Eva Samcová

Ion amperometry at the interface between two immiscible electrolyte solutions in view of realizing the amperometric ion-selective electrode

This article reviews the development in ion amperometry at the interface between two immiscible electrolyte solutions (ITIES) in view of realizing the amperometric ion-selective electrode (ISE). The concept of polarizability of ITIES in a multi-ion system is outlined. Principle aspects of ion amperometry at ITIES are discussed including the use of amperometry as a tool for the clarification of the ion sensing mechanism, and for determining the concentrations of ions in the solution. The reference is made to recent amperometric measurements at the supported liquid membrane (SLM) and polymer composite liquid membranes (PCLM), which, together with the micro-hole supported ITIES, appear to be particularly suitable for realization of the amperometric ISE.

Determination of the spectrum of low molecular mass organic acids in urine by capillary electrophoresis with contactless conductivity and ultraviolet photometric detection--an efficient tool for monitoring of inborn metabolic disorders.

A mixture of 29 organic acids (OAs) occurring in urine was analyzed by capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C(4)D) and UV photometric detection. The optimized analytical system involved a 100 cm long polyacrylamide-coated capillary (50 μm i.d.) and the background electrolyte of 20mM 2-morpholinoethanesulfonic acid (MES)/NaOH+10% (v/v) methanol, pH 6.0 (pH is related to the 20mM MES/NaOH buffer in water). The LOD values obtained by C(4)D for the OAs which do not absorb UV radiation range from 0.6 μM (oxalic acid) to 6.8 μM (pyruvic acid); those obtained by UV photometry for the remaining OAs range from 2.9 μM (5-hydroxy-3-indoleacetic acid) to 10.2 μM (uric acid). The repeatability of the procedure developed is characterized by the coefficients of variation, which vary between 0.3% (tartaric acid) and 0.6% (5-hydroxy-3-indoleacetic acid) for the migration time and between 1.3% (tartaric acid) and 3.5% (lactic acid) for the peak area. The procedure permitted quantitation of 20 OAs in a real urine sample and was applied to monitoring of the occurrence of the inborn metabolic fault of methylmalonic aciduria.

Rapid monitoring of arrays of amino acids in clinical samples using capillary electrophoresis with contactless conductivity detection

CE with contactless conductivity detection has been used to separate 28 biogenic amino acids in a short capillary with an effective length of 18 cm. All the tested amino acids can be mutually separated in 0.5-10 mol/L acetic acid electrolytes. The time of analysis does not exceed 6 min and the LODs vary from 0.1 to 1.7 micromol/L. The CVs lie within the intervals 0.01-0.4% and 0.9-4% for the migration times and the analyte peak areas, respectively. The procedure has been successfully applied to the determinations of the whole amino acid spectra in blood plasma, urine, saliva and cerebrospinal fluid samples.

Rapid monitoring of mono- and disaccharides in drinks, foodstuffs and foodstuff additives by capillary electrophoresis with contactless conductivity detection.

A capillary electrophoresis (CE) procedure with contactless conductivity detection (C(4)D) has been developed for monitoring of neutral mono- and disaccharides in drinks and foodstuffs. The separation of a mixture of seven neutral saccharides (glucose, fructose, galactose, mannose, ribose, sucrose and lactose) employed a quartz capillary, 5 μm i.d., with an effective length of 18.3 cm, and 75 mM NaOH (pH 12.8) as the background electrolyte (BGE). The limit of detection (LOD) values obtained lied within a range from 0.4 μmol L(-1) for lactose to 0.9 μmol L(-1) for ribose, with a separation time shorter than 140 s. The procedure was successfully applied to determinations of saccharides in fruit juices, Coca-Cola, milk, red and white wines, yoghurts, honey and a foodstuff additive.

Ion and pore fluid transport properties of a Nafion® membrane separating two electrolyte solutions Part I. Kinetics of the proton and alkali metal cation transport

Abstract A theoretical model is developed to describe the impedance of two electrolyte solutions separated by a fixed-site ion exchange membrane. The total impedance is the sum of the solution and membrane impedances, each of which splits into a resistance and a Warburg impedance owing to the diffusion—migration ion transport in the solution. Kinetics of the ion transport across the membrane solution interface is taken into account by using Schlogls theory of membrane permeation. It is shown that the pore fluid flow can be responsible for the coupling between the kinetic and transport impedances. As a result, the Warburg coefficient of the membrane impedance is predicted to decrease when the ratio of the rate of the pore fluid flow (membrane permeability) and the ion transport in the membrane bulk and/or across the membrane|electrolyte interface increases. Impedance analysis can thus provide an insight into the pore fluid transport properties of an ion exchange membrane. Equilibrium impedance measurements are used to analyse the transport properties of a Nafion® 117 membrane in the presence of alkali metal cations and protons. The Warburg coefficient of the membrane impedance decreases in the sequence Li+> Na+> K+> Rb+ ≈ Cs+ > H+ and even becomes negative for last four ions, which indicates an increasing relative contribution of the pore fluid flow. An evaluation of the permeability coefficient of the Nation® membrane from the impedance measurements confirms that in the presence of Na+ or Cs+ ions the pore diameter is about 5 or 3 times smaller, respectively than in the presence of protons.

Determination of ammonia, creatinine and inorganic cations in urine using CE with contactless conductivity detection

CE with capacitively coupled contactless conductivity detection (C(4)D) was used to determine waste products of the nitrogen metabolism (ammonia and creatinine) and of biogenic inorganic cations in samples of human urine. The CE separation was performed in two BGEs, consisting of 2 M acetic acid + 1.5 mM crown ether 18-crown-6 (BGE I) and 2 M acetic acid + 2% w/v PEG (BGE II). Only BGE II permitted complete separation of all the analytes in a model sample and in real urine samples. The LOD values for the optimized procedure ranged from 0.8 microM for Ca(2+) and Mg(2+) to 2.9 microM for NH(4)(+) (in terms of mass concentration units, from 7 microg/L for Li(+) to 102 microg/L for creatinine). These values are adequate for determination of NH(4)(+), creatinine, Na(+), K(+), Ca(2+) and Mg(2+) in real urine samples.

A determination of submicromolar concentrations of glycine in periaqueductal gray matter microdialyzates using capillary zone electrophoresis with contactless conductivity detection

CE with contactless conductivity detection has been used to determine the glycine neurotransmitter in periaqueductal gray matter (PAG) of rats. The LOD for glycine has been decreased to a value of 0.2 μM by adding 75% v/v of ACN to the samples and increasing the sample zone introduced to a value of 20% of the overall capillary length. The repeatabilities of the analyte migration times and the zone areas amount to 2.1 and 2.7%, respectively. The optimized CE/contactless conductivity detection method makes it possible to determine the micromolar concentrations of glycine in PAG microdialyzates without the necessity of sample derivatization. It follows from a pharmacological study that a local inflammation initiated by an application of carrageenan increased the glycine concentration in the rat PAG seven times, compared with a control. The glycine level in PAG can be decreased and the pain suppressed by administering paracetamol.

Very fast electrophoretic determination of creatinine and uric acid in human urine using a combination of two capillaries with different internal diameters

A capillary system formed by combining 25 and 100 μm id capillaries was used in the short‐end injection mode to determine creatinine and uric acid in human urine. The separation was performed at an electric field intensity of 2.3 kV/cm. Creatinine was determined in a BGE with a composition of 20 mM citric acid/NaOH (pH 3.0), and uric acid was determined in 20 mM MES/NaOH (pH 6.0). Under these conditions, migration times of 12.2 s for creatinine and 8.6 s for uric acid were achieved. The LOD value is 2.4 mg/L for creatinine and 0.9 mg/L for uric acid; the RSD for the migration time varies in the range 0.7–1.1% (intra day) to 1.0–7.5% (inter day); RSDs for the peak areas equalled 3.4–4.0% (intra day) and 4.3–4.7% (inter day). The determined creatinine values in seven urine samples vary in the range 221–1394 mg/L for creatinine and 87–615 mg/L for uric acid. t‐Test did not reveal any statistically significant difference between the developed CE methodologies and reference methods – Jaffé reaction for creatinine and enzymatic uricase test for uric acid.

The use of capillary electrophoresis with contactless conductivity detection for monitoring of glycerol in adipose tissues during a sporting performance

A CE procedure employing capacitively coupled contactless conductivity detection has been developed for direct determination of the glycerol and mannitol polyalcohols in biological and pharmacological samples. Both glycerol and mannitol are fully separated from the sample matrix within very short times of 3.0 and 3.9 min, respectively, when using the optimized BGE, 60 mM H3BO3+30 mM LiOH (pH 9.1). The LODs amount to 0.5 μM for glycerol and 0.3 μM for mannitol. The repeatability of the glycerol determination in real biological materials is characterized by the coefficient of variation values, 0.5 and 3.2%, for the migration time and the peak area, respectively. The procedure has been used to monitor the free glycerol concentration in adipose tissue microdialyzates. A physiological study has demonstrated that the lipolysis occurring during a sporting action can be stimulated by local application of adrenaline. The procedure has further been utilized to determine mannitol in a pharmacological preparation.

Voltammetry of Protonated Anesthetics at a Liquid Membrane: Evaluation of the Drug Propagation

Voltammetric measurements are used to study the transfer of protonated forms of local anesthetics (procaine, tetracaine, prilocaine, bupivacaine, lidocaine, dibucaine) across a supported o-nitrophenyl octyl ether (o-NPOE) membrane. Ion diffusion coefficients and ion transfer potentials were obtained, which are comparable with those inferred from measurements at a water–o-NPOE interface. It is shown that the pharmacological potency of local anesthetics correlates with standard ion transfer potentials of their protonated forms. It is proposed that the drug propagation involves the transfer of the ionic rather than uncharged anesthetic across the cell membrane.