Potentiometric Electronic Tongue for Quantitative Ion Analysis in Natural Mineral Waters.

The present paper addresses the development and use of a new potentiometric electronic tongue for both qualitative and quantitative characterization of natural mineral waters. The electronic tongue is particularly related to the conductivity and ion content of/in the water sample. The analytical system is based on six ion-selective electrodes whose membranes are formulated to provide either cationic or anionic response and considering plasticizers with different dielectric constants (bis(2-ethylhexyl) sebacate, 2-nitrophenyl octyl ether or tricresylphosphate), while keeping the polymeric matrix, i.e., poly(vinyl chloride). Notably, the absence of any ionophore in the membrane provides a general response profile, i.e., no selectivity toward any special ion, which is convenient for the realization of an effective electronic tongue. The dynamic response of the tongue toward water samples of different chemical compositions and geographical locations has been obtained. At the optimized experimental conditions, the tongue presents acceptable repeatability and reproducibility (absence of hysteresis). The principal component analysis of the final potential values observed with the six electrodes allows for the differentiation and classification of the samples according to their conductivity, which is somehow related to the mineralization. Moreover, quantitative determination of the six main ions in the water samples (i.e., chloride, nitrate, hydrogen carbonate, sulfate, sodium, calcium, and magnesium) is possible by means of a simple linear calibration (and cross-validation) model.

Considerations about the Continuous Assay Methods, Spectrophotometric and Spectrofluorometric, of the Monophenolase Activity of Tyrosinase.

With the purpose to obtain the more useful tyrosinase assay for the monophenolase activity of tyrosinase between the spectrofluorometric and spectrophotometric continuous assays, simulated assays were made by means of numerical integration of the equations that characterize the mechanism of monophenolase activity. These assays showed that the rate of disappearance of monophenol (VssM,M) is equal to the rate of accumulation of dopachrome (VssM,DC) or to the rate of accumulation of its oxidized adduct, originated by the nucleophilic attack on o-quinone by a nucleophile such as 3-methyl-2-benzothiazolinone (MBTH), (VssM, A-ox), despite the existence of coupled reactions. It is shown that the spectrophotometric methods that use MBTH are more useful, as they do not have the restrictions of the L-tyrosine disappearance measurement method, of working at pH = 8 and not having a linear response from 100 µM of L-tyrosine. It is possible to obtain low LODM (limit of detection of the monophenolase activity) values with spectrophotometric methods. The spectrofluorimetric methods had a lower LODM than spectrophotometric methods. In the case of 4-hydroxyphenil-propionic acid, the LODM obtained by us was 0.25 U/mL. Considering the relative sensitivities of 4-hydroxyanisole, compared with 4-hydroxyphenil-propionic acid, LODM values like those obtained by fluorescent methods would be expected.

Inexpensive ion-selective electrodes for the simultaneous monitoring of potassium and nitrate concentrations in nutrient solutions.

A fast, simple and inexpensive potentiometric method has been developed for the determination of the major ions potassium and nitrate in nutrient solutions, by means of ion-selective electrodes (ISEs) based on plasticized polyvinyl membranes containing an ion-exchanger. Tridodecylmethylammonium chloride (TDMACl) and potassium tetrakis(4-chlorophenyl)borate (KTClPB) were used as ion-exchangers for the nitrate and potassium electrodes, respectively. Electrode membranes built with different plasticizers, bis-[2-ethylhexyl]-sebacate (DOS), tricresyl phosphate (TCP) and 2-nitrophenyloctyl ether (NPOE), were tested, and NPOE was selected. The electrodes were calibrated over both wide and narrow concentration ranges and residual analysis was made. Based on the results of these calibrations, the method of standard addition was developed and found to be suitable for the simultaneous determination of potassium and nitrate in nutrient solutions. A large group of samples taken from different stages of hydroponic crops was analysed. Several approaches recommended for statistical comparisons of the results obtained by potentiometric and by reference methods were tested, obtaining satisfactory results. The potentiometric methodology developed is promising for monitoring the concentration of these essential nutrients in nutrient solutions.

In vivo measurement of pH and CO2 levels in the uterus of sows through the estrous cycle and after insemination.

The pH-CO2-HCO3- system is a ubiquitous biological regulator with important functional implications for reproduction. Knowledge of the physiological values of its components is relevant for reproductive biology and the optimization of Assisted Reproductive Technologies (ARTs). However, in situ measurements of these parameters in the uterus are scarce or null. This study describes a non-invasive method for in situ time-lapse recording of pH and CO2 within the uterus of non-anesthetized sows. Animals were at three different reproductive conditions, estrous with no insemination and two hours after insemination, and diestrous. From pH and CO2 data, HCO3- concentration was estimated. The non-invasive approach to the porcine uterus with novel optical probes allowed the obtaining of in situ physiological values of pH, CO2, and HCO3-. Variable oscillatory patterns of pH, CO2 and HCO3- were found independently of the estrous condition. Insemination did not immediately change the levels of uterine pH, CO2 (%) and HCO3- concentration, but all the values were affected by the estrous cycle decreasing significantly at diestrous condition. This study contributes to a better understanding of the in vivo regulation of the pH-CO2-HCO3- system in the uterus and may help to optimize the protocols of sperm treatment for in vitro fertilization.

A sustainable amperometric biosensor for the analysis of ascorbic, benzoic, gallic and kojic acids through catechol detection. Innovation and signal processing.

In this work, we present a new catechol amperometric biosensor fabricated on the basis of naturally available enzymes in common mushrooms. The biosensor response mechanism comprises the reduction of the quinone exclusively produced in the oxidation of the catechol present in the sample, which is catalyzed by tyrosinase enzyme. The new catechol biosensor has demonstrated excellent analytical performance at increasing catechol concentrations in the sample solution, which includes superior reproducibility for several electrodes and long-term stability. On top of that, the biosensing element used in the fabrication is a sustainable material, of low-cost and presents an excellent lifetime of years. Whether the catechol biosensor is operating in the presence of a compound influencing the reactions underlying the amperometric response (such as ascorbic, benzoic, gallic and kojic acids), this serves as an analytical platform to detect these compounds in real samples. Particularly, we introduce herein for the first time different treatments to process the current signal of the biosensor pursuing the linearity needed for the analytical application in real samples. In this sense, the catechol biosensor has been successfully applied to the detection of benzoic, gallic and kojic acids in juices, teas and cosmetic products, respectively.

Comparative enzymatic studies using ion-selective electrodes. The case of cholinesterases.

The application of traditional ion-selective electrodes for comparative enzymatic analysis was demonstrated for the first time in this study. A kinetic-potentiometric method based on the monitoring of the concentration of the ionic substrate involved in the enzymatic reaction catalyzed by different cholinesterases is used for this purpose. A comparative study was performed comprising both enzymatic assays using different ionic substrates and the corresponding inhibited reactions in presence of neostigmine (a synthetic anticholinesterase). The developed approach is used to obtain valuable comparative results through calculation of kinetic parameters, such as Michaelis and inhibition constants. Interesting results were obtained for acetylcholinesterase and butyrylcholinesterase enzymes, which were selected as proof-of-concept: (i) the binding affinity that these enzymes have for their natural substrates showed to be higher (acetylcholine and butyrylcholine respectively) than for their corresponding thiol derivatives (acetylthiocholine and butyrylthiocholine), which are traditionally used in spectrophotometric enzymatic assays; (ii) as expected, the maximum hydrolysis rate found in the assays of each enzyme was independent of the substrate used; (iii) acetylcholinesterase enzyme inhibition due to neostigmine was found to be higher (higher inhibition constant). Advantageously, the use of ion-selective electrodes permits to perform cholinesterases' enzymatic assays using their natural substrates and under physiological conditions, unlike the traditional spectrophotometric methods used in routine enzymatic assays. Importantly, while well-known enzymes are use throughout this work, this approach can be extended to other types of enzymatic assays as a tangible alternative to traditional spectrophotometric methods.

Theoretical Treatment of Ion Transfers in Two Polarizable Interface Systems When the Analyte Has Access to Both Interfaces.

A new theory is presented to tackle the study of transfer processes of hydrophilic ions in two polarizable interface systems when the analyte is initially present in both aqueous phases. The treatment is applied to macrointerfaces (linear diffusion) and microholes (highly convergent diffusion), obtaining analytical equations for the current response in any voltammetric technique. The novel equations predict two signals in the current-potential curves that are symmetric when the compositions of the aqueous phases are identical while asymmetries appear otherwise. The theoretical results show good agreement with the experimental behavior of the "double transfer voltammograms" reported by Dryfe et al. in cyclic voltammetry (CV) ( Anal. Chem. 2014 , 86 , 435 - 442 ) as well as with cyclic square wave voltammetry (cSWV) experiments performed in the current work. The theoretical treatment is also extended to the situation where the target ion is lipophilic and initially present in the organic phase. The theory predicts an opposite effect of the lipophilicity of the ion on the shape of the voltammograms, which is validated experimentally via both CV and cSWV. For the above two cases, simple and manageable expressions and diagnosis criteria are derived for the qualitative and quantitative study of ion lipophilicity. The ion-transfer potentials can be easily quantified from the separation between the two signals making use of explicit analytical equations.

Characterization of inclusion complexes of organic ions with hydrophilic hosts by ion transfer voltammetry with solvent polymeric membranes.

The quantitative characterization of inclusion complexes formed in aqueous phase between organic ions and hydrophilic hosts by ion-transfer voltammetry with solvent polymeric membrane ion sensors is studied, both in a theoretical and experimental way. Simple analytical solutions are presented for the determination of the binding constant of the complex from the variation with the host concentration of the electrochemical signal. These solutions are valid for any voltammetric technique and for solvent polymeric membrane ion sensors comprising one polarisable interface (1PI) and also, for the first time, two polarisable interfaces (2PIs). Suitable experimental conditions and data analysis procedures are discussed and applied to the study of the interactions of a common ionic liquid cation (1-octyl-3-metyl-imidazolium) and an ionisable drug (clomipramine) with two hydrophilic cyclodextrins: α-cyclodextrin and 2-hydroxypropyl-ß-cyclodextrin. The experimental study is performed via square wave voltammetry with 2PIs and 1PI solvent polymeric membranes and in both cases the electrochemical experiments enable the detection of inclusion complexes and the determination of the corresponding binding constant.

Binding studies and anion-selective electrodes with neutral isophthalamide-based receptors.

Two acyclic isophthalamide-based hosts have been synthesised and their anion binding properties have been evaluated by (1)H-NMR titrations. Different binding modes have been detected for the series of tested anions. The attachment of aminomethylpyrrole groups resulted in an improved binding selectivity. Additionally, the receptors have been incorporated as ionophores in plasticised polymeric membrane-based anion-selective electrodes. The potentiometric studies were in agreement with the NMR experiments and revealed a good sensing ability, considering the structural simplicity of the receptors and their interactions purely based on hydrogen bonding. These preliminary experiments have revealed an interesting selectivity towards highly hydrophilic anions such as fluoride and sulfate. Moreover, a particularly low detection limit (9 × 10(-7) M) has been determined for the fluoride anion.

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 carbazolo[1,2-a]carbazole derivative as ionophore for anion-selective electrodes: remarkable recognition towards dicarboxylate anions.

A new carbazolo[1,2-a]carbazole derivative was synthesized by expanding the binding cavity to explore the possibility of hosting larger anions such as dicarboxylate anions. The compound was incorporated as an ionophore into a membrane for an anion-selective electrode. The response of the electrode was evaluated for oxalate, malonate, succinate, glutarate and adipate in terms of calibration characteristics (slope, limit of detection and linear range of the response), response time, repeatability, reproducibility and selectivity. Nernstian reproducible responses, with very good detection limits, fast responses and selectivity not previously observed, were found for all the dicarboxylates anions, and the results were especially good in the case of glutarate. In order to obtain additional structural information about the complex formed between the ionophore and the dicarboxylate anions, (1)H NMR and fluorescence studies were carried out. The observed potentiometric selectivity depends on the good correspondence between the size of the carbazolocarbazole cavity and the length of the dicarboxylate anion, as supported by the NMR and fluorescence studies.

A SO2-selective electrode based on a Zn-porphyrin for wine analysis.

This work describes the assessment of a SO2-selective electrode based on the use of the neutral carrier 5,10,15,20-tetraphenyl(porphyrinate)zinc(II) in a PVC membrane plasticized with 2-nitrophenyl phenyl ether. After being conditioned in 2 mol L(-1) diethylamine solution for 24 h, the electrode exhibited selective anionic response toward the analyte in a concentration interval of more than four decades, with an slope of -59.5 mV dec(-1), a practical detection limit of 3.7×10(-6) mol L(-1) and a low limit of linear range of 7.2×10(-6) mol L(-1). The response mechanism is based on the displacement of the diethylamine:metalloporphyrin complex equilibrium within membrane bulk, inducing a variation in the cationic-sites to ionophore ratio. In turn, free hydroxyl ions are complexed by the displaced ionophore in a ratio 1:1 and translated as single negative charge nernstian response. Finally, the selectivity of the electrode is evaluated in view of its application to wine analysis. Results had high accuracy and precision when compared with a reference method.

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.

Kinetic effects of the complexation reaction in the facilitated ion transfer at liquid membrane systems of one and two polarized interfaces. Theoretical insights.

An in-depth study of the ion transfer facilitated by complexation in the organic phase (TOC mechanism) in liquid membrane systems of one and two polarized interfaces is carried out by taking into account the kinetic effects associated with the complexation reaction. Explicit analytical equations for the normal pulse voltammetric (I/E) and chronoamperometric (I/t) responses with an explicit dependence on the kinetic parameters of the chemical complexation are presented for both kinds of membrane system, which could be useful for modeling artificial and biological membranes. The equations are compared with those obtained by using the widely used approximation of total equilibrium conditions that leads to the transfer by interfacial complexation mechanism (TIC), which only depends on thermodynamic parameters. Simple methods are proposed that allow quantitative determination of the equilibrium and kinetic constants of the complexation reaction in the organic phase for both kinds of membrane system.

Use of a new ziprasidone-selective electrode in mixed solvents and its application in the analysis of pharmaceuticals and biological fluids.

The construction and characterization of a new ion-selective electrode for the determination of the antipsychotic ziprasidone in mixed solvents is presented. The electrode contains a plasticized polymeric membrane based on a ziprasidone-tetraphenylborate ion-exchanger. The influence of membrane composition on the electrode response towards ziprasidone in hydroalcoholic solutions was studied. The electrode displayed a stable response in a 2:3 (v/v) methanol/water medium from a ziprasidone concentration of 3 × 10(-6) M with a fast response time of less than 20 s. The electrode also showed good selectivity towards ziprasidone over common inorganic and organic compounds and several species with pharmacological activity. The electrode was successfully applied to the determination of ziprasidone in pharmaceuticals and human urine and serum.

A retrospective study on outcome of microscopic polyangiitis in chronic renal replacement therapy.

BACKGROUND: Pauci-immune vasculitis is a heterogeneous disorder with an unfavourable prognosis. Renal involvement is frequently observed in antineutrophil cytoplasm autoantibody (ANCA)-associated small-vessel vasculitis and is an important cause of end-stage renal disease (ESRD). Renal replacement therapy (RRT) is frequently required. Although better prognosis under dialysis is well known, the long-term follow-up of pauci-immune renal vasculitis with RRT is rarely reported. METHODS: We described 24 patients with pauci-immune vasculitis and requirement of dialysis who were admitted in our institutions from January 1989 to December 2008. Mean age was 65 ± 12 years at the beginning of dialysis. There were 12 males and 12 females. Patients with Wegener's granulomatosis, Churg-Strauss syndrome or evidence of anti-glomerular basement membrane were excluded. The study group was formed by patients with a diagnosis of necrotizing extracapillary glomerulonephritis and microscopic polyangiitis. RESULTS: The distribution according to ANCAs was 14 p-ANCA (58%), 5 c-ANCA (21%) and 5 ANCA-negative (21%) pauci-immune renal vasculitis. Pulmonary renal syndrome (PRS) was observed in 10 patients at the onset of vasculitis. Corticosteroids and daily cyclophosphamide were administered to 18 patients, and one patient had intravenous cyclophosphamide. Five patients received isolated corticosteroid therapy. Early reduction in cyclophosphamide dosage was required in five patients due to leucopaenia. Mean follow-up after first dialysis was 89 ± 66 months (range 2-208). Twenty patients were included in haemodialysis (HD), and four patients were included in peritoneal dialysis (PD). At the end of the study, nine patients had received a cadaveric kidney transplant (KT). Relapses rate after the onset of dialysis was 0.03 episode/patient/year. PRS-associated relapses after beginning dialysis were observed in four patients. Main therapy in relapses was also corticosteroids and cyclophosphamide. Survival rates for year 1, 2 and 5 was 91%, 91% and 85%, respectively. Overall mortality at the end of the study was 31.8%. Five patients died in the PRS group, but only one death was associated with progressive pulmonary fibrosis. Higher mortality was observed in PRS vasculitis present at the onset of RRT (50% vs 16.7%, P = NS). Better outcome in patients who received a renal transplantation was observed (88.8% vs 53.8%, P = NS). Conclusions. Despite a low number of patients in this series, pauci-immune vasculitis prognosis under dialysis seems equal to other causes of chronic kidney disease. This study observed a low rate of relapses after beginning dialysis. Poor prognosis is related to severe complications at the beginning of RRT. Today, kidney transplantation is an important therapeutic option for these patients.

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.

Salvage of accidentally sectioned peritoneal catheter: report of three cases.

Peritoneal dialysis (PD) accounts for 6% of patients on maintenance dialysis. There are several factors responsible for this low prevalence. Transfer of patients to hemodialysis when any problem in the technique is present is probably one of the most frequent reasons. Thus, when a problem in the PD catheter appears they are routinely removed instead of subjecting to salvage procedures. We report three cases of accidental cutting of the peritoneal catheter and present the steps taken to salvage the catheter without discontinuing the technique and avoiding withdrawal of the catheter.

Achieving chronic kidney disease treatment targets in renal transplant recipients: results from a cross-sectional study in Spain.

BACKGROUND: Kidney transplant recipients are considered to have chronic kidney disease (CKD) irrespective of glomerular filtration rate (GFR) or presence or absence of markers of kidney damage. The aim of this work was to investigate the prevalence of CKD-stages and whether the guidelines for general population (Kidney Disease Outcomes Quality Initiative) are routinely followed in kidney transplant in Spain. PATIENTS AND METHODS: Two thousand one hundred sixty renal transplant recipients followed up at the outpatient clinics in 4 University Hospitals were included. The estimated GFR (eGFR) was calculated according to the abbreviated modification of diet in renal disease equation, and the patients were classified following the Kidney Disease Outcomes Quality Initiative stages. RESULTS: Chronic kidney failure (eGFR <60 mL/min/1.73 m) was present in 1505 patients (69.7%), 54.4% were 3T-stage (eGFR 30-59); 13.0% were 4T-stage (eGFR 15-30), and 2.3% were 5T-stage. The prevalence of severe anemia increased from 4.1% in 1T-stage to 44% in 5T-stage (P=0.000) as did the percentage of patients on erythropoiesis-stimulating agents from 1.3% to 68% (P=0.000). The intact parathyroid hormone levels increased as graft function declined and 45% of 5T-stage patients had intact parathyroid hormone levels more than 300. Calcium and vitamin D supplements were administered to 50% and 40% of patients, respectively. Hypertension was quite common and increased with the progression of CKD. The mean total cholesterol was 192+/-39 mg/dL, and the levels did not increase with the decline in graft function. Approximately 60% had suboptimal cholesterol despite 50% being on statins treatment. CONCLUSIONS: CKD and their complications were prevalent in renal transplant recipients. The control of some of these complications is far below targets established for nontransplant CKD patients despite a progressive intensification of therapy as graft function declines.