Search PubMed⌕ Search

Biomedical subjects

Ernö Pretsch

Publications and source records attributed to Ernö Pretsch.

17 recordsLinked to original sources
PubMed2006

Potentiometry at trace levels in confined samples: ion-selective electrodes with subfemtomole detection limits.

We explore here for the first time the direct potentiometric detectability of calcium, lead, and silver ions in amounts on the order of 300 attomoles at 100 picomolar concentrations without any preconcentration, analyte recycling, or electrocatalytic signal enhancement. The results presented here place zero-current potentiometry among the most sensitive electrochemical methods available.

Calcium↗
PubMed2005

Ion-selective supported liquid membranes placed under steady-state diffusion control.

Supported liquid membranes are used here to establish steady-state concentration profiles across ion-selective membranes rapidly and reproducibly. This opens up new avenues in the area of nonequilibrium potentiometry, where reproducible accumulation and depletion processes at ion-selective membranes may be used to gain valuable analytical information about the sample. Until today, drifting signals originating from a slowly developing concentration profile across the ion-selective membrane made such approaches impractical in zero current potentiometry. Here, calcium- and silver-selective membranes were placed between two identical aqueous electrolyte solutions, and the open circuit potential was monitored upon changing the composition of one solution. Steady state was reached in approximately 1 min with 25-microm porous polypropylene membranes filled with bis(2-ethylhexyl) sebacate doped with ionophore and lipophilic ion exchanger. Ion transport across the membrane resulted on the basis of nonsymmetric ion-exchange processes at both membrane sides. The steady-state potential was calculated as the sum of the two membrane phase boundary potentials, and good correspondence to experiment was observed. Concentration polarizations in the contacting aqueous phases were confirmed with stirring experiments. It was found that interferences (barium in the case of calcium electrodes and potassium with silver electrodes) induce a larger potential change than expected with the Nicolsky equation because they influence the level of polarization of the primary ion (calcium or silver) that remains potential determining.

Diffusion↗
PubMed2005

Potentiometric sensor for the measurement of Cd2+ transport in yeast and plants.

Research on heavy metals, and especially on transport of Cd(2+), has attracted much interest during the past decade. An optimized Cd(2+)-selective electrode for the continuous potentiometric monitoring of Cd(2+) fluxes in biological systems is presented. The selectivity of the electrode for Cd(2+) was further improved, and it now has very good long-term stability. The utility of this simple and inexpensive method is demonstrated by studying the Cd(2+) transport with model organisms, such as the yeast Saccharomyces cerevisiae and Arabidopsis cell cultures, frequently used in plant science. Its lower detection limits in the presence of commonly used growth media for yeast and plant cells are improved by approximately three orders of magnitude and are 10(-10) and 10(-8)M Cd(2+), respectively. Control experiments using atomic absorption spectrophotometry confirm that the decrease in Cd(2+) activities in the cell cultures is indeed due to the uptake of these metal ions by the cells. Both model systems can be easily transformed; therefore, in combination with the new electrode, they are very promising tools for the investigation of any protein of interest that might be involved in Cd(2+) transport.

Arabidopsis↗
PubMed2005

Monolithic capillary-based ion-selective electrodes.

Poly(styrene-co-divinylbenzene)-based monolithic capillaries of an inner diameter of 200 mum and a length of 2-5 mm have been used to construct Ca2+-, Ag+-, and Na+-selective electrodes. The membranes consist of a solution of ionophore and ion exchanger in bis(2-ethylhexyl) sebacate or 2-nitrophenyl octyl ether, which are used as plasticizers in conventional PVC-based membranes. With capillaries of low porosity, the potentiometric responses down to 10(-8)-10(-9) M solutions do not depend on the composition of the internal solution, which indicates a strong suppression of transmembrane ion fluxes. Thus, no tedious optimization of the inner solution is required with monolith ISEs. The lower detection limits of Ag+- and Ca2+-ISEs are comparable to the best ones obtained earlier with optimized inner solutions. Additionally, a monolithic Na+-selective ISE has been obtained exhibiting a lower detection limit of 3 x 10(-8) M Na+. With monolithic capillaries of higher porosity and fused-silica GC capillaries, the transmembrane flux effects are noticeable but still significantly smaller than with conventional PVC membranes.

Calcium↗
PubMed2005

Potentiometric sensors for trace-level analysis.

This review summarizes recent progress in the development and application of potentiometric sensors with limits of detection (LODs) in the range 10(-8)-10(-11) M. These LODs relate to total sample concentrations and are defined according to a definition unique to potentiometric sensors. LODs calculated according to traditional protocols (three times the standard deviation of the noise) yield values that are two orders of magnitude lower. We are targeting this article at analytical chemists who are non-specialists in the development of such sensors so that this technology may be adopted by a growing number of research groups to solve real-world analytical problems.We discuss the unique response features of potentiometric sensors and compare them to other analytical techniques, emphasizing that the choice of the method must depend on the problem of interest. We discuss recent directions in sensor design and development and present a list of 23 sensors with low LODs, with references. We give recent examples where potentiometric sensors have been used to solve trace-level analytical problems, including the speciation of lead and copper ions in drinking water, the measurement of free copper in sea water, and the uptake of cadmium ions by plant roots as a function of their speciation.

Journal Article↗
PubMed2004

A polypyrrole-based solid-contact Pb(2+)-selective PVC-membrane electrode with a nanomolar detection limit.

Ion-selective electrodes (ISE) based on conventional plasticized PVC membranes with solid inner contact (SC) have so far had unsatisfactory lower detection limits. Here it is shown that electropolymerization of pyrrole in the presence of potassium hexacyanoferrate(II)/(III) on Pt results in adequate inner contact for SC-ISE. The nanomolar lower detection limit achieved with the Pb(2+)-selective PVC membranes investigated is comparable with values obtained with optimized internal solutions of liquid-contact ISE.

Electrodes↗
PubMed2003

Role of fulvic acid on lead bioaccumulation by Chlorella kesslerii.

To better understand the relationship between lead speciation and bioavailability in natural freshwaters, the interaction of lead with the freshwater alga Chlorella kesslerii was studied in the presence of the Suwannee River fulvic acid (SRFA). Special attention was paid to direct interactions of the fulvic acid on the algae, as well as potential physiological (membrane permeability and algal metabolism) influences. Lead-free ion concentration measurements were carried out using a novel ion-selective electrode. Pb uptake decreased in the presence of SRFA with respect to noncomplexed Pb, but uptake fluxes, cellular Pb, Pb bound to the transport sites, and total adsorbed Pb were all higher than predicted from Pb2+ activities, in accordance with the free ion activity model (FIAM). The discrepancies between the observed values and those predicted by the FIAM in the presence and absence of synthetic ligands increased with increasing concentration of SRFA. Several hypotheses were examined to explain the observed differences. No contributions of labile and/or hydrophobic Pb-SRFA complexes were found. Furthermore, direct biological effects, including variations in membrane permeability or algal metabolism, could not account for the observations. On the other hand, changes in the algal surface charge due to SRFA adsorption seemed to account, at least partially, for the observed increase in lead uptake in the presence of SRFA as compared to that corresponding to the same Pb2+ concentration in the presence of synthetic ligands.

Adsorption↗
PubMed2002

Rational design of potentiometric trace level ion sensors. A Ag+-selective electrode with a 100 ppt detection limit.

Submicromolar to picomolar lower detection limits have recently been obtained with various polymer membrane ion-selective electrodes by minimizing biases due to ion fluxes through the membrane. For the best performance, the compositions of the membrane and inner solution should be optimized for each application. Given the number of parameters to be adjusted, it has been difficult to find the best parameters for a target sample. In this paper, a much simplified and more practical steady-state model of zero-current ion fluxes is derived, which is based on measurable parameters. The model allows one to predict achievable lower detection limits for a membrane with given selectivities. It can also be used to predict the optimal composition of the inner filling solution for the measurement of samples with a known, typical ionic background. Selectivity coefficients of monovalent and divalent analyte ions required for desired detection limits in drinking water are calculated. As an application of the proposed general recipe, a silver-selective electrode is developed on the basis of the ionophore O,O''-bis[2-(methylthio)ethyl]-tert-butylcalix[4]arene. With the predicted optimal composition of the inner electrolyte, its lower detection limit is found to be 10(-9) M or 100 ppt Ag+ with an ionic background of 10(-5) M LiNO3, which is very close to the expected value.

Cations, Divalent↗
PubMedDate not supplied

Immobilization of biomolecules on polyurethane membrane surfaces.

Lipophilic polymer membranes incorporating binding sites are widely used in various potentiometric, amperometric, and optical sensors. Here, we report on the biofunctional modification of the surface of a Ca(2+)-selective membrane. A photoactivatable biotin derivative was synthesized and covalently immobilized on a soft polyurethane membrane. The modified polymer was characterized by X-ray photoelectron spectroscopy (XPS) as well as by potentiometric measurements. The selective binding of streptavidin by the photo-cross-linked biotin derivative was demonstrated. The surface coverage obtained with different experimental protocols was analyzed by autoradiography using [(35)S]-streptavidin. The new approach may significantly extend the scope of applicability of potentiometric sensors.

Autoradiography↗
PubMedDate not supplied

Automatic spectra interpretation, structure generation, and ranking.

A new rule-based spectra interpretation system is described. It directly processes spectral files generated by spectrometers. Its internal information representation and the simultaneous use of several spectroscopic methods allow for the achievement of both high reliability and good performance. For small and medium sized molecules, the new program is capable of automatically reducing the solution space to under 3%.

Journal Article↗