Determination of lead ions using an diantipyrylmethane-based electrode

The possibility of using diantipyrylmethane as an ionophore component of a lead-selective electrode membrane was assessed. Membrane composition (wt %) was optimized: polyvinyl chloride (31.89), dioctyl sebacate (63.81), diantipyrylmethane (2.50), and oleic acid (1.80). The proposed model of the electrode works in the concentration range of 1 × 10^–5–0.1 M with a detection limit of 2 mg/L. A slope of the electrode function of the diantipyrylmethane-based electrode is 29.4 ± 0.5 mV/pPb. Concentration of Pb(II) ions in various samples was determined.     

Determination of tri- and tetravalent ions with a divalent ion-selective electrode

A method of determining tri- and tetravalent ions with a divalent ion-selective electrode is proposed. The determination is based on displacement of the divalent metal ion from the Mg-EDTA or Zn-EDTA complex. The approximate ranges for direct measurement are 3·10^-3–3·10^-4M. Titrimetric methods are recommended for analysis of mixtures of metal ions. Optimal pH ranges and precision are discussed.     

The determination of lead in water and sediment samples using a lead ion-selective electrode

Lead concentrations in water and sediment samples near a stationary metal emission source were determined using the lead ion-selective electrode. These results were then verified by use of atomic absorption spectrophotometric methods. Samples were collected at three strategic sites near a local lead company in Southeast Houston, Texas. Accumulated rain water and sediment (soil deep down core) were analyzed in order to estimate lead concentration as a function of depth. Data indicate that the level of lead concentrations in both surface water and water extracted from the sediments exceed the limits for drinking water as established by the Environmental Protection Agency. The lead concentrations of the soil samples were higher in most cases when compared with various soils in the United States. The highest concentrations of lead were found in surface water samples.     

Determination of sulfur in cosmetic products using ion-selective electrode

A method for the indirect voltammetric determination of sulfur is proposed. A solution of hydrazine hydrate was used as an alkaline medium to transform sulfur into sulfide. The optimal conditions were chosen for sulfur determination using ion-selective electrode and the results agree with those obtained by high-performance liquid chromatography. The text was submitted by the authors in English.     

Studies on determination of fluoride in zinc and lead concentrates by using a fluoride ion-selective electrode

A modification of the potentiometric determination of fluoride has been developed, which allows use of aqueous fluoride standards in analysis of lead or zinc concentrates, instead of the need to use matrix-matching or standard additions.     

Flow-injection potentiometric determination of free cadmium ions with a cadmium ion-selective electrode

The determination of free cadmium ions with solid-state cadmium ion-selective electrode can be performed in non-flow measurements in non-buffered solutions in a wide concentration range down to pCd 10. In cadmium ion buffered solutions linear Nernstian response was obtained even down to pCd 12, which is lower, that expected based on calculation of cadmium solubility from the conditional solubility product. Interferences of trace amounts of Fe(III), Cu(II) and Pb(II) commonly present in natural waters in larger concentrations than Cd(II) can be eliminated by reduction with hydroxylamine, complexation with Neocuproine and ion-exchange on anion-exchange resin in sulphate form, respectively. The developed procedure might be suitable for the determination of activity of free cadmium ions in natural water. A preliminary study on this subject is demonstrated for river water sample using stopped-flow flow-injection system.     

Microdetermination of secondary aliphatic amines using a copper ion-selective electrode

A simple, accurate, and selective method is described for the microdetermination of aliphatic secondary amines. The method is based on their reaction with carbon disulfide and ammoniacal copper sulfate at 40 °C for 30 min to yield copper dialkyldithiocarbamate. The excess copper is then measured by titration with EDTA or NaDDC using a copper ion-selective electrode. A mean recovery of 98.2% with a standard deviation of 0.8% is obtained for aliphatic secondary amines and their salts having a wide range of pK_a.     

Determination of nitrate in water with a new construction of ion-selective electrode

A new design of the liquid-state electrode for nitrate ions is proposed. It contains a porous wick soaked with the liquid ion-exchanger, and has no internal reference solution. This electrode was used for nitrate determination of tap water at the level 8–10 p.p.m. The effects of chloride and hydrogencarbonate are eliminated by the addition of silver sulphate and a phosphate buffer, which also maintains constant ionic strength. Precision of a series of measurements is better than 2%, but the results show differences up to 10% compared to the colorimetric brucine procedure.     

Determination of ion-selective electrode characteristics by non-linear curve fitting

A simple practical method of determining potentiometric selectivity coefficients of ion-selective electrodes (ISEs) is described in which electrode characteristics (slope, potentiometric selectivity coefficients and cell constant) can be determined by fitting the experimental data obtained using the fixed interference (FI) method to an appropriate model by non-linear least-squares regression. The proposed method is simple to implement practically, and data processing can be easily achieved through use of the optimisation add-on, Solver, bundled with Microsoft Excel. The flexibility of the method is demonstrated by modelling the response of a valinomycin potassium-selective electrode with the Nikolskii-Eisenman equation and a recently proposed alternative to the Nikolskii-Eisenman equation for cases where the ionic charges on the primary and interfering ions are unequal.     

Determination of phosphate in hydroponic nutrient solutions using flow injection potentiometry and a cobalt-wire phosphate ion-selective electrode

The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of −(47.57±0.03) mV per decade and intercept of −(169.7±0.1) mV were obtained for four separate calibrations in the concentration range 5.0×10⁻⁴–1.0×10⁻² M H₂PO₄⁻. Anion corrections for interferences by Cl⁻, NO₃⁻ and SO₄²⁻ were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.±2–5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions.     

Trifluoroacetate ion-selective electrode

The trifluoroacetate ion-selective electrode was prepared by using the organic solvent solution of trifluoroacetate salt of crystal violet or tris(bathophenanthroline) iron(II) chelate.The response is linear over the activity range 10^?1 to 3 × 10^?5M, with a Nernstian slope 60 mV/activity decade at 29 °C. The interferences of divalent ions, chloride, fluoride and acetate ions are extremely low. Iodide interferes greatly.     

Point-of-need diagnosis of cystic fibrosis using a potentiometric ion-selective electrode array

The novel approach of using a micro-sensor array of miniaturised solid-state ion-selective electrodes to analyse sweat samples for sodium, potassium and chloride simultaneously is described. The array, incorporated into a miniature flow cell which is linked to a portable PC for data acquisition, constitutes a small, portable, and simple to use analytical instrument. Samples are passed through the flow cell and over the array and an immediate potentiometric response is obtained, which can be equated to the concentrations of sodium, chloride, potassium and other parameters in the sweat sample. Used here in conjunction with a Wescor Macroduct sweat sampling unit, it promises a much simplified, much less expensive procedure for sweat analysis than the procedures currently in common use.     

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.