Adam Hulanicki

Complexation reactions of dithiocarbamates.

The complexation reactions of various disubstituted dithiocarbamates are discussed. Special attention is paid to studies of composition and stability of various metal complexes. The conditions of complex formation in solution are treated in terms of side-reaction coefficients. The properties of metal-dithiocarbamate complexes are presented as a function of the nature of the substituents in the ligand molecule.

CHEMICAL SENSORS DEFINITIONS AND CLASSIFICATION

A chemical sensor is a device that transforms chemical information, ranging from the concentration of a specific sample component to total composition analysis, into an analytically useful signal. The chemical information, mentioned above, may originate from a chemical reaction of the analyte or from a physical property of the system investigated.

Metal-Metal Oxide and Metal Oxide Electrodes as pH Sensors

The pH is one of the most important parameters for char-acterizing the chemical properties of an aqueous solution. The glass eiectrode is by far the most commonly used pH sensor. The determination of pH in special situations, e.g., in vivo applications where the fragility of the glass electrode is a draw-back, requires pH sensors that can easily be miniaturized and built into physically rugged sleeves. Also, for other applications where the volume of solution is very restricted miniaturization of pH sensors is very important. The glass electrode does not respond properly to pH in some corrosive environments (e.g., in hydrogen fluoride [HF] solutions). At present, among alternatives to the hydrogen-selective glass electrode group of sensors, potentiometric metal-metal oxide pH sensors respond to pH, ideally due to an equilibrium involving the metal and its oxide. In the case of metal oxide electrodes, the metal is not involved in the potential-determining reaction. This distinction is of course not clear in many cases because the mechanism giving the pH response is not always unequivocal.

All solid-state hydrogen ion-selective electrode based on a conducting poly(pyrrole) solid contact

A potentiometric ion-selective electrode based on a solid conducting poly(pyrrole) contact and neutral carrier tri-n-dodecylamine membrane was developed. The effect of the poly(pyrrole) doping anion on the characteristic of the sensor is presented and discussed. The ion-selective H+ sensitive electrode with a solid poly(pyrrole) contact is characterized by having a good stability over both short and long periods of time. Selectivity coefficients for this electrode are slightly better than those for internal solution electrodes. Stability is also improved especially when compared with coated wire type electrodes. Responses are fast and nearly Nernstian within the pH range 2–12. All solid-state sensors with plastic tri-n-dodecylamine were used for pH determinations in blood serum.

Ion-Exchange Preconcentration and Separation of Trace mounts of Platinum and Palladium

ABSTRACT The preconcentration and separation of platinum and palladium from weakly acidic solution (pH=4) were done on microcolumn packed with Cellex-T resin. Selective platinum elution from the column was performed with 0.01 mol/l glycine solution at pH=12, while for palladium elution 1.2 mol/l thiourea (pH=0.5) or 4.0 mol/l potassium thiocyanate (pH=1) may be used. As the detection technique was used either FAAS or GFAAS, depending on the concentration of studied metals in the eluate.

Noble metals as permanent modifiers for the determination of mercury by electrothermal atomic absorption spectrometry

Palladium, gold, rhodium and iridium have been investigated as chemical modifiers for mercury determination by ETAAS. The gold/rhodium mixture and palladium alone, thermally reduced in the graphite tube, and also electrodeposited palladium give the best analytical performance. Under those conditions a characteristic mass of 110 pg is obtained for mercury. The amount and the reduction temperature of the modifier, together with the pyrolysis, atomization and cleaning temperatures for mercury have been optimized in order to find best conditions for permanent modification. Experimental conditions for palladium and rhodium after thermal and electrodeposition as a permanent modifier have also been optimized. It is shown that thermally deposited palladium can serve for about 50 firings when the maximum temperature does not exceed 1800°C. The tubes pretreated with a thermally deposited gold/rhodium mixture or electrodeposited palladium exhibit extended analytical lifetime (up to 500 firings without loss of sensitivity) even when tubes are heated up to 2000°C.

Flow-injection determination of nitrite and nitrate with biamperometric detection at two platinum wire electrodes

Abstract The flow-injection determination of nitrite is based on oxidation of iodide by nitrite. The triiodide formed is detected amperometrically in a flow-through cell with two teflonized graphite or platinum wire electrodes polarized with a voltage of 100 mV. More sensitive and faster response was observed with the platinum wire electrodes. The same detector is used for determination of nitrate after reduction to nitrite in a reductor column containing copperized cadmium. Detection limits under optimized conditions are 6 μg l −1 for both nitrite- and nitrate-nitrogen. Effects of oxygen and interfering metal ions are discussed.

Diffusion-layer model for copper solid-state chalcocite membrane electrode; sensitivity to copper(II) ions.

The diffusion-layer model for the chalcocite (Cu(2)S) membrane electrode is discussed. It is equivalent to a simpler model based on exchange reactions at the electrode surface. The chalcocite is sensitive to copper(I) and copper(II) ions and the theoretically predicted response is in good agreement with experimental data. The membrane is a conductor, but this does not significantly affect its function as an ion detector. The limitation of the electrode is the membrane solubility as shown when Cu(II) ions in contrast to copper(I) ions are strongly complexed.

Simultaneous determination of Se and As by hydride generation atomic absorption spectrometry with analyte concentration in a graphite furnace coated with zirconium

Abstract Conditions for the simultaneous determination of selenium and arsenic at ng l −1 level were developed. Simultaneous determination of these elements was possible through the multielement capabilities of hydride generation, with in situ trapping and atomization in a graphite tube coated with zirconium and measurements using a dual channel atomic absorption spectrophotometer. The zirconium coating employed in this work was relatively stable; once formed it could stand ≈80 firings without any significant change in the efficiency of hydride collection. This appears to be an advantage over the palladium coating, which is usually formed individually before each measurement because of its thermal instability during the atomization step of the furnace temperature programme. As a result, two determinations of the two elements could be performed in 2.5 min. Under the optimized conditions, concentration detection limits of 17 and 13 ng l −1 for a 7.1 ml sample volume were obtained for selenium and arsenic, respectively (absolute detection limits 120 and 92 pg for Se and As).

Urea sensors based on glass pH electrodes with physically immobilized urease

Abstract Different gels were used as a matrix for physical enzyme immobilization on the sensing surface o glass pH electrodes. The recommended technique of immobilization is based on enzyme entrapment within a gel prepared in situ on the glass electrode surface. Poly(vinyl chloride), cellulose trinitrate and especially cellulose triacetate are the best matrix materials of urease immobilization. The effect of buffer pH and buffer capacity and the effect of the stirring rate were investigated and the optimum measurement conditions are discussed.