C. impedance technique and the UV spectroscopy technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains with satisfactory results.     

长寿命高选择性液膜碘离子电极的研究

合成了PVC-双硫腙-Hg(Ⅱ)载体.以该载体物质制备了高选择性碘离子电极,其选择性次序为:I^-》ClO₄^->SCN^->NO₂^-》Sal^-～Br^->NO₃^->Cl^-.电极对碘离子的线性响应范围为1×10^-3～5×10^-7mol/L,检测下限为2×10^-7mol/L,斜率为(59±1)mV/decade(16℃).并研究了电极的响应机理,表明系碘离子与载体中金属汞原子直接作用.将该电极应用于食盐中碘的测定,取得了满意的结果.     

Salicylate ion-selective electrode based on new tetranuclear copper complexes of O-vannlin-methionine as neutral carriers.

A new salicylate-selective PVC membrane electrode based on a new Schiff base tetranuclear copper complex of O-vannlin-methionine (Cu(II)(4)-TVM) as a neutral carrier is described. This electrode displays a preferential potentiometric response to salicylate and an anti-Hofmeister selectivity sequence in the following order: Sal(-) > ClO(4)(-) > SCN(-) > I(-) > NO(2)(-) > NO(3)(-) > Br(-) > Cl(-) > SO(3)(2-) > SO(4)(2-) > H(2)PO(4)(-). The electrode exhibits near-Nernstian potential linear range of 1.5 x 10(-6)-1.0 x 10(-1) M with a detection limit of 8.0 x 10(-7) M and a slope of -56.3 mV/decade in pH 3.0-8.0 of phosphorate buffer solution at 20 degrees C. Thanks to the tetranuclear copper(II) in the carrier, the electrode has the advantages of simplicity, fast response, fair stability and reproducibility and low detection limit. The response mechanism to the electrodes is discussed by the a.c. impedance technique and the UV spectroscopy technique. The electrode can be applied to analyses of medicine and the results obtained are in fair agreement with the results given by a standard method.     

Anion selective polymeric membrane electrodes based on cyclopalladated amine complexes

The potentiometric anion selectivity of two polymer membrane based electrodes (I and II) formulated with two new cyclopalladated amine complexes as the active components are examined. The electrodes exhibit a non-Hofmeister selectivity pattern with a significantly enhanced response towards thiocyanate, iodide and nitrite. The graph potential versus log c is linear over the concentration range 10(-6)-6x10(-2) M thiocyanate with electrode I and 10(-6)-10(-3) M with electrode II; 10(-5)-10(-2) M iodide with electrode I and 10(-3)-6x10(-2) M with electrode II; and 10(-3)-6x10(-2) M nitrite with both electrodes. The influence of the plasticizer and pH are studied. The potentiometric selectivity coefficients for I, II and blank membrane electrodes are reported. The selective interaction between Pd(II) thiocyanate, iodide and nitrite is postulated to be the reason for its higher response.     

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.     

Mercury(II) ion-selective electrodes based on p-tert-butyl calix[4]crowns with imine units.

A PVC membrane incorporating p-tert-butyl calix[4]crown with imine units as an ionophore was prepared and used in an ion-selective electrode for the determination of mercury(II) ions. An electrode based on this ionophore showed a good potentiometric response for mercury(II) ions over a wide concentration range of 5.0 x 10(-5) - 1.0 x 10(-1) M with a near-Nernstian slope of 27.3 mV per decade. The detection limit of the electrode was 2.24 x 10(-5) M and the electrode worked well in the pH range of 1.3 - 4.0. The electrode showed a short response time of less than 20 s. The electrode also showed better selectivity for mercury(II) ions over many of the alkali (Na+, -1.69; K+, -1.54), alkaline-earth (Ca2+, -3.30; Ba2+, -3.32), and heavy metal ions (Co2+, -3.67; Ni2+, -3.43; Pb2+, -3.31; Fe3+, -1.82). Ag+ ion was found to be the strongest interfering ion. Also, sharp end points were obtained when the sensor was used as an indicator electrode for the potentiometric titration of mercury(II) ions with iodide and dichromate ions.     

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.     

Highly selective thiocyanate electrode based on bis-[N-(2-hydroxyethyl)salicylaldimino]copper(II) complex as a neutral carrier.

A novel selective thiocyanate electrode of a PVC membrane based on bis-[N-(2-hydroxyethyl)salicylaldimino]copper(II) [Cu(II)-BNSDM] as a neutral carrier is reported. The selectivity sequence of this electrode is as follows: SCN- > ClO4- > I- > Sal- > Br- > NO2- > Cl- > NO3- > H2PO4- > SO4(2-), which is an anti-Hofmeister selectivity sequence. The electrode exhibits a Nernstian potential linear range to thiocyanate from 1.0 x 10(-1) to 6.0 x 10(-6) mol/L with a detection limit of 2.0 x 10(-6) mol/L and a slope of (-59.0+/-0.2)mV/decade in pH 5.0 of a phosphate buffer solution at 25 degrees C. Electrochemical impedance spectroscopy (EIS) and UV spectroscopy techniques were performed to understand the response mechanism of the electrode. The electrode had the advantage of simplicity, high selectivity, fast response and low detection limit compared with the other electrode, which had been reported before. The electrode had been applied to wastewater analysis, and the obtained results were satisfactory.     

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.     

Tetrakis(4-N,N-dimethylaminobenzene)porphyrinato]manganese(III) acetate as a novel carrier for a selective iodide PVC membrane electrode.

[5,10,15,20-Tetrakis(4-N,N-dimethylaminobenzene)porphyrinato]Mn(III) acetate (MnTDPAc) was applied as an ionophore for an iodide-selective PVC membrane electrode. The influences of the membrane composition, pH of the test solution and foreign ions on the electrode performance were investigated. The sensor exhibited not only excellent selectivity to iodide ion compared to Cl- and lipophilic anions such as ClO4- and salicylate, but also a Nernstian response with a slope of -59.4 +/- 1.2 mV per decade for iodide ions over a wide concentration range from 1.0 x 10(-2) to 7.5 x 10(-6) M at 25 degrees C. The potentiometric response was independent of the pH of the solution in the pH range of 2 - 8. The electrode could be used for at least 2 months without any considerable divergence in the potential. Good selectivity for iodide ion, a very short response time, simple preparation and relatively long-term stability were the silent characteristics of this electrode. It was successfully used as an indicator electrode in the potentiometric titration of iodide ions, and also in the determination of iodide from seawater samples and drug formulations.     

Chemically modified carbon paste electrode for determination of copper(II) by potentiometric method

The utility of carbon paste electrode modified with DTPT (3,4-dihydro-4,4,6-trimethyl-2(1H)-pyrimidine thione) for the potentiometric determination of Cu(II) in aqueous medium is demonstrated. The electrode exhibits linear response to Cu(II) over a wide concentration range (9.77x10(-7)-7.6x10(-2)) with Nernstian slope of 30+/-2 mV per decade. It has a response time of about 45 s and can be used for a period of two months with good reproducibility. The detection limit of this electrode was 7.0x10(-7) M. The proposed electrode shows a very good selectivity for Cu(II) over a wide variety of metal ions. This chemically modified carbon paste electrode was successfully used for the determination of Cu(II) in electronics waste sample solution.     

Ion-selective electrodes for anionic surfactants using a cyclam derivative as ionophore

The cyclam derivative 1,4,8,11-tetra(n-octyl)-1,4,8,11-tetraazacyclotetradecane (L) has been used as carrier for the preparation of PVC-based membrane ion-selective electrodes for anionic surfactants. Different membranes were prepared using L as ionophore, tetra-n-octylammonium bromide (TOAB) as cationic additive and dibutyl phthalate (DBP) or o-nitrophenyl octyl ether (NPOE) as plasticizers. The final used electrode contained a membrane of the following composition: 56% DBP, 3.4% ionophore, 3.8% TOAB and 36.8% PVC. This electrode displays a Nernstian slope of -60.0+/-0.9 mV/decade in a 2.0 x 10(-3) to 7.9 x 10(-6) mol dm(-3) concentration range and a limit of detection of 4.0 x 10(-6) mol dm(-3). The electrode can be used for 144 days without showing significant changes in the value of slope or working range. The electrode shows a selective response to dodecyl sulfate (DS-) and a poor response to common inorganic cations and anions. The selective sequence found was DS->ClO4->HCO3->SCN->NO3- approximately CH3COO- approximately I->Cl->Br->IO3- approximately NO2- approximately SO3(2-)>HPO4(2-)>C2O4(2-)>SO4(2-), i.e. basically following the Hoffmeister series except for the hydrophilic anion bicarbonate. Most of the potentiometric coefficients determined are relatively low indicating that common anions would not interfere in the DS- determination. A complete study of the response of the electrode to a family of surfactant was also carried out. The electrode showed a clear anionic response to DS- and to Na-LAS and a much poorer response to other anionic surfactants and to non-ionic surfactants. Also the electrode shows certain non-linear cationic response in the presence of cationic and zwitterionic surfactants. The electrode was used for the determination of anionic surfactants in several mixtures, and the results obtained were compared to those found using a commercially available sensor.     

Potentiometric determination of silver(I) by selective membrane electrode based on derivative of porphyrin.

The performance of silver metal complexes with meso-tetraphenylporphyrin ([H2T(4-CH3)]PP) as ionophores for ion-selective electrodes was studied. The electrode exhibited linear response with Nernstian slope of 59.2 +/- 1.0 mV per decade within the concentration range of 1.0 x 10(-7)-1.0 x 10(-1) M silver ions. The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot, was 1.0 x 10(-7) M. The response time of the electrode was < 10 s over the entire concentration range. The silver-selective electrode exhibited good selectivity for Ag(I) with respect to alkali, alkaline earth and heavy metal ions. The electrodes could be used at least three months without a considerable divergence in their potential. The electrodes are suitable for use in aqueous solutions in a wide pH range of 3.0-9.0. They were used as indicator electrodes in titration of Ag(I) with sodium iodide solution and were successfully applied to direct determination of silver in real samples.     

Fabrication of a multilayer film electrode containing porphyrin and its application as a potentiometric sensor of iodide ion

A novel iodide ion-selective electrode has been produced based on a molecular deposition technique in which water-soluble porphyrin was alternatively deposited with water-soluble polypyrrole on a 2-aminoethanethiol modified silver electrode. The potentiometric response is independent of pH of the solution between pH 1 and 7, while it is dependent on the nature of the medium. The electrode has a linear dynamic range between 1.6x10(-6) and 0.1 M with a Nernstian slope of 59 mV/decade and a detection limit of 1.0x10(-6) M in acetate buffer (0.1 M, pH 4.6). The electrode has the advantages of low resistance, short conditioning time and fast response.     

Differential pulse anodic stripping voltammetry of lead (lI) benzoylacetonate in chloroform: Application to the analysis of free-lead gasoline and gas oil samples

The voltammetric characteristics of lead(II) benzoylacetonate in chloroform at the mercury electrode are investigated. The conditions for nearly reversible reduction of lead(II) were optimized. Anodic stripping voltammetry for the determination of trace-lead was developed using differential pulse technique to strip amalgamed lead from hanging mercury drop electrode. The experimental conditions, such as scanning rate of electrode potential and deposition time of lead were optimized. The calibration graph was linear over concentration range 5x10(-8)-10(-6) M of lead(II). The detection limit was 2.5x10(-9) and the relative standard deviation for the determination of 4x10(-7) M Pb(II) was 2%. Preceded by decomposition of organolead compounds with concentrated nitric acid, then ashing at 300 degrees C and a solvent extraction of Pb(II) benzoylacetonate in chloroform, the suitability of the proposed method for the determination of lead in free-lead gasoline and gas oil was demonstrated as a typical example of application.     

Organic-inorganic composite cation-exchanger: poly-o-toluidine Zr(IV) phosphate-based ion-selective membrane electrode for the potentiometric determination of mercury

A new heterogeneous precipitate of an organic-inorganic composite cation-exchanger poly-o-toluidine Zr(IV) phosphate was utilized for the preparation of a Hg(II) ion-sensitive membrane electrode for the determination of Hg(II) ions in real aqueous as well as in real samples. The electrode showed good potentiometric response characteristics, and displayed a linear log[Hg(2+)] versus EMF response over a wide concentration range of 1 x 10(-1) - 1 x 10(-6) M with a Nernstian slope of 30 mV per decade change in concentration with a detection limit of 1 x 10(-6). The membrane electrode showed a very fast response time of 5 s and could be operated well in the pH range 2 - 8. The selectivity coefficients were determined by the mixed-solution method, and revealed that the electrode was selective in the presence of interfering cations; however most of these did not show significant interference in the concentration range of 1 x 10(-1) - 1 x 10(-4) M. The lifetime of the membrane electrode was observed to be 120 days. The analytical utility of this electrode was established by employing it as an indicator electrode in the potentiometric titrations of Hg(2+) ions from a synthetic mixture as well as drain water.     

Pulse radiolysis studies of the reactions of CO3*- and NO2* with nitrosyl(II)myoglobin and nitrosyl(II)hemoglobin

The reactions of carbonate radical anion [CO3*-, systematic name: trioxidocarbonate*1-] with nitrosyl(II)hemoglobin (HbFe(II)NO) and nitrosyl(II)myoglobin (MbFe(II)NO) were studied by pulse radiolysis in N2O-saturated 0.25 M sodium bicarbonate solutions at pH 10.0 and room temperature. The reactions proceed in two steps: outer-sphere oxidation of the nitrosyliron(II) proteins to their corresponding nitrosyliron(III) forms and subsequent dissociation of NO*. The second-order rate constants measured for the first reaction steps were (4.3 +/- 0.2) x 10(8) and (1.5 +/- 0.3) x 10(8) M(-1) s(-1), for MbFe(II)NO and HbFe(II)NO, respectively. The reactions between nitrogen dioxide and MbFe(II)NO or HbFe(II)NO were studied by pulse radiolysis in N2O-saturated 0.1 M phosphate buffer pH 7.4 containing 5 mM nitrite. Also for the reactions of this oxidant with the nitrosyliron(II) forms of Mb and Hb a two-step reaction was observed: oxidation of the iron was followed by dissociation of NO*. The second-order rate constants measured for the first reaction steps were (2.9 +/- 0.3) x 10(7) and (1.8 +/- 0.3) x 10(7) M(-1) s(-1), for MbFe(II)NO and HbFe(II)NO, respectively. Both radicals appear to be able to oxidize the iron(II) centers of the proteins directly. Only for the reactions with HbFe(II)NO it cannot be excluded that, in a parallel reaction, CO3*- and NO2* first react with amino acid(s) of the globin, which then oxidize the nitrosyliron(II) center.     

A highly selective iodide electrode based on the bis(benzoin)-semiethylenediamine complex of mercury(II) as a carrier

A new PVC membrane electrode based on the bis(benzoin)-semiethylenediamine (BBSEA) complex of Hg(II) is described which exhibits excellent selectivity towards iodide, related to the unique interaction between the central Hg(II) and the iodide ion. The electrode has a linear response to iodide from 5 × 10^–7 to 5 × 10^–4 mol/L with a slope of 58 mV/dec.(20°C). The response characteristics were investigated in detail and the mechanism of the electrode was studied with AC impedance and quartz crystal microbalance (QCM) techniques. It can be used for iodide determinations in drug preparations.     

Mechanistic studies of nitric oxide reactions with water soluble iron(II), cobalt(II), and iron(III) porphyrin complexes in aqueous solutions: implications for biological activity.

The reactions of nitric oxide and carbon monoxide with water soluble iron and cobalt porphyrin complexes were investigated over the temperature range 298-318 K and the hydrostatic pressure range 0.1-250 MPa [porphyrin ligands: TPPS = tetra-meso-(4-sulfonatophenyl)porphinate and TMPS = tetra-meso-(sulfonatomesityl)porphinate]. Large and positive DeltaS(double dagger) and DeltaV(double dagger) values were observed for NO binding to and release from iron(III) complexes Fe(III)(TPPS) and Fe(III)(TMPS) consistent with a dissociative ligand exchange mechanism where the lability of coordinated water dominates the reactivity with NO. Small positive values for Delta and Delta for the fast reactions of NO with the iron(II) and cobalt(II) analogues (k(on) = 1.5 x 10(9) and 1.9 x 10(9) M(-1) s(-1) for Fe(II)(TPPS) and Co(II)(TPPS), respectively) indicate a mechanism dominated by diffusion processes in these cases. However, reaction of CO with the Fe(II) complexes (k(on) = 3.6 x 10(7) M(-1) s(-1) for Fe(II)(TPPS)) displays negative Delta and Delta values, consistent with a mechanism dominated by activation rather than diffusion terms. Measurements of NO dissociation rates from Fe(II)(TPPS)(NO) and Co(II)(TPPS)(NO) by trapping free NO gave k(off) values of 6.3 x 10(-4) s(-1) and 1.5 x 10(-4) s(-1). The respective M(II)(TPPS)(NO) formation constants calculated from k(on)/k(off) ratios were 2.4 x 10(12) and 1.3 x 10(13) M(-1), many orders of magnitude larger than that (1.1 x 10(3) M(-1)) for the reaction of Fe(III)(TPPS) with NO.     

Co2+-selective membrane electrode based on the Schiff Base NADS

A new PVC membrane electrode for cobalt(II) ions based on a recently synthesized Schiff base of 5-((4-nitrophenyl)azo)- N-(2',4'-dimethoxyphenyl)salicylaldimine is reported. The electrode exhibits a Nernstian response for Co(2+) ions over a wide concentration range (9.0 x 10(-7)-1.0 x 10(-2) M) with a slope of 29(+/-1). The limit of detection is 8.0 x 10(-7) M. The proposed sensor revealed good selectivities over a wide variety of other cations including hard and soft metals. This electrode could be used in a pH range of 3.5-6.0. It was used as an indicator electrode in potentiometric titrations of cobalt(II) ions and can be used in the direct determination of Co(2+) in aqueous solutions.