The anti- and prooxidative properties of gallic acid in Fenton-type systems containing H(2)O(2) and Fe(III) were examined in pH 3-10 reaction media and at reaction temperatures of 20-50 degrees C. Although it is a free radical scavenger, gallic acid may exhibit prooxidative properties, as it promotes the production of hydroxyl radicals due to iron chelation. The overall effect is prooxidative if the ratio of the concentrations of gallic acid and Fe(III) in the reaction medium is smaller than 2. If the ratio is greater than 2, the overall effect of gallic acid presence is antioxidative due to free radical scavenging properties. The dependence of rates and of apparent activation energies of gallic acid consumption on pH in Fenton-type systems was also examined, and it is concluded that the rate-determining steps in acidic and alkaline media are different, the overall rate of gallic acid consumption being lowest at pH 7.

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The composition of the passive layers formed by electrochemical oxidation at different passivation potentials on Co-Cr-Mo and Co-Ni-Cr-Mo alloys in simulated physiological solution (SPS), with and without the complexing agent EDTA, was studied by X-ray photoelectron spectroscopy. Composition as a function of depth, cationic fraction and thickness of the passive film was determined. Chromium oxide is shown to be the major constituent of the passive layer on both Co-Cr-Mo and Co-Ni-Cr-Mo alloys. The minor constituents of the passive layers, Co- and Mo-oxide in the case of Co-Cr-Mo alloy and Ni-, Co- and Mo-oxides in the case of Co-Ni-Cr-Mo alloy, are also located in the outer part of the layer. EDTA affects the formation of the passive layer on each alloy. The content of Co-, Ni- and Mo-oxide in the passive layer is lower in the presence of EDTA, thus indicating increased solubility associated with higher stability constants for complexes of metal cations with EDTA.

A study is presented on the characterization, evaluation and optimization of several key operational parameters for a reliable and effective use of a bismuth film electrode (BiFE) as an advanced replacement of the mercury film electrode in anodic stripping voltammetric measurements of trace heavy metals. Applying in situ preparation of the BiFE and employing lead(II) and cadmium(II) as model analyte ions, key parameters including bismuth precursor salt and substrate surface (platinum, gold, glassy carbon, carbon paste, carbon fiber) for bismuth plating, concentration as well as cationic and anionic composition of the measurement solution, solution pH and temperature, potential interferents, and stripping modes were carefully examined for their effects in the preconcentration and stripping steps. Parameters such as substrate surface (except platinum), precursor salt, solution matrix and temperature showed no or little impact on the BiFE performance in stripping analysis. On the other hand, the BiFE performance was found to be dependent on the solution pH (with maximum efficiency in the range of 4 to 5), on the stripping mode (with squarewave voltammetry as the best choice) and to a certain degree on the presence of surface active substances. The results revealed that the non-toxic solid-state BiFE is applicable under a wide variety of conditions which proves it highly suitable for practical work in environmental trace heavy metal analysis.

This article reports on the novel mixed cobalt and copper hexacyanoferrate (CoCuHCF)-modi®ed carbon ®ber cylinder microelectrode (CFCME) and its application to potentiometric determination of highly toxic hydrazine. The substrate CFCMEs were fabricated in a standard manner using carbon ®bers of 7 mm in diameter. The CoCuHCF ®lm 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 ®lm in the presence of hydrazine, with the potential (emf ) slope of 7 55 mV/decade, was compared with those of four single metal HCF ®lms (CoHCF, CuHCF, FeHCF, and NiHCF) prepared in the same way, and the possible role of the CoCuHCF ®lm components is explored and discussed. The emf versus log C Hyd calibration plot was linear over 3 orders of magnitude, from 1.0610 76 to 1.0610 73 mol/L, with a correlation coef®cient of 0.995. The limit of detection was found to be 5610 77 mol/L. The response times of 10 to 30 s and the temperature coef®cients 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 Na®on coating. The useful lifetime of the all-solid microsensor was found to be more than 2 months when stored in air.

Sampling restrictions in analysis of cultural heritage materials narrow the choice of appropriate analytical methods considerably. In this work, near- and mid-FT-IR reflectance data were related to paper properties determined with classical analytical methods using partial least-squares. Nondestructive determination of properties, which are of importance for evaluation of the long-term stability of historical paper, i.e., ash content, lignin content, degree of polymerization of cellulose, pH, and aluminum content, is possible. With the use of a considerable sample set, satisfactory reliability was achieved for all properties but aluminum content. Considering that with age, chemical properties of paper change, dating of historical documents was attempted for the first time, also with success.

Speciation of low molecular weight (LMW) Al complexes was performed in human serum from eight healthy volunteers in order to investigate the individual variability in the percentage and composition of LMW-Al species. Spiked samples (100±120 ng cm 23 Al 3z ) were microultra®ltered through a membrane ®lter (cut-off 30 000 Da) to separate Al bound to transferrin from LMW-Al complexes. A 0.5 cm 3 volume of the ®ltrate was injected onto an anion-exchange fast protein liquid chromatography (FPLC) column and aqueous 4 mol dm 23 NH 4 NO 3 linear gradient elution was applied for 10 min to separate LMW-Al complexes. Fractions of 0.2 cm 3 were collected throughout the chromatographic run and Al was determined `off-line' by electrothermal atomic absorption spectrometry (ETAAS). The characterisation of LMW-Al species in spiked serum was performed not only on the basis of the retention time (ETAAS detection), but also by electrospray (ES)-MS-MS analysis. A tandem quadrupole mass spectrometer equipped with a Z spray ion source as LC-MS interface was used for the identi®cation of LMW ligands eluted under the chromatographic peaks. It was found experimentally that the amount of LMW-Al species in spiked serum ranged from 14 to 55%. On the basis of FPLC-ETAAS and ES-MS-MS analysis, it was found that the main LMW-Al species present in serum were Al-citrate, Alphosphate and ternary Al-citrate-phosphate complexes. The distribution of these species varied among particular individuals. In some of them Al-citrate and Al-phosphate were the main LMW-Al species in serum, while in others the ternary Al-citrate-phosphate complex was also present. The serum of some other individuals did not contain Al-phosphate and the main LMW-Al species were either Al-citrate and Al-citrate-phosphate complexes or Al-citrate species alone. The limit of detection for the separated Al species on the FPLC column was 5.0 ng cm 23 , while the RSD was found to be 8%.

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