Facilitated ion transfer of protonated primary organic amines studied by square wave voltammetry and chronoamperometry.

The transfer of the protonated forms of heptylamine, octylamine, decylamine, procaine and procainamide facilitated by dibenzo-18-crown-6 from water to a solvent polymeric membrane has been investigated by using cyclic square wave voltammetry. The experimental voltammograms obtained are in good agreement with theoretical predictions. The values of the standard ion transfer potential, complexation constant and diffusion coefficient in water have been obtained from these experiments, and have been used to draw some conclusions about the lipophilicity of these species and the relative stability of the organic ammonium complexes with dibenzo-18-crown-6. The results have been compared with those provided by linear sweep voltammetry. Calibration graphs were obtained with both techniques. An interesting chronoamperometric method for the determination of the diffusion coefficient of the target ion in the membrane has been developed and applied to all these protonated amines.

Assay of acetylcholinesterase activity by potentiometric monitoring of acetylcholine.

An acetylcholine-selective electrode based on a plasticized polymeric membrane has been developed. The electrode exhibited good selectivity for acetylcholine (ACh) over choline and some common ions, low drift, and a fast response to ACh. The response was linear over an ACh concentration range of 1×10(-6) to 1×10(-3) M with a slope of 59.1±0.1 and a detection limit of 1.5×10(-7)±1.2×10(-8) M. The electrode was used to monitor enzymatic ACh hydrolysis catalyzed by acetylcholinesterase (AChE) at different substrate and enzyme concentrations. A kinetic data analysis permitted the determination of the Michaelis-Menten constant of the enzymatic hydrolysis and AChE activity in the range of 2×10(-5) to 3.8×10(-1)U ml(-1).

Benzodipyrrole derivates as new ionophores for anion-selective electrodes: improving potentiometric selectivity towards divalent anions.

Two open substituted benzodipyrroles were tested as hydrogen-bond-forming anion ionophores for the development of anion-selective electrodes. These compounds were incorporated in plasticized polymeric membranes with different plasticizers, using different membrane compositions to explore their response towards several anions. The electrodes constructed with membranes containing 2-nitrophenyl octyl ether and a 0.5 molar ratio ionic additive/ionophore showed pronounced anti-Hofmeister behaviour, providing a significantly enhanced response towards the divalent anions sulfate, sulfite, thiosulfate and oxalate. The selected electrodes were also evaluated in terms of detection limits and selectivity. (1)H NMR experiments were carried out in an attempt to explain some aspects of the behaviour observed.

Ion transfer through solvent polymeric membranes driven by an exponential current flux.

General analytical equations which govern ion transfer through liquid membranes with one and two polarized interfaces driven by an exponential current flux are derived. Expressions for the transient and stationary E-t, dt/dE-E and dI/dE-E curves are obtained, and the evolution from transient to steady behaviour has been analyzed in depth. We have also shown mathematically that the voltammetric and stationary chronopotentiometric I(N)-E curves are identical (with E being the applied potential for voltammetric techniques and the measured potential for chronopotentiometric techniques), and hence, their derivatives provide identical information.

Voltammetric behaviour and square-wave voltammetric determination of the potent antioxidant and anticarcinogenic agent ellagic acid in foodstuffs.

The voltammetric behaviour of ellagic acid (EA) is investigated by cyclic, differential pulse and square-wave voltammetry (CV, DPV and SWV, respectively). Based on the anodic oxidation peak at approximately 0.42V in acetic/acetate buffer (pH 5.5) a robust and a highly reliable square-wave voltammetric method is presented for the determination of EA. The oxidation peak current was linearly dependent on the concentration of EA in the range of 1.0×10(-7)-1.5×10(-6)mol/L (r=0.9997), with a detection limit of 1.0×10(-8)mol/L (S/N=3) and a quantification limit of 3.4×10(-8)mol/L (S/N=10), good reproducibility and a satisfactory level of selectivity towards others polyphenols. The proposed method was applied to the determination of free and total EA in fruits, nuts and juices with good analytical results being obtained.

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.

Ion transfer across a liquid membrane. General solution for the current-potential response of any voltammetric technique.

An explicit analytical equation applicable to the study of reversible ion transfer at systems with two liquid/liquid polarizable interfaces is presented. This expression is valid for any multipotential step technique, which are all very adequate for the determination of standard transfer potentials and transport parameters of ions. The expression of the I/E response for linear sweep voltammetry and cyclic voltammetry can also be deduced as a particular case of this equation. The general solution given here is formally similar to that obtained for the application of any multipotential step sequence to a system with a single polarizable interface, since the method followed here is based on the same premises.

[A clinical study of adult autoimmune hepatitis in Valencia, Spain]. / Estudio clínico de la hepatitis autoinmune del adulto en Valencia.

OBJECTIVE: the clinical phenotype of autoimmune hepatitis (AIH) varies among geographical areas. The aim of this study is to determine the salient features of AIH in adult patients from the province of Valencia, Spain. MATERIAL AND METHODS: eighty-one patients with AIH attended to in eight acute-care hospitals between 1994 and 2003. New patients diagnosed with AIH during year 2003 were evaluated prospectively. Data from patients currently attending follow-up visits and diagnosed before 2003 were collected retrospectively. RESULTS: a total of 94% of patients were females. Forty-three percent were asymptomatic, 27% had acute hepatitis, and 30% had chronic hepatitis. Type 1 AIH was diagnosed in 90% of cases. Type 2 AIH was more frequent in younger patients, and presented with an acute pattern. One third of patients had cirrhosis at onset. Patients with cirrhosis were older than 60 years more frequently. Immunosuppressants were given to 57 patients, with complete or partial remission in 87.7%. There were no significant differences in response to immunosuppression according to presentation pattern or AIH subtype. CONCLUSIONS: AIH in Valencia was predominantly diagnosed in asymptomatic women. Most cases were type 1, and in 25% of patients another autoimmune disease coexisted. At the time of diagnosis one third of patients had cirrhosis, particularly those over 60 years.

Differential pulse voltammetry and additive differential pulse voltammetry with solvent polymeric membrane ion sensors.

The ion transfer across the water-solvent polymeric membrane interface is investigated by using a new device based on a modification of a commercial ion-selective electrode body that permits the accommodation of a platinum counter electrode inside the inner filling solution compartment and, therefore, use of a four-electrode potentiostat with ohmic drop compensation. This device is used here to apply two different double potential pulse techniques--differential pulse voltammetry and additive differential pulse voltammetry--which are more advantageous than other voltammetric techniques, such as normal pulse voltammetry or cyclic voltammetry, for the determination of the characteristic electrochemical parameters of the system. This is due to the concurrence of two factors in these double potential pulse techniques, the peak-shaped response together with a considerable reduction of undesirable current contributions.

Flow-through bulk optode for the fluorimetric determination of perchlorate.

A flow-through fluorescence bulk optode for the flow-injection determination of perchlorate is described. As the active constituents the optode incorporates the lipophilized pH indicator fluorescein octadecyl ester and methyl tridodecyl ammonium chloride, dissolved in a plasticized poly (vinyl) chloride membrane entrapped in a cellulose support. The optode is applied in conjunction with the flow injection technique for perchlorate determination at pH 4.5 (acetic-acetate). The sensor is readily regenerated with the pH 10.4 (TRIS) carrier solution. The analytical characteristics of this optode with respect to perchlorate response time, dynamic measurement range, reproducibility and selectivity are discussed. The proposed FI method is applied to the determination of perchlorate in waters from different sources.

Determination of zinc (II) in pharmaceuticals based on a flow-through bulk optode.

A method based on flow injection (FI), was applied for the determination of Zn (II) using a flow-through bulk optode membrane that incorporates 1-(2-pyridylazo)-2-naphthol in a plasticized poly (vinyl chloride) membrane entrapped in a cellulose support. The calibration graph plotting the reflectance at 562 nm versus [Zn (II)] was linear in the range 0.16-3.27 mgl(-1) (2.5 x 10(-6)-5 x 10(-5) M) with a detection limit of 0.10 mgl(-1). The variation coefficients of the sensor response for 0.33 mgl(-1) of Zn (II) were +/-0.11% for consecutive measurements (n=10), +/-0.19% between days (n=5) and +/-0.22% between different membranes (n=6). The sensor can be readily regenerated with the same acetic/acetate carrier of pH 3.9. The FI method proposed was applied to the determination of zinc (II) in pharmaceuticals.

Kinetic methods for the determination of cadmium(II) based on a flow-through bulk optode.

Three kinetic methods based on flow injection, flow, and stopped-flow injection were applied for the determination of Cd(II) using a flow-through bulk optode membrane that incorporates 1-(2-pyridylazo)-2-naphtol (PAN) in a plasticized poly(vinyl) chloride membrane entrapped in a cellulose support. The calibration graphs plotting the reflectance at 560 nm versus [Cd(II)](1/2) for the first two methods and versus [Cd(II)] for the third were linear up to 56.2 mg l(-1). The detection limits of the methods were 0.01, 0.06 and 0.8 mg l(-1), respectively. The FI method was selected for application purposes. The variation coefficient of the sensor response for 11.2 mg l(-1) of Cd(II) was +/-0.31 and +/-0.65% between different membranes. The sensor can be readily regenerated with a carrier (acetic-acetate) buffer of pH 4. The FI method was applied to the determination of cadmium in an alloy and in water.

Development of a new flow-through bulk optode for the determination of manganese(III).

A flow-through bulk optode based on the use of 1-(2-pyridylazo)-2-naphthol (PAN) immobilized in a plasticized poly(vinyl chloride) membrane entrapped in a cellulose support, in conjuntion with the flow injection analysis technique, is proposed for the determination of manganese(II). The calibration graph obtained at 570 nm was linear in the range 0.27-27.5 mg L(-1) (5 x 10(-6)-5 x 10(-4) M) Mn(II) with a detection limit of 0.18 mg L(-1). The coefficients of variation of the sensor response for 5.5 mg L(-1) of Mn(II) were +/-0.22% for consecutive measurements (n = 10), +/-0.48% between days (n = 5) and +/-0.38% between different membranes (n = 6). The sensor was readily regenerated with the carrier acetic acid/acetate buffer of pH 4.5. The method was applied to the determination of manganese in steels, waters and lemon tree leaves.

Flow injection potentiometry of primary and interfering ion with a gold complex ion-exchange membrane.

A gold(I) organic complex in the perchlorate form was incorporated in plasticized poly(vinyl chloride) (PVC) membranes and the potentiometric response towards perchlorate (primary ion) and permanganate (interfering ion) was studied. Membranes with 2:1 and 1:2 (w/w) plasticizer to PVC ratio were selected for the determination of primary and interfering ions, respectively. In the selected flow injection conditions, a linear relationship between peak height and log c were obtained between 1x10(-2) and 2x10(-5) mol l(-1) perchlorate and 1x10(-3)-1x10(-5) mol l(-1) permanganate. Good reproducibilities and excellent selectivity coefficients towards many common ions were obtained. The methods proposed were applied satisfactorily to the determination of perchlorate in water and of permanganate in pharmaceutical preparations. Permanganate can be directly determined even in the presence of a high amount of manganese dioxide.

A new procedure for the construction of flow-through optodes. Application to determination of copper (II).

A new procedure for constructing an optical fibre reflectance, bulk optode membrane type, sensor is presented. The optode membrane consists of a plasticized poly (vinyl chloride) membrane in which the ionophore is dissolved, entrapped in a cellulose support. The new optode with the dye indicator 1-(2-pyridylazo)-2-naphthol (PAN) was incorporated in a new flow-through cell and the injection system was optimized to determine Cu (II) at 567 nm in the range 5 x 10(-5)-10(-3) M. The response was reproducible and the optode can be regenerated using 10(-2) M EDTA followed by water. The method was applied to the determination of copper in real samples.

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.

[Do patients with duodenal ulcer transmit Helicobacter pylori to their relatives?]. / Los pacientes con úlcera duodenal transmiten el Helicobacter pylori a sus familiares?

The prevalence of IgG antibodies to Helicobacter pylori was determined with an enzyme-linked immunosorbent assay in 80 families who lived together with 40 duodenal ulcer patients in whom Helicobacter pylori had been cultured from a gastric biopsy (34 spouses, 31 children, 10 parents, 4 sisters and 1 brother) and in 112 controls from the same habitat and with similar age. The antibodies were positive in 38.4% of the relatives and in 36.6% of the controls, the difference was not significant. Among spouses of patients, 38.4% of those aged 25-39 years and 66.6% of those aged 40-67 years were positive, whereas controls showed a 29.2% and a 58.3% of positives respectively. The differences between both groups were not significant. Among children, 17.2% were positive and in parents 50%, whereas among controls with a similar age 26.3% and 62.5% respectively were positive. The differences between relatives and controls were not significant. We conclude that in our environment among consanguineous families living together and between spouses, person-to-person spread of Helicobacter pylori does not usually occur or it happens uncommonly.

Transient signals with an Antimony(V) ion-selective electrode: The relative signal return rate as a selectivity parameter.

The dynamic response of a Sb(5+) ion-selective electrode based on 1,2,4,6-tetraphenylpyridinium hexachloroantimonate(V) to different ions, ClO(-)(4), HgCl3(-)(3), AuCl(-)(4),TlCl(-)(4), SbCl(-)(6) and tetraphenylborate, in a flow-injection analysis system using a flow-through cell, is studied. The transient signals obtained are different for every ion. A parameter called relative return rate, defined as the ratio of the return rate to peak height, was found to be characteristic for each ion. It was constant up to a concentration range of three decades for those ions with selectivity coefficients K(pot)(sb,j) 1, thus providing a new source of analytical selectivity. Flow injection variables were studied in order to ascertain their influence on this new parameter.