Overcoming of One More Pitfall in Boundary Element Calculations with Computer Simulations of Ion-Selective Electrode Response.

Computer simulations of ion-selective membrane electrodes using diffusion layer models based on finite-differences principle for calculating diffusion processes in both phases and taking into account the local ion exchange equilibrium at the interface are successfully used for clarifying and even predicting the influence of different diffusion factors on several time-dependent characteristics of electrodes. It is shown here that a well-established approach based on the assumption of the constant concentration of the interfering ion in the sample solution fails for solutions containing strongly interfering ions where the concentration of the interfering ion in the boundary layer of the solution can be far lower in comparison with its concentration in the bulk. The limitation is demonstrated by a drastic discrepancy between experimental and calculated curves for the dependence of potential on time.

Application of the interface equilibria-triggered dynamic diffusion model of the boundary potential for the numerical simulation of neutral carrier-based ion-selective electrodes response.

It is shown that a simple dynamic diffusion model of the boundary potential based on a separate, step-by-step, account of ion transfer across the membrane/aqueous solution interface and the diffusion processes within both phases which was proposed earlier for describing the response of ionophore-free membranes, can be successfully used for ionophore-based membranes as well. The model makes it possible to carry out both separate and joint account of the effects of co-extraction, transmembrane transport and ion exchange on the boundary potential and retains robustness in all the variants studied. The model adequately describes the ionophore-based electrode response over the entire range of concentrations and allows one to clearly demonstrate the dependence of lower detection limit on such parameters as the diffusion coefficients and the concentration of electroactive substances in the membrane phase, the thickness of the diffusion layer in the sample solution, the duration of the measurement, and the composition of the internal reference solution.

An Interface Equilibria-Triggered Time-Dependent Diffusion Model of the Boundary Potential and Its Application for the Numerical Simulation of the Ion-Selective Electrode Response in Real Systems.

A simple dynamic model of the phase boundary potential of ion-selective electrodes is presented. The model is based on the calculations of the concentration profiles of the components in membrane and sample solution phases by means of the finite difference method. The fundamental idea behind the discussed model is that the concentration gradients in both membrane and sample solution phases determine only the diffusion of the components inside the corresponding phases but not the transfer across the interface.

[Comparative analysis of Fourier-transform infrared spectra in normal and malignant stomach tissues].

New data have been reported on Fourier-transform infrared spectra in 97 samples of resected material taken from normal and malignant tissues of the human stomach. Malignant tissues revealed a significant drop in peak intensity of vsPO2 bands (approximately 1089 cm-1) of nucleic acids characterized by the prevalence of high-frequency vCH3/ vCH2 protein and lipid fragments, the narrowing of vC=O bands of phospholipids, the simultaneous growth and narrowing of amide-I and amide-II bands, an increased homogeneity of the spectra, etc. Statistical data on the differences in normal and malignant tissue samples and diagnostically relevant criteria are presented.

[Causes of recurrence of pain in patients after cholecystectomy and its treatment].

The authors analysed the results of diagnosis and treatment of the postcholecystectomy syndrome in 131 patients. Recurrence of biliary colic after cholecystectomy is linked in most patients with functional disorders of the sphincter of Oddi (27.4%) which disappear in many cases after cholecystectomy.