Joaquín A. Ortuño

Differential pulse voltammetry for ion transfer at liquid membranes with two polarized interfaces.

A simple analytical expression for the response of the double-pulse technique differential pulse voltammetry (DPV) corresponding to ion transfer processes in systems with two liquid/liquid polarizable interfaces has been deduced. This expression predicts lower and wider curves than those obtained with a membrane system with a single polarizable interface. Moreover, the peak potential of these systems is shifted 13 mV from the half-wave membrane potential. We have applied this expression to study the ion transfer of drugs with different pharmacological activities (verapamil, clomipramine, tacrine, and imipramine), at a solvent polymeric membrane ion sensor.

Coated-wire ion-selective electrode for the determination of thallium(III)

The construction, performance characteristics and applications of a coated-wire thallium(III) ion-selective electrode, based on the ion pair between TlCl4- and the 1,2,4,6-tetraphenylpyridinium cation in a poly(vinyl chloride) matrix, are described. The influence of membrane composition, hydrochloric acid concentration and foreign ions was investigated. The electrode shows a near-Nernstian response over the thallium(III) concentration range 10–5–10–2M, with good selectivity and precision. Applications to the potentiometric titration of 0.25–5.0 mg of thallium(III) and to the direct potentiometric determination of thallium in sphalerites and zinc concentrates are reported.

Coated-wire ion-selective electrode for the determination of gold(III)

Abstract A coated-wire gold(III)-selective electrode based on the 1,2,4,6-tetraphenyl-pyridinium tetrachloroaurate(III) ion-pair is described. The response is Nernstian in the gold concentration range 10−2–3 × 10−6 (slope 59.0 mV/pAu). Of the 22 ions tested, only the interference of thallium(III) is important. The electrode is applied to the determination of gold in an Ag-Pd-Au alloy with satisfactory results.

Studies of ion transfer across liquid membranes by electrochemical techniques

The fundamentals and recent advances in ion transfer across the interface between two immiscible electrolyte solutions (ITIES) are reviewed. The different strategies developed to overcome the limitations of the traditional experimental studies with ITIES and to broaden its scope of applications are discussed. Special attention is given to studies of ion transfer through liquid membranes which contain two ITIES, one or both of which can be polarized. Theoretical and experimental studies on the application of different galvanostatic and potentiostatic electrochemical techniques to the study of such systems are described, emphasizing their unique characteristics. The article also includes sections devoted to facilitated ion transfer, liquid/liquid micro-interfaces and the use of weakly supported media.

Physical insights of salt transfer through solvent polymeric membranes by means of electrochemical methods.

A combined voltammetric study of the joint transfer of the two constituting ions of a water-soluble salt has been carried out using normal-pulse voltammetry, linear-sweep voltammetry and square-wave voltammetry in a system with two liquid-liquid polarized interfaces. As a result, we have explained the voltammetric features that allow us to distinguish this uptake from that corresponding to two equally charged ions, in spite of the appearance in both situations of two current peaks with the same sign in both square-wave and linear-sweep voltammograms, and we have found that linear-sweep voltammetry and square-wave voltammetry complement each other excellently.A theoretical comparison with a system of a single polarized interface has also been made, showing that these systems are much less appropriate for characterizing these salt-ion transfers.

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.

Determination of chlorine and dissolved oxygen in waters and of ascorbic acid in pharmaceuticals by iodimetric potentiometric titration using a plasticized poly(vinyl chloride) membrane electrode

Abstract The response to triiodide of an electrode based on a membrane containing poly(vinyl chloride) and 2-nitrophenyl octyl ether as plasticizer in a 1:2 ( w w ) ratio is studied. The electrode is suitable for the automatic potentiometric titration of triiodide in the concentration range 10 −5 –10 −3 mol l −1 with thiosulphate. The electrode has been satisfactorily applied to the determination of chlorine and dissolved oxygen in tap waters and that of ascorbic acid in pharmaceuticals. Possible explanations for the response of the membrane to triiodide are included.

Rubber-based substrates modified with carbon nanotubes inks to build flexible electrochemical sensors

The development of a solid-contact potentiometric sensor based on conducting rubbers using a carbon nanotubes ink is described here. Commercial rubbers are turned into conductive ones by a simple and versatile method, i.e. painting an aqueous dispersion of single-walled carbon nanotubes on the polymer surface. On this substrate, both the working ion-selective electrode and the reference electrode are built in order to form an integrated potentiometric cell. As a proof-of-principle, selective potassium electrodes are fully characterized giving comparable performances to conventional electrodes (sensitivity, selectivity, stability, linear range, limit of detection and reproducibility). As an application of the rubber-based electrodes, a bracelet was constructed to measure potassium levels in artificial sweat. Since rubbers are ubiquitous in our quotidian life, this approach offers great promise for the generation of chemical information through daily objects.

New approach for the potentiometric-enzymatic assay of reversible-competitive enzyme inhibitors. Application to acetylcholinesterase inhibitor galantamine and its determination in pharmaceuticals and human urine

A new kinetic-potentiometric method for the characterization and analytical determination of competitive reversible enzyme inhibitors was developed. The method is based on a mathematical approach, assuming that the reaction proceeds at the steady state, which permits calculation of a tentative substrate concentration to be used to determine low inhibitor concentrations and to obtain the value of inhibition constant corresponding to the inhibitor. The mathematical approach predicts a linear relationship between the inverse of the relative inhibition and the inverse of the inhibitor concentration. The method developed is applied to the acetylcholinesterase inhibitor galantamine, using an acetylcholine-selective electrode. A linear relationship for galantamine concentration from 2×10(-8) to 1×10(-6)M and a limit of detection of 5.4×10(-9)M was found. A value for KI(Gal) of 2.0×10(-7)±0.1×10(-7)M was obtained. The effect of several other drugs and of the main galantamine metabolite excreted in urine was studied. The method was satisfactorily applied to the determination of galantamine in pharmaceuticals and human urine.

Flow-injection potentiometric determination of triiodide by plasticized poly(vinyl chloride) membrane electrodes and its application to the determination of chlorine-containing disinfectants.

Plasticized poly(vinyl chloride) (PVC) membranes of different compositions were tested for use in the construction of potentiometric flow detectors for triiodide. A membrane with a 2:1 (w/w) 2-nitrophenyl octyl ether to PVC ratio was selected. The influence of thiosulphate in the carrier solution composition and of the flow-injection variables on the determination of triiodide was studied. In the selected conditions, a linear relationship between peak height and log[I(3)(-)] was obtained between 5 x 10(-6) and 1 x 10(-4)moll(-1) triiodide. Peak height relative standard deviations for 2 x 10(-5) and 1 x 10(-4)moll(-1) triiodide were +/-0.4 and +/-1.8%, respectively, and sampling frequency was 80 samples per hour. The method proposed was applied satisfactorily to the iodometric determination of different chlorine-containing disinfectants, among them trichloroisocyanuric acid and dichloroisocyanurate in several types of commercial sample.