Stanisław Głab

CHEMICAL SENSORS DEFINITIONS AND CLASSIFICATION

A chemical sensor is a device that transforms chemical information, ranging from the concentration of a specific sample component to total composition analysis, into an analytically useful signal. The chemical information, mentioned above, may originate from a chemical reaction of the analyte or from a physical property of the system investigated.

Bienzymatic potentiometric electrodes for creatine and l-arginine determination

Abstract Ammonium-selective electrodes enzymatically sensitized for creatine and l -arginine are presented. Enzyme layers of these biosensors contain two enzymes: urease and, as a second enzyme, creatinase or arginase dependent on the analyte (substrate): creatine or arginine. The bienzymatic layer with such a composition sequentially converts the analyte into ammonium ions, which are detectable by the internal sensor. Monomolecular and bimolecular bienzymatic layers immobilized directly on the ammonium sensitive membrane were used. The covalent binding of enzymes to the matrix of the ion-selective membrane made of the carboxylated poly(vinyl chloride) was performed using carbodiimide and glutaraldehyde. The extremely thin enzyme layers are strongly bound and easily penetrable. Therefore the presented biosensors are stable and respond rapidly, t 95% varies from 1.5 to 4 min. The linear ranges of both biosensors were 0.1–30 mM and the detection limits were below 10 −5 M.

An examination of the palladium/palladium oxide system and its utility for pH-sensing electrodes

Abstract Monocrystalline and polycrystalline palladium has been used for the electrochemical examination of the palladium—palladium oxide system in aqueous solutions. Two different methods were used to prepare the electrodes, namely a thermal method of oxidation at high temperature and an electrochemical method. Electrodes prepared by the electrochemical method did not have a good pH response. The properties of the thermally prepared electrodes depend on the temperature at which the oxidation was made. The optimum temperature is 750°C. The temperature range studied was 450–870°C. Electrodes prepared by the thermal method show an almost theoretical slope in the pH range 2.5–8.

Kinetic model of pH-based potentiometric enzymic sensors. Part 1. Theoretical considerations

A theoretical, kinetic model for a pH-based potentiometric enzymic sensor has been developed. It has been shown that the response of these sensors is governed by the pH, the buffering capacity of solutions analysed, and also the stirring rate. This model takes into account the variability of the kinetics of the enzymic reaction. The final equation is presented in an algebraic form and can be used in both fitting and optimization procedures.

Comparison of pH-Membrane Enzyme Electrodes for Urea with Covalently Bound Enzyme.

Abstract pH-membrane electrode with tridodecylamine as a hydrogen-ionophore was used for construction of urea biosensors. Carboxylated PVC membrane matrix allowed covalent enzyme binding to its surface. Several methods of chemical enzyme immobilization were tested. Urea enzyme electrodes with extended life-time (about 2 months) were obtained. The sensors characteristics are in good agreement with theoretical expectations. The influence of the immobilization method on the stability of the prepared biosensors is discussed.

Autoprotolysis constants by coulometric titration

A procedure is described for the evaluation of autoprotolysis constants in which a strong acid is titrated with coulometrically generated strong base. A two-compartment cell is used, and the acid may be added as such to the solvent under study, or generated in situ in the cell. When a silver auxiliary electrode can be used, as with solutions containing bromide ion, a single-compartment cell may be used, which seems to give more accurate results because it avoids the errors caused by diffusion of solution through the diaphragm. The results for the constants obtained for ethylene glycol, for methanol and for water are in reasonable agreement with values in the literature.

Penicillin enzyme biosensors based on pH membrane electrodes

Abstract Several penicillin biosensors obtained by covalent binding of penicillinase directly to the surface of pH detectors are presented. Two types of pH electrodes were used: membranes with tridodecylamine, as hydrogen ionophore, incorporated in carboxylated polyvinyl chloride, and membranes made of aminated polyvinyl chloride without any ionophore. Short response time and high stability characterize all described biosensors. The effects of several parameters on the shape of the calibration curves of the biosensors are discussed.

Spectrophotometric bioanalytical flow-injection system for control of hemodialysis treatment

A spectrophotometric flow-injection analysis (FIA) system for monitoring clinical hemodialysis is demonstrated. The role of a dialysate urea detector incorporated in this bioanalytical system is played by an optical flow-through biosensor based on Prussian Blue film with chemically linked urease forming a monomolecular layer of the enzyme. This pH-enzyme optode-FIA system is useful for the selective determination of post-dialysate urea in the range of concentration corresponding to its level in real clinical samples (2-16 mmol l(-1)). This bioanalytical system allows the analysis of about 15 samples of spent dialysate per hour. The operational and storage stabilities of the applied biosensor are longer than 2 weeks and 2 months, respectively. Clinical evaluation of the bioanalytical system was performed.

Autoprotolysis constants and acid-base properties of propylene glycol mixtures

The autoprotolysis constants of propylene glycol and its mixtures with water, acetone, propan-2-ol and chloroform have been determined potentiometrically. In the same solvent mixtures the protolysis constants of the phthalic acid-hydrogen phthalate system have been evaluated and indicate that the solvent is more acidic than water, but less acidic than ethylene glycol.

Determination of protonation constants by coulometric titration.

Application of coulometric titration to the determination of the protonation constants of acids and bases offers several advantages because of its simplicity, precision and accuracy. This procedure is rapid and requires only one calibration solution of strong acid in the same solvent and at the same ionic strength as the solution of acid (or base) being investigated. The procedure seems to be especially advantageous in the case of non-aqueous or mixed solvents having amphiprotic character. The validity of the method has been checked with several substances in water, 95% ethanol and ethylene glycol.