Experimental verification of the properties of ion-selective electrodes for low concentration determination.

The influence of several ion-selective electrode properties on electrode response and selectivity at low concentration levels has been investigated experimentally. The properties investigated were the composition of inner electrode solution, the composition of the membrane, the presence of interfering ions in the sample, and the thickness of diffusion layer in the sample solution. All the results obtained confirmed theoretical considerations.

Topochemical investigation of ancient manuscripts.

Various modern instrumental techniques for surface analysis were applied for the non-destructive physicochemical examination of works of art. As samples, pieces of ancient manuscripts endangered by iron-gall ink corrosion were used. Surface characterisation of the morphology of the cellulose fibres within corroded and non-corroded parts of the manuscript performed by scanning electron microscopy (SEM) showed seriously damaged cellulose fibres in the written parts. The elemental composition of selected parts of the manuscript was determined by energy dispersive X-ray fluorescence analysis (EDX). A more detailed study of the paper surface was then performed by electron probe microanalysis (EPMA). This technique yields the morphological characteristics of the surface as well as element distribution maps over the written area of the investigated manuscript.

Determination of hafnium in air dust filters by inductively coupled plasma atomic emission spectrometry.

The procedure of hafnium determination in workplace air has been elaborated, which allows its determination at the level starting from 0.125 mg m(-3), which for a 400 1 sample corresponds to the requirement for maximal allowable concentration. The method is based on excitation of the mineralized filter containing the analyte in inductively coupled plasma.

Carbonate ion selective electrodes with trifluoroacetophenone derivatives in potentiometric clinical analyser.

Properties of six derivatives of 1-trifluoroacetylbenzene: [4-(n-butyl)- (1), 4-(n-hexadecyl)- (2), 4-dodecyloxy- (3), 4-(n-dodecylsulfonyl)- (4), N,N-dioctyl-4-trifluoroacetylbenzamide (5), octyl-p-trifluoroacetylbenzoate (6)] as neutral carriers for carbonate ion were examined and compared. The sensitivity towards carbonate ion was for (3) pH dependent. This eliminates (3) from practical applications in clinical analysis. When measuring CO(3)(2-) within the physiological range of human blood using as carriers compounds 1 and 2 the interference of chloride must be taken into account. In the case of carriers 4, 5, 6 this effect is negligible. Electrodes with membranes containing as carriers 2, 4, 5 and 6 were tested in an automatic potentiometric clinical analyser Microlyte 6, KONE. To avoid contamination by atmospheric CO(2) of three aqueous standards (TES, NaCl, NaHCO(3)), pH was adjusted by coulomeric generation of H(+) or OH(-) in a system devoid of carbon dioxide. Recovery of HCO(3)(-) calculated from measured CO(3)(2-) and pH, was investigated in a series of aqueous solutions and spiked bovine serum samples. The correlation between added and recovered concentration of HCO(3)(-) was linear with the intercept close to 0 and slope equal to 1 in aqueous solutions for all ligands and in bovine serum samples only in the case of ligand (2).

Determination of cobalt in blood using cathodic stripping voltammetry.

A method was developed to determine low levels of cobalt in whole blood, serum and plasma. Samples of blood (0.2 ml) were mineralized at 160 degrees C in the presence of concentrated nitric acid. Residual organic matter was destroyed by digestion using ultraviolet irradiation after dilution with water. The cobalt concentration was determined by catalytic cathodic stripping voltammetry (CSV) preceded by adsorptive collection of cobalt complexed with diphenylglyoxime (DPG). The optimized analytical conditions for the CSV analysis included a DPG concentration of 0.5 mumol l-1, 0.05 mol l-1 ammonium chloride buffer (pH 9.3), 0.15 mol l-1 nitrite, a deposition potential of -0.75 V, an adsorption time of 30-120 s and a negative potential scan using the differential-pulse modulation. The limit of detection was 40 pg of cobalt in 0.2 ml of blood, which was limited by the blank level of cobalt in the reagents after purification.

Urea sensors based on PVC membrane pH electrode.

Several procedures of urease immobilization on the surface of the polymeric membrane pH electrode with tri-n-dodecylamine as a neutral carrier were compared. The best results were obtained for the urea sensor with covalently bound urease. The sensor characteristics including the effect of buffer, pH and concentration and the effect of stirring rate are presented. These effects are in good agreement with theoretical expectations.

Bifunctionality of chemical sensors based on the conducting polymer polypyrrole.

Responses of polypyrrole based ion-selective chloride electrode were investigated in chloride and redox media. Bifunctional character of the potentiometric response of the polypyrrole films doped with chloride ions was observed being sensitive both to chloride ions and to the redox potential of the solution, however the redox response seems to predominate.

Coulometric titration in the study of metal ion-ligand equilibria.

The coulometric titration technique is applied to evaluation of stability constants of metal complexes with ligands which have protolytic properties. The validity of the procedure was checked by studying several well-known systems. The proposed method can be used with success when metal ions are not reduced at the working cathode. Constants for calcium and magnesium complexes with components of some biologically important buffers, so-called Good buffers, were evaluated under experimental conditions (ionic strength of 0.16M, 37 degrees ) used in clinical analysis.

Potentiometric study of end-point detection in the coulometric determination of carbon dioxide.

The coulometric determination of carbon dioxide is based on the alkalimetric titration of the product of absorption of carbon dioxide in an organic solution of monoethanolamine. The processes occurring in various solvents have been investigated and optimized for analytical application. The protolytic reactions of 2-hydroxyethylcarbamic acid have been investigated in 2-propanol + 2, 5 and 10% water, dimethylformamide + 2% water, dimethylsulphoxide +5, 10 and 20% water. In coulometric generation of the base, 0.1M solutions of tetraethylammonium bromide in these solvents were used. The course of the titration was followed potentiometrically with glass and antimony indicator electrodes. From the titration curves the autoprotolysis constants of the mixed solvents and protonation constants of monoethanolamine in them were calculated. These constants and the concentration of monoethanolamine influence the size of the end-point break for the titrations. On this basis, optimal conditions for analysis have been selected and the total carbon content in samples of natural waters has been determined.

Interpretation of the selectivity and detection limit of liquid ion-exchanger electrodes.

An equation has been derived which describes the e.m.f. of a liquid ion-exchanger membrane electrode in conditions of low concentration levels of the primary and interfering ions. The equation is based on the assumption that if the external solution contains no excess of ions which may exchange with the organic phase, then the concentration of the exchanger at the interface decreases, and this is responsible for formation of a diffusion layer inside the membrane. Therefore the potential response depends on the initial concentration of the ion-exchanger in the membrane phase, on the thicknesses of the diffusion layer on both sides of the interface, and on the diffusion coefficients of the species in both phases. This equation explains the non-Nernstian behaviour of the electrode in the presence of interferents, as well as the variation of the conditional selectivity coefficients. The parameters mentioned also influence the detection limit of an electrode. The electrode behaviour has been tested in unstirred solutions and in solutions stirred at different rates. Through its influence on the diffusion layer thickness, the stirring also influences the electrode potential and the characteristics of the electrode.

Behaviour of a chalcocite copper ion-selective electrode in solutions of iron(III) ions.

The effect of iron(III) ions on the potential of the chalcocite electrode was investigated. Linear graphs were obtained for pFe(III) = 2-4, and were suitable for analytical purposes. The effect of ligands complexing iron(III) was studied, and the potential shown to be due to the concentration of free iron(III) ions only. The pH effect is mainly connected with solution reactions. A mechanism of potential response, based on a redox reaction, has been postulated, but the response does not depend on the redox potential in the bulk of the solution.

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.

Anionic interferences with copper ion-selective electrodes chloride and bromide interferences.

The effect ofhalide ions on copper ion-selective electrodes is connected with complexation and redox reactions, with the formation of amorphous sulphur, which by blocking the surface causes instability of potential response. It may be eliminated by addition of sodium thiosulphate solution. The electrode behaviour has been explained on the basis of the diffusion model. An equation is proposed for linearization of the calibration curve. The parameters of the semiempirical model which describes the electrode behaviour agree well with the physical meaning presented by the diffusion model. The treatment given enables analytical measurements of copper concentration to be made even in the presence of significant concentrations of chloride or bromide.

Variability of selectivity coefficients of solid-state ion-selective electrodes.

The generalized model for the selectivity mechanism of solid-state ion-selective electrodes has been experimentally verified. The experimental parameters investigated were the concentration of interfering ion, temperature and stirring. Among the systems studied were electrodes sensitive to chloride (bromide, iodide), bromide (chloride, iodide), iodide (chloride, bromide), silver (copper, lead), copper (silver, lead) and lead (silver, copper), the species given in brackets being considered as the interferents. The model has been confirmed except for cases where the concentration of ions formed at the electrode surface by metathesis is too small to be the factor that dictates the electrode potential.

A potassium-selective electrode with solid internal contact.

The performance characteristics of potassium-selective electrodes made with valinomycin membranes plasticized with dioctyl adipate or sebacate, and with a solid silver contact or an internal solution, have been critically examined. The choice of electrode depends on a number of factors, including the interfering ion(s) present. The electrodes can be used for determination of potassium in natural waters.

Influence of some matrix elements on atomization of cobalt in graphite-furnace atomic-absorption spectrometry.

The influence of some chlorine, sulphur and phosphorus compounds on cobalt atomization in a graphite cuvette has been investigated. On the basis of atomization curves and estimated atomization energies the mechanisms of several processes have been proposed. Excess of chlorine is responsible for losses of cobalt as chloride and also for formation of a compound with graphite which causes atomization to occur at a temperature 300 K higher than that in the absence of graphite. In presence of sulphur, the atomization goes through sulphide formation but a reaction with graphite is also suspected. The presence of phosphorus significantly increases the rate of atomization, which enhances the peak height for cobalt. The mechanism probably involves dissociation of phosphate salts.

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.

Effect of halogenated solvents on iron atomization in graphite-furnace atomic-absorption spectroscopy.

When an iron solution in an organic solvent is examined by atomic-absorption spectroscopy, the signal decreases to below that for a comparable aqueous solution. This effect is most pronounced for halogen-containing solvents because of volatility of FeCl(2), and a change in the atomization curve with a shift towards higher temperatures for atomization. When the cuvette is pretreated with halogenated solvent a double peak is observed. The first peak corresponds to that found for aqueous solvents, the second may be correlated with the peak for iron in a halogenated solvent. The peaksplitting effect of such a solvent increases with halogen:hydrogen ratio in the solvent. The halogen penetrates the structure of the graphite cuvette and probably forms strong carbon-haloge. compounds which modify the atomization conditions for iron. When water is introduced hydrogen halide is formed, which removes the excess of halogen from the atomization region.