Boris Pihlar

Cobalt and Copper Hexacyanoferrate Modified Carbon Fiber Microelectrode as an All-Solid Potentiometric Microsensor for Hydrazine

This article reports on the novel mixed cobalt and copper hexacyanoferrate (CoCuHCF)-modified carbon fiber cylinder microelectrode (CFCME) and its application to potentiometric determination of highly toxic hydrazine. The substrate CFCMEs were fabricated in a standard manner using carbon fibers of 7 µm in diameter. The CoCuHCF film was deposited electrochemically by cycling the potential between 0 and +1.0 V (vs. Ag/AgCl) in a solution containing the precursor salts. It exhibited good chemical stability in the pH range from 1 to 9. The effects of the coverage/thickness of the CoCuHCF coating, of the pH of a measurement solution, and of the activation of the sensor, on the potentiometric response to hydrazine were examined in detail. The potentiometric behavior of CoCuHCF film in the presence of hydrazine, with the potential (emf) slope of –55 mV/decade, was compared with those of four single metal HCF films (CoHCF, CuHCF, FeHCF, and NiHCF) prepared in the same way, and the possible role of the CoCuHCF film components is explored and discussed. The emf versus log CHyd calibration plot was linear over 3 orders of magnitude, from 1.0×10–6 to 1.0×10–3 mol/L, with a correlation coefficient of 0.995. The limit of detection was found to be 5×10–7 mol/L. The response times of 10 to 30 s and the temperature coefficients of ca–2.7 mV/°C were obtained at various hydrazine concentrations. The repeatability of measurements was very good with the relative standard deviation ranging from 3 to 4% (n=10), depending on hydrazine concentration. The selectivity of the reported microsensor was found excellent, except in the case of a few negatively charged interferents for which it was greately improved by an additional Nafion coating. The useful lifetime of the all-solid microsensor was found to be more than 2 months when stored in air.

Determination of total mercury in coal fly ash by gold amalgamation cold vapour atomic absorption spectrometry

Abstract A method for the determination of total mercury in coal fly ash by gold amalgamation cold vapour atomic absorption spectrometry (CV-AAS) was optimized. Most of the experiments were performed on NBS SRM 1633a Coal Fly Ash with a certified value of 160 ± 10 ng Hg g−1. The main attention was focused on the decomposition of the sample. The efficacy of pressure decompositions in closed silica and sealed Pyrex tubes using various combinations of acids (HNO3, HCl, HClO4) was compared with oxidative combustion of the coal fly ash. Notwithstanding the incomplete mineralization of the sample in sealed tubes, the results obtained showed good agreement with the certified value and results obtained by neutron activation analysis (NAA), which suggests that mercury is quantitatively released from the sample into solution. Lower results were obtained using decomposition in closed (but not hermetically sealed) silica tubes owing to losses of mercury by volatilization during decomposition. Interferences from some metal ions (nickel, lead, copper, silver, palladium, zinc and antimony) were also examined. The results showed a serious depression of the mercury signal only when gold, palladium and platinum were present at higher concentrations, which never or very seldom occur in fly ash matrices, and therefore do not represent a limitation of the method.

Optical, spectroelectrochemical and structural properties of sol-gel derived Ni-oxide electrochromic film

Abstract Ni-oxide films prepared using the sol-gel route and dip-coating method have been investigated by X-ray diffraction, scanning electron microscopy, FT-IR spectroscopy, cyclic voltammetry and in situ UVVIS spectroelectrochemical methods. The sols were prepared from a nickel sulphate hexahydrate precursor with formamide and polyvinylalcohol added to improve the abrasive resistance of films and to increase the yield from dip-coating deposition method (100–120 μm per dipping cycle). The films consisted of 40% NiO crystalline phase with an average grain size of 10 to 30 A. The crystallites were incorporated into the amorphous phase which was found to resemble the α(II)-Ni(OH)2 phase. A pronounced electrochromic effect (ΔT ≈ 60%) was found by cycling the films in a 0.1 M LiOH electrolyte. This produced a maximum colouration efficiency (λ = 450 nm) of 35–40 cm2 C−1. Longitudinal optical (LO) mode of films potentially cycled up to 200 times have been detected by near-grazing incidence angle (NGIA) FT-IR reflection-absorption spectroscopy. The results revealed that the as-deposited films are progressively transformed to the β(II)-Ni(OH)2 phase which is then converted to the β(III)-NiOOH phase during further potential cycling. The influence of foreign ions (SO2−4, CO2−3, OH−) on the development of persistent electrochromism and stability of films was established and discussed in detail.

Interactions of oxovanadium(IV) and the quinolone family member--ciprofloxacin.

The interactions of quinolone ciprofloxacin (cfH) and oxovanadium(IV) were studied by various methods. Green crystals of a complex [V(IV)O(cf)(2)(H(2)O)] were isolated and the molecular connectivities established, although the crystal structure was not perfectly refined due to the instability of the crystals. Based on a plausible interpretation of the data sets, two cf anions bidentately coordinate to a vanadyl cation through carboxylate and carbonyl oxygen atoms; in addition, there is a water molecule in the coordination sphere. Solution techniques (cyclic voltammetry, electronic and electron paramagnetic resonance spectroscopy, potentiometric measurements) confirmed the presence of various species in the solution, the composition of which strongly depends on the conditions in the system. The antibacterial activity of the complex against various microorganisms was tested and it was established that its activity is similar to that of free ciprofloxacin.

The influence of complexing agent and proteins on the corrosion of stainless steels and their metal components

The present work is devoted to the problem of biodegradation of orthopaedic implants manufactured from stainless steel. In vitro simulations of the biocompatibility of two types of stainless steel, AISI 304 and AISI 316L, and their individual metal components, i.e. iron, chromium, nickel and molybdenum, were carried out in simulated physiological solution (Hanks) containing complexing agents. Knowledge of the effects of the chemical and biological complexing agents, EDTA and proteins, respectively, on the corrosion resistance of a metal should provide a better understanding of the processes occurring in vivo on its surface. The behavior of stainless steels and metal components was studied under open circuit and under potentiostatic conditions. The concentration of dissolved corrosion products in the form of released ions was determined by differential pulse polarography (DPP) and atomic emission spectrometry using inductively coupled plasma (ICP-AES). The composition of solid corrosion products formed on the surface was analyzed by energy dispersive X-ray spectroscopy (EDS) and their morphology was viewed by scanning electron microscopy (SEM). The addition of EDTA and proteins to physiological solution increased the dissolution of pure metals and stainless steels. The effect of particular protein differs on different metals and alloys.

Evaluation of size-exclusion chromatography and viscometry for the determination of molecular masses of oxidised cellulose

The molecular masses of oxidised cellulose samples from two different sources were determined by size-exclusion chromatography (SEC) and viscometry. SEC was performed at room temperature using a cross-linked polystyrene-divinylbenzene column and 1% LiCl (w/v) in N,N-dimethylacetamide (DMAc) as the eluent. Cellulose samples were oxidised using aqueous solutions of H2O2, NaClO or KlO(4), and dissolved in the LiCl-DMAc solvent system using activation with water and a solvent exchange procedure. Viscometry in the cupriethylenediamine (CED) solvent system was performed following the standard technique. Oxidised cellulose samples are prone to degradation by alkalis, While the dissolution in LiCl-DMAc was shown not to have a degrading effect, the oxidised cellulose samples are unstable in the highly alkaline CED solvent, thus introducing a systematic error to the viscometric measurements. A stabilising reduction procedure usually recommended for such samples was tested, and shown to be advantageous, although degradation cannot be completely avoided

Partitioning of Zn, Pb and Cd in river sediments from a lead and zinc mining area using the BCR three-step sequential extraction procedure

The extent of pollution was investigated in sediments collected along the course of the river Meza and its tributaries in the lead and zinc mining area of the Mezica valley (Slovenia). In order to evaluate the heavy metal burden, total concentrations of Zn, Pb and Cd were determined and the partitioning of these metals between the easily and sparingly soluble sediment fractions was performed by the use of the slightly modified BCR sequential extraction procedure. The quality of analytical data was checked with Certified Reference Material CRM 601. Good agreement between the determined and certified or indicative metal concentrations was obtained. In order to estimate the natural and anthropogenic inputs of Zn, Pb and Cd in the sediments, normalisation to Al was applied. The results of the partitioning study indicate that Zn prevails in the most sparingly soluble fraction and is distributed between organic matter and sulfides, while a smaller proportion is found in the easily soluble fraction. Pb is distributed mainly between organic matter and sulfides, whereas Cd is predominantly associated with the most sparingly soluble fraction. Data from the normalisation procedure indicate that the anthropogenic inputs of Zn, Pb and Cd correlate with the very high total metal concentrations determined in sediments. The highest total Zn, Pb and Cd concentrations (16.3. 9.3 and 0.13 g kg(-1), respectively) were found in the sediment of the Helena rivulet, arising from former mining activities. In spite of the relatively low easily soluble metal fractions in the sediment, the concentrations of metals in these fractions are high, owing to the extremely high total metal concentrations. These data indicate severe pollution of the terrestrial and aquatic environment.

Ex situ and In situ Infrared Spectroelectrochemical Investigations of V 2 O 5 Crystalline Films

Vanadium oxide (V 2 O 5 ) films were prepared by dip-coating from V-oxoisopropoxide sols and heating at 300°C for 1 h. Transmission electron microscopy combined with small area electron and X-ray diffraction revealed that the films consist of disordered V 2 O 5 grains with an orthorombic structure (P mmn ). Electromotor force (emf), cyclic voltammetric (CV), and chronocoulometric measurements, combined with in situ ultraviolet-visible (UV-vis) spectroelectrochemical measurements, revealed similar electrochromic and electrochemical properties with other sputtered and sol-gel derived V 2 O 5 films. IR absorbance and reflection-absorption spectra, performed at near-grazing incidence angle (NGIA) conditions (80°, P-polarized), allowed us to compare the observed transverse optical (TO) and longitudinal optical (LO) frequencies of films with the TO and LO mode frequencies obtained from the dispersion analyses of V 2 O 5 crystalline reflection IR spectra. TO and LO spectra of charged films show that Li + …O interactions modify the terminal V-O A (vanadyl), bridging V-O B -V, and edge-sharing V-O C stretching frequencies, suggesting that these interactions take place between the oxygens bordering the cavities in which Li + ions are accommodated during charging. The red-frequency shift of the V-O A stretchings [1016 cm - 1 (TO), 1035 cm -1 (LO)] and the disappearance of the bridging V-O B -V stretching mode [795 cm -1 (TO), 895 cm -1 (LO)] can be used as a diagnostic tool to differentiate between films cycled in the safe and unsafe potential regions. A polaron absorption was observed above 2000 cm -1 in the ex situ TO and in situ NGIA reflection-absorption (LO) spectra of films charged in the safe potential region.

Non-Destructive Evaluation of Historical Paper Based on pH Estimation from VOC Emissions

Volatile organic compounds (VOCs) emitted from materials during degradation can be a valuable source of information. In this work, the emissions of furfural and acetic acid from cellulose were studied using solid-phase micro-extraction (SPME) in combination with gas chromatography-mass spectrometry. Two sampling techniques were employed: static headspace sampling using SPME for 1 h at 40 °C after 18-h sample preparation at 80 °C in a closed glass vial, and contact SPME in a stack of paper (or a book). While a number of VOCs are emitted from paper under conditions of natural or accelerated degradation, two compounds were confirmed to be of particular diagnostic value: acetic acid and furfural. The emissions of furfural are shown to correlate with pH of the cellulosic environment. Since pH is one of the most important parameters regarding durability of this material, the developed method could be used for non-destructive evaluation of historical paper.

Amperometric determination of cyanide by use of a flow-through electrode☆

A new approach to cyanide determination based on the measurement of the diffusion current arising from the oxidation of silver to dicyanoargentate(I) is described. Parameters defining the effect of the electrode geometry and the hydrodynamic characteristics of the system on the response of the electrode have been evaluated so that the performance can be optimized. Response is fast and linear for levels from one microgram to several grams per litre of solution. By use of the flow injection principle and a manifold arrangement, absolute amounts of less than one nanogram of cyanide can be determined precisely in volumes as small as 10 mul and at a rate exceeding 100 samples per hour. The method is easily adapted to automated routine analytical control and continuous monitoring of industrial processes depending on the use of cyanide, such as galvanizing plants and certain organic synthetic industries, and also to control of effluents.