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Klára Tóth

Publications and source records attributed to Klára Tóth.

6 recordsLinked to original sources
PubMed2006

How to assess the limits of ion-selective electrodes: method for the determination of the ultimate span, response range, and selectivity coefficients of neutral carrier-based cation selective electrodes.

The span and range of an ion-selective electrode (ISE) has been identified by IUPAC as a potential or activity difference between the upper and lower detection limits of the electrode. Once the span is known, the ultimately attainable detection limit of the ISE can be calculated using its theoretical response slope. In this paper, we propose an original method for the determination of the ultimate span and response range of ISEs. The simple measurement of span is recommended to aid the fast screening of novel ionophores and help to focus optimization processes to the most promising candidates. The measurement of span is combined with a generally applicable procedure for the determination of the three seminal parameters of ISEs: the response slope, the ultimate selectivity coefficients, and detection limit. In the proposed procedure, following the span measurement, two subsequent exponential dilution experiments are completed in which the responses of the electrode for the primary and the interfering ions are tested using a solution of a discriminated ion and deionized water as diluting electrolytes in consecution. The advantages and the practical usefulness of the proposed methods and procedures are demonstrated through the evaluation of the performance characteristics of novel and well-characterized ionophore-based potassium and calcium sensors.

Calcium↗
PubMed2005

Spectrophotometric determination of the dissociation constants of crown ethers with grafted acridone unit in methanol based on Benesi-Hildebrand evaluation.

As potential chromo- and fluorophores for optical sensors a number of acridone grafted crown ethers containing NO2 group(s) and/or Br or Cl atom(s) in the aromatic rings (compounds) were studied by spectrophotometric method. In the first step of this work the acid-base and complexing properties of these compounds as well as those of the acridone, thioacridone and 4,5-dinitroacridone were investigated. Compounds proved to be very week acids and therefore the conventional spectrophotometric method based on the measurement of the ratio of the protonated/deprotonated forms of the compounds was not applicable for the determination of the dissociation constants (pKa values). Thus, a new spectrophotometric approach was elaborated for the pKa determination of these compounds, which is based on spectrophotometric titration in methanol with strong base and the titration results were evaluated by the Benesi-Hildebrand method. (In the studies with TEAOH, TMAOH and LiOMe, the complex formation between the ionophores and the cations of the bases could be excluded.) As it was expected, the experimentally determined pKa values depended on the nature of the substituents of the acridone moiety and pKa values ranged between 12.6 and 14.9. The lower pKa value of thioacridone compared to the acridone can be explained by the larger size of the sulfur atom. The outstandingly larger pKa value for 4,5-dinitroacridone can be attributed to the formation of intramolecular hydrogen-bonds between the ortho-position nitro group and the NH proton. As a trend, the strong electron withdrawing nitro substituents decreased considerably the pKa values of compounds and compared to that of the halogen (Cl and Br) atoms (for example compounds and) of weaker withdrawing effect.

Acridines↗
PubMed2005

Interaction of dopamine and acetylcholine with an amphiphilic resorcinarene receptor in aqueous micelle system.

The molecular recognition of neurotransmitters, dopamine and acetylcholine with an amphiphilic resorcinarene receptor was investigated in an aqueous sodium dodecylsulfate (SDS) micelle system by 1H NMR measurements. The interaction distances of these neurotransmitters from the hydrophilic cavity of the amphiphilic receptor were estimated based on the calculation of the ring current shift using the atomic coordinates obtained from molecular dynamics calculation.

Acetylcholine↗
PubMed2004

Synthesis and characterization of covalently immobilized bis-crown ether based potassium ionophore.

The synthesis of a novel covalently immobilized crown ether based potassium ionophore is presented. Apart from previously proposed methods for the preparation of PVC linked ionophores based on the chemical modification of functionalized PVC polymers, the hereby proposed procedure involves the direct copolymerization of a suitable derivative of the bis-crown ether type potassium ionophore (BME 44) and vinyl chloride monomer. The analytical performance of the potentiometric ion selective electrodes incorporating the PVC bound ionophore were optimized and determined. Compared with electrodes based on other bis-crown ether type immobilized potassium selective ionophores a slightly improved logK(K, Na)(Pot) and a longer lifetime was found. Spectral imaging and chronoamperometry were used to study the mobility of different bis-crown ether derivatives in plasticized PVC membranes.

Crown Ethers↗
PubMed2003

Optical biosensor for urea with improved response time.

An optical biosensor for urea measurements was developed. The operation of the sensor is based on the well-known urease enzyme-catalyzed hydrolysis of urea. The ammonium ions liberated in the reaction are detected with an ion selective optode membrane containing nonactin as ion selective ionophore and ETH 5294 chromoionophore in a thin (1 microm) plasticized poly(vinylchloride) film. The basic sensing element was home made of a microscope glass slide, a HeNe laser light source, photodiode light detector and light in coupling, de-coupling elements. The transducer membrane and the enzyme containing reaction layer were sandwich-cast with spin coating onto the surface of the sensing slide. The attenuation of the laser light propagating inside the glass wave-guide was used as signal for urea measurements. With this arrangement membranes provided good sensitivity (0.05 absorption unit when going from 0.1 to 1 mM urea) and short (16-20 s) response time. Taking advantage on the improved response time, flow injection urea measurements were made in the 0.01-2 mM concentration range. Thirty sample/hour analysis-rate, good peak-to-peak reproducibility (RSD=0.02) and recovery (95-104%) was achieved with buffer diluted urea solutions. Applications for the analysis of real samples are planned to do in the future.

Biosensing Techniques↗