Ion-selective electrode for salicylate assay in blood serum

A salicylate-selective membrane electrode made with heptyl-4-trifluoroacetylbenzoate as a neutral carrier was successfully applied for the determination of salicylate in blood serum. This procedure is advantageous because the free concentration of the drug in serum can be determined without sample preparation. The free salicylate concentrations determined by the ion-selective electrode compared to those obtained by conventional colorimetry gave a linear correlation coefficient 0.997 in the salicylate concentration range 0.1-2.5 mM.     

Determination of urea in blood plasma by enzyme-pH electrode

Combination of gel-entrapped urease with a pH electrode can be used to measure plasma urea, provided that the response is related to an auxiliary pH electrode. The response time is 1–3 min and electrodes can be used for up to one week. Good correlation was obtained for routine samples with a spectrophotometric diacetyl monoxime method (y = 0.952x + 0.224, r = 0.996).     

Behaviour of the platinum electrode as a pH electrode

The platinum wire electrode behaves as a good pH electrode in the titration of 1.0 and 0.1N sulphuric or hydrochloric acid with the equivalent concentration of sodium hydroxide. The efficiency is greater when sulphuric acid is used. The end-points obtained are very close to those obtained with a glass-calomel system.     

Immobilized enzyme electrode for the determination of salicylate in blood serum

This determination of salicylate in blood serum is based on application of an immobilized enzyme electrode. Salicylate hydroxylase (E.C.1.14.13.1) is chemically immobilized onto a pig intestine mounted on an oxygen electrode. The signals are monitored amperometrically and the resulting output voltage is read using a simple adapter. The experimental parameters and possible interferences are discussed. Samples containing 1.0 × 10^?5?1.87 × 10^?3 M (1.6–300 μg ml^?1) salicylate were assayed with relative standard deviations between 1.3% and 6% and recoveries between 98.7 and 103%. Results obtained by the proposed method and by the established clinical method for randomly spiked pooled serum samples correlated well (r = 0.99).     

A novel dual-impedance-analysis EQCM system--investigation of bovine serum albumin adsorption on gold and platinum electrode surfaces

Both quartz crystal micro-balance (QCM) impedance and electrochemical impedance spectroscopy (EIS) methods are widely used in interface studies. This paper presents details about a new strategy for simultaneous, mutual-interference-free and accurate measurements of QCM impedance and EI, through connecting a suitable capacitance in series with the piezoelectric quartz crystal (PQC) between QCM impedance and EIS measurement instruments. Combined and individual measurements of QCM impedance and EIS during silver deposition gave results comparable with each other, demonstrating the reliability of the proposed method. Bovine serum albumin (BSA) adsorption on gold and platinum electrodes in Britton-Robinson (B-R) buffers was investigated, and the Fe(CN)6(3-)/Fe(CN)6(4-) couple was used as an electrochemical probe to characterize BSA adsorption. While the reversibility of Fe(CN)6(3-)/Fe(CN)6(4-) couple on bare Au and Pt electrodes changed very slightly with decreasing solution pH from pH approximately 7 to pH approximately 2, the standard rate constant (ks) of this couple increased abruptly with solution pH below pH approximately 4.5 at a BSA-modified Au electrode, but decreased with solution pH at a BSA-modified Pt electrode. By analyzing the QCM impedance data with a modified BVD equivalent circuit and the EI data with a modified Randle's equivalent circuit, inflexion changes at pH approximately 4.5 were all found at pH-dependent responses of the resonant frequency, the double-layer capacitance, the capacitance of the adsorbed BSA layer, the peak-absorbance values of BSA solutions at 277.5 and 224.5 nm, and so on. It was also found that a BSA adsorption layer can effectively inhibit gold corrosion during ferrocyanide oxidation in a ferrocyanide-containing BR solution. Some preliminary explanations of these findings have been given. The proposed method is highly recommended for wider applications in surface science.     

Neutral carrier-based Na+-selective electrode for application in blood serum

The ionophore N,N,N,N-tetracyclohexyl-1,2-phenylenedioxydiacetamide (4) shows higher lipophilicity and superior Na⁺/K⁺ selectivity than the previously described N,N-dibenzyl-N,N-diphenyl-1,2-phenylenedioxydiacetamide (2). It is a suitable component of Na⁺-selective liquid membrane electrodes for the assay of Na⁺ in clinical analysers.On leave from Hitachi Ltd., Central Research Laboratory, Kokubunji, Tokyo 185, Japan.     

Immobilization of enzyme to platinum electrode and its use as enzyme electrode

A glucose electrode was fabricated by immobilizing glucose oxidase covalently onto a platinized platinum electrode. The sensor showed rapid response with response time of 2—4 s, and also the linear response to the glucose concentration, ranging from 2 x 10^-3 to 5 mM. The sensitivity was found to be correlated with the surface area of a base electrode used.     

Ultramicrocoulometric determination of ammonia in serum, plasma, and blood

A method has been developed for the ultramicrodetermination of ammonia in as little as 0.01 ml of serum, plasma, or blood by coulometric titration with electrogenerated hypobromite using a sensitive amperometric endpoint. The only accurate volumetric measurement required is the pipetting of the sample. The sample is added to a 33-mm microdiffusion cell for 10 min to separate the ammonia; the ammonia is collected in 0.1 ml of 0.0025 M sulfuric acid in the center compartment. The separated ammonia is added to a coulometric generation cell where an excess amount of hypobromite has been generated. The decrease in amperometric current due to the utilization of the hypobromite by the ammonia is taken as a measure of the ammonia content; comparison is made with diffused standards. An optimum pH of 8.6 for the titration has been found to give reproducible results at all levels encountered. One-tenth-milliliter blood samples are routinely analyzed. When elevated ammonia levels are encountered, 0.01-ml samples can be used with accurate results. The time for the analysis is 10–15 min after initiating the diffusion.     

Characterization of diffusion-controlled mass transport through nanoporous and nanothin films plasma polymerized on a sputtered platinum electrode

We demonstrate the diffusion mode of various redox chemical species through a plasma-polymerized nanothin coating with nanometer-sized pores on a sputtered platinum (Pt) electrode. In this work, hexamethyldisiloxane plasma-polymerized films (PPFs) were added onto the sputtered platinum film, both of which were sequentially deposited in the same vacuum chamber. Results of atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemical studies showed that the PPF provided the platinum electrode with a coating with a complete surface coverage. Sub-nanometer-sized pores (less than 1 nm) responsible for a highly crosslinked polymer network in the PPF coatings offered diffusivity-controlled permeation of redox molecules (i.e., size-exclusivity) rather than solubility-controlled permeation (i.e., chemoselectivity). Consequently, variation of the plasma power could give control over the size of the nanometer-sized cavities.     

Enantioselective potential response of a human serum albumin-modified ITO electrode for tryptophan

The present study aims at extending the possibility of utilizing bulky molecules such as proteins for fabricating electrochemical chiral sensors using an indium tin oxide (ITO) electrode. Enantioselective potential response of the human serum albumin (HSA)-modified ITO electrode was observed for tryptophan (Trp) when HSA was immobilized on an ITO electrode surface modified with disuccinimidyl suberate (DSS). In this sensing system, the enantioselective interaction between HSA and Trp is detected through the chemically reactive DSS group immobilized on the ITO electrode.     

The mechanism of the platinum indicator electrode in argentometry

A study has been made of the behaviour of platinum and some other inert electrodes in silver nitrate titrations. Where the metal surface has been subjected to a reducing treatment, such as cathodic polarization, before use, the electrode will often function as a silver indicator electrode throughout the titration. It has been shown experimentally that this is due to the formation of a layer of metallic silver upon the electrode by interaction of the surface with silver ions in solution. If the metal surface undergoes such pretreatment that it is oxidized, then its potential normally remains at the oxide value during a silver nitrate titration until the silver ion concentration is sufficiently great for this value to be exceeded by the silver silver ion potential; formation of metallic silver then again takes place and from this point onwards the electrode behaves as a silver electrode. A detailed interpretation of the behaviour of platinum after various pretreatments has been made along these lines.     

Multi-electron oxidation of formaldehyde on a platinum electrode

The time evolution of a self-sustained potential oscillation under constant current oxidation of formaldehyde was observed on the rotating ring disk electrode assemble. Under the condition when the potential was controlled, the laser deflection voltammogram as well as the conventional cyclic voltammogram were measured. The mechanism of the multi-electron oxidationof formaldhyde on a platinum electode is discussed.     

Ionic strength-controlled virtual area of mesoporous platinum electrode

Mesoporous electrodes provide an unusual opportunity to observe the dramatic transition of the electrochemical potential distribution in vicinity to mesoporous surfaces as the ionic strength varies. The experimental results were in accordance with what the classical Gouy-Chapman theory predicts on the basis of the correlation between Debye length (kappa-1) and the diameter of mesopores. Using the phenomenon that the electrochemically effective area of mesoporous electrode depends on the ionic strength, the faradaic current density of dioxygen reduction could be controlled by the electrolyte concentration.     

Para-phenylenediamine oxidation at a platinum electrode in acetonitrile solutions

p-Phenylenediamine oxidation at platinum electrodes in acetonitrile solutions has been studied under a very wide range of experimental conditions. Chronopotentiometry, rotating disc electrode and cyclic voltammetry were used as electrochemical techniques. Coulometry at constant potential and product analysis were also performed.The electrochemical reaction appears as a fast and reversible one electron exchange per molecule of PPD. The electrode reaction is further complicated by follow-up chemical reactions giving unknown products in the bulk of the solution.The whole polarization curve under steady state conditions shows two waves, while under non-steady state conditions a small wave at intermediate potentials is also apparent.The reaction pathway for the first wave was interpreted as a non-conventional e.c.e. mechanism where the parent molecule acts as a base in the chemical step.These assumptions were confirmed through experiments performed with pyridine or water addition.     

Electrochemical reduction of decafluorobenzil in DMF on a platinum electrode

The mechanism of electrochemical reduction of decafluorobenzil on a platinum electrode in DMF was investigated by cyclic voltammetry. The first reduction peak corresponded to a reversible single-electron transfer leading to the formation of a relatively stable anion-radical whose ESR spectrum was registered and characterized. The second peak corresponded to the reduction of the anion-radical into an unstable dianion that quickly reacted with initial decafluorobenzil, and the arising species (or its transformation product) at the given potential underwent further reduction. The effect of fluorine on the potentials and on the mechanism of the electrochemical reduction of decafluorobenzil was considered.