Flow injection potentiometric stripping analysis and potentiometric stripping coulometry

Summary Potentiometric Stripping Analysis is used as a detection method for Flow Injection Analysis. A wall-jet glassy carbon disc electrode is applied for the determination of zinc, cadmium, and lead. Microliter samples are sufficient for high-speed determination in the ng-range. The sample throughout is up to 180 per hour depending on the metal ion concentration. The influence of various parameters on the stripping time is investigated.In addition the new concept of Potentiometric Stripping Coulometry is presented. Based on Faraday's law the measured stripping time can be used to calculate the mass of deposited metal. Provided that the deposition is complete the value found is identical to the mass totally present in the sample. Using lead as an example the accuracy of the determination is demonstrated for the wall-jet electrode. The application of a porous carbon felt electrode increases the speed of deposition. Optimum parameters are given for exhaustive depletion.

---

Fließinjektion zur potentiometrischen Stripping-Analyse und potentiometrischen Stripping-Coulometrie

Zusammenfassung Die potentiometrische Stripping-Analyse wird zur Detektion in der Fließinjektionsanalyse eingesetzt. Zur Bestimmung von Zink, Cadmium und Blei wird eine Wall-Jet Scheibenelektrode aus Glaskohlenstoff verwendet. Bei Injektion vonl-Mengen sind Schnellbestimmungen im ng-Bereich möglich. Je nach Metallionenkonzentration läßt sich ein Probendurchsatz von bis zu 180 pro Stunde erreichen. Der Einfluß verschiedener Parameter auf die Strippingzeit wird untersucht. Weiterhin wird das neue Konzept der potentiometrischen Stripping-Coulometrie vorgestellt. Die abgeschiedene Metallmasse kann aus der gemessenen Strippingzeit und dem zu berechnenden Oxydationsstrom ermittelt werden. Nach vollständiger Abscheidung ist diese Masse der gesamten in der Probe enthaltenen Masse gleich. Am Beispiel einer Bleibestimmung mit der Wall-Jet-Elektrode wird die Richtigkeit dieser Methode belegt. Durch die Verwendung einer Carbonfilzelektrode wird die Geschwindigkeit der vollständigen Abscheidung erhöht. Der Einfluß von Flußrate und injizierter Menge wird untersucht.

     

Relative stability of linear and cyclic configurations of systems containing four atoms of nitrogen,carbon, or oxygen

Conclusions The present article has been devoted to an investigation of the relative stability of various conceivable structures of systems X₄ (where X=C, CH, N, or O). We regard the comparative regularities which we have discovered as reliable, in spite of the use of MHM, in which no account is taken in any explicit way of the interelectronic interaction. We have considered homoatomic systems, where, on the qualitative side many conclusions are essentially of a theoretical-group character, while from a quantitative point of view the accuracy of the results obtained is increased because of the justifiable similarities assumed in the approximations of the matrix elements (both diagonal and nondiagonal). We have also investigated the geometry of the molecules, a problem of the solution of which the MHM method (as shown by comparing this with the SSP-MO [26] method) is remarkably effective.The main results of the present work are in our view to be found in the great similarity discovered in the structures of the systems C₄H₄ and N₄ (and their appreciable difference from the structure of the O₄ molecule). Therefore, returning to the over-all problem formulated at the beginning of this article, we are able to emphasize that the hypothesis of the possible formation of the N₄ system by combination of molecular nitrogen in certain complexes of the transition metals [1] is still further confirmed.N. S. Kurnakov Institute of General and Inorganic Chemistry of the Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 10, No. 4, July–August, 1969.     

Flow injection potentiometric determination of amitriptyline hydrochloride

New plastic membrane electrodes for amitriptyline hydrochloride (AmCl) based on amitriptylinium phosphotungstate (Am-PTA); amitriptylinium phosphomolybdate (Am-PMA) and a mixture of both (Am-PTA/PMA) were prepared. The electrodes were fully characterized in terms of their composition, life span, pH and temperature and then were applied to the potentiometric determination of the amitriptylinium ion in its pure state and pharmaceutical preparations and flow injection conditions. The selectivity of the electrodes towards many inorganic cations, sugars and amino acids was also tested.     

Flow injection potentiometric determination of clobutinol hydrochloride

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

Flow injection potentiometric determination of pipazethate hydrochloride

New plastic membrane electrodes for pipazethate hydrochloride based on pipazethatium phosphotungstate, pipazethatium phosphomolybdate and a mixture of the two were prepared. The electrodes were fully characterized in terms of composition, life span, pH and temperature and were then applied to the potentiometric determination of the pipazethate ion in its pure state and pharmaceutical preparations under batch and flow injection conditions. The selectivity of the electrodes towards many inorganic cations, sugars and amino acids was also tested.     

Two-photon laser-induced fluorescence in oxygen and nitrogen atoms

Two-photon absorption is used to populate the 3p ³P state of O and the 2s²2p²3p⁴D^o state of N in a flow discharge. Exciting photons are produced by anti-Stokes Raman frequency conversion of tunable UV laser radiation; the resulting near IR fluorescence from the excited state yielded lifetimes, quenching rates, and relative two-photon transition probabilities.     

Flow injection potentiometric sensor for determination of phenylpropanolamine hydrochloride

A new polymeric membrane electrode has been constructed for the determination of phenylpropanolamine hydrochloride. The electrode was prepared by solubilizing the phenylpropanolamine-phosphomolybdate ion associate into a polyvinyl chloride matrix plasticized by dibutylphthalate as a solvent mediator. The electrode showed near-Nernstian response over the concentration range of 1 × 10^?5–1 × 10^?2 M with low detection limit of 6.3 × 10^?6 M. The electrode displays a good selectivity for phenylpropanolamine with respect to a number of common inorganic and organic species. The electrode was successfully applied to the potentiometric determination of phenylpropanolamine ion in its pure state and its pharmaceutical preparation in batch and flow injection conditions.     

Studies on the cationic selectivity of the potentiometric membrane containing thiamine metatungstate as ionophore

An unconventional structure was obtained by extraction of K⁺ ions with nitrobenzene solution of thiamine metatungstate. This shows that K⁺ penetration into the organic phase is not an exchange process. The solution of thiamine metatungstate in nitrobenzene acts as a spacial structure that entraps K⁺ ions in a molar ratio of 1 : 2. The absence of a chemical reaction between K⁺ and the metatungstic anion (proved experimentally) and the specificity of the interaction with K⁺, suggests that the formation of the structure potassium – thiamine metatungstate (KTM) could be controlled by dimensional criteria. The nitrobenzene solution of KTM shows a remarkable potentiometric selectivity for K⁺ compared with any other alkaline and alkaline earth cations. The potentiometric K⁺-selective electrode, based on KTM as ionophore, responds linearly in the range 3.8 × 10^–5–1.0 × 10^–1 mol/L, with a slope of 56 mV/ decade and a detection limit of 1.2 × 10^–5 mol/L. The electrode maintained these response characteristics over a period of more than two months. Received: 12 May 1998 / Revised: 28 July 1998 / Accepted: 30 July 1998     

Studies on the cationic selectivity of the potentiometric membrane containing thiamine metatungstate as ionophore

An unconventional structure was obtained by extraction of K⁺ ions with nitrobenzene solution of thiamine metatungstate. This shows that K⁺ penetration into the organic phase is not an exchange process. The solution of thiamine metatungstate in nitrobenzene acts as a spacial structure that entraps K⁺ ions in a molar ratio of 1 : 2. The absence of a chemical reaction between K⁺ and the metatungstic anion (proved experimentally) and the specificity of the interaction with K⁺, suggests that the formation of the structure potassium – thiamine metatungstate (KTM) could be controlled by dimensional criteria. The nitrobenzene solution of KTM shows a remarkable potentiometric selectivity for K⁺ compared with any other alkaline and alkaline earth cations. The potentiometric K⁺-selective electrode, based on KTM as ionophore, responds linearly in the range 3.8 × 10^–5–1.0 × 10^–1 mol/L, with a slope of 56 mV/ decade and a detection limit of 1.2 × 10^–5 mol/L. The electrode maintained these response characteristics over a period of more than two months. Received: 12 May 1998 / Revised: 28 July 1998 / Accepted: 30 July 1998     

SINDO1 II. Application to ground states of molecules containing carbon,nitrogen and oxygen atoms

Molecular geometries, binding energies, ionization potentials and dipole moments are calculated by the SINDO1 method for a large number of molecules containing C, N and O atoms. Comparison is made with MINDO/3, MNDO and where possible with STO-3G results. The explicit data and an error statistics show the relative merits of SINDO1.     

Flow injection potentiometric determination of paraquat in formulations and biological samples

A flow injection potentiometric method for the rapid determination of paraquat in herbicide formulations and biological samples is described. It is based on the utilization of a flow-through potentiometric detector containing polyvinyl chloride-immobilised octamethylcyclotetrasiloxane, a lipophilic plasticizer (tetra-n-undecyl 3,3′,4,4′-benzophenone tetracarboxylate) and membrane additive potassium tetrakis(4-chlorophenyl)borate. The detector was minimally interfered by the presence of constituents such as Na⁺, K⁺, Ca²⁺, Mg²⁺, glucose, urea, lactic and citric acids at physiological levels, respectively. Good correlation between results of the proposed method and HPLC for the formulation samples was found, while results for the determination of paraquat in biological samples such as urine, vomitus and stomach washout was less satisfactory.     

Fluorinated azines and benzazines containing oxygen or sulfur atoms

In the frames of this review article the recently obtained data on synthetic approaches to fluorinated oxa(thia)azines and benzazines, their chemical properties, structure, and biological activity have been analyzed.     

Syntheses and reactivity of novel unsaturated cyclic compounds containing phosphorus atoms

Kinetic stabilization of compounds containing heavy main-group elements through the use of bulky substituents is of current interest. The widely used 2,4,6-tri-t-butylphenyl group (Mes*) is recognized as a powerful bulky protecting group and has enabled us to successfully prepare various types of phosphorus compounds with unusual structures. When a phosphaalkyne carrying Mes* was treated with tBuLi and then quenched with MeOH, a 1,3-diphosphacyclobutene was obtained, whereas, when MeI was used as a quencher, a 1,3-diphosphacyclobutane-2,4-diyl was formed almost quantitatively as a stable biradical compound. The reaction mechanism for the formation of both compounds can be explained by a phosphide intermediate, which can be formed via dimerization of the phosphaalkyne promoted by tBuLi. Some other diphosphacyclobutane-2,4-diyls with various substituents were prepared in a similar fashion and showed interesting reactivities including ring expansion, oxidation, isomerization and so on.     

Synthesis of pyrimidinophanes containing nitrogen atoms in polymethylene bridges

The reactions of 1,3-bis(-bromobutyl- or -pentyl)-6-methyluracil with 1,3-bis(-ethylaminobutyl- or -pentyl)-6-methyluracil afforded pyrimidinophanes containing N atoms in bridging polymethylene chains. Individual geometric isomers of pyrimidinophanes were isolated. The structure of one of these isomers was established by X-ray diffraction analysis. Quaternization of the bridging N atoms with o-nitrobenzyl bromide gave rise to water-soluble pyrimidinophanes.     

Flow injection analysis of fluoride in electroplating baths with potentiometric detection

A high dispersion FIA system with a fluoride selective and a double junction reference electrode in cascade arrangement was developed for the determination of the fluoride content in chromium electroplating baths. The analyses of seven synthetic baths prepared in the laboratory and two samples provided by the industry gave results with a mean recovery value of 100.5%, and a mean variation coefficient of 1.6%. These data were better than those obtained by the EDTA complexometric titration, the reference technique, with a mean recovery of 94.0% and a mean variation coefficient of 7.5%. The sampling rate for the FIA manifold was 20 samples per hour. Received: 27 November 1997 / Revised: 24 February 1998 / Accepted: 1 March 1998     

Flow injection analysis of fluoride in electroplating baths with potentiometric detection

A high dispersion FIA system with a fluoride selective and a double junction reference electrode in cascade arrangement was developed for the determination of the fluoride content in chromium electroplating baths. The analyses of seven synthetic baths prepared in the laboratory and two samples provided by the industry gave results with a mean recovery value of 100.5%, and a mean variation coefficient of 1.6%. These data were better than those obtained by the EDTA complexometric titration, the reference technique, with a mean recovery of 94.0% and a mean variation coefficient of 7.5%. The sampling rate for the FIA manifold was 20 samples per hour.     

Synthesis and potentiometric selectivity study of new spiro-14-crown-4 derivatives

Abstract

Four new compounds with 14-crown-4 attached to spirocyclopentane or spirocyclohexane were synthesized and tested for potentiometric selectivity for lithium ion in polyvinyl chloride membrane electrodes. Four plasticizers were studied and the addition of tri-octylphosphine oxide (TOPO) was investigated. One ionophore exhibited a sodium/lithium selectivity, K^pot _Li,Na by the matched potential method of 0.0028 in the presence of 1% TOPO, using o-nitro-phenylphenyl ether as plasticizer. Selectivities are reported for sodium, potassium, nickel, cobalt, barium and calcium.     

Kinetics of the reaction of alkyl bromides with nucleophiles containing nitrogen atoms

Kinetics of the reactions of propyl, propargyl and allyl bromides with anilines has been studied in methanol and dipolardmf. All reactions were found to be of second order. The values of the Bronsted slope (0–4) suggested that bond formation occurs to a considerable extent in the transition state. Electron-donating substituents increased the rate, while electron-withdrawing groups decreased the rate. The magnitudes of the negative values (≈1) indicate that the reaction rate depends on the availability of electron-density on the nitrogen atom, which implies bond formation, suggesting that all the reactions are SN² in nature, forming a loose transition state. Isokinetic temperature values calculated from the three methods for the reaction of allyl bromide-anilines suggested that the reaction series indmf is entropy controlled while in a methanol medium hydrogen bonding is responsible for the solute-solvent interactions.