Inorganic arsenic speciation by differential pulse anodic stripping voltammetry using thoria nanoparticles-carbon paste electrodes.

Two novel thoria (ThO2) nanoparticles-carbon paste electrodes were used to evaluate an anodic stripping voltammetric method for the direct determination of arsenite and total inorganic arsenic (arsenite plus arsenate) in water samples. The effect of Ag((I)), Cu((II)), Hg((II)), Sb((III)) and Se((IV)) ions on the electrochemical response of arsenic was assayed. The developed electroanalytical method offers a rapid procedure with improved analytical characteristics including good repeatability (3.4%) at low As((III)) concentrations, high selectivity, lower detection limit (0.1 µg L(-1)) and high sensitivity (0.54 µA µg(-1) L). The analytical capability of the optimized method was demonstrated by the determination of arsenic in certified reference materials (trace elements in natural water, trace elements in water and coal fly ash).

Modelling of chemical fractionation patterns of metals in soils by two-way and three-way principal component analysis.

The 'pseudo-total' contents and the chemical fractionation pattern of eight toxic elements (As, Cd, Co, Cu, Cr, Ni, Pb and Zn) have been determined in 12 soil samples collected around a coal-fuelled power plant (Velilla del Río Carrión, Spain) by using, respectively, the US-EPA 3051 norm and the modified BCR (SM&T) chemical fractionation procedure. The 'pseudo-total' dataset has been analyzed by classical two-way principal component analysis (PCA) finding a PC accounting for the metal 'pollution' of the area. On the other hand, the three-dimensional (samples x metals x fractions) X array obtained after application of the modified BCR SM&T procedure, has been studied by matrix augmentation (MA-PCA) and three-way principal component analysis (3-PCA) using PARAFAC and TUCKER3 models. Whereas both MA-PCA and PARAFAC originated two-factor models biased towards the different chemical fractionation of the samples, the best TUCKER3 model [1, 2, 2] takes into account simultaneously both the 'pseudo-total' contents and the chemical fractionation of the soil samples. Therefore, the TUCKER3 originated a better representation of the global environmental impact caused by the power plant, and the plotting of the soil samples loadings, A1, in the physical space allowed to locate the most potentially hazardous areas.

Natural radiation doses to the population in a granitic region in Spain.

The global average effective dose from natural radiation sources is estimated to be 2.4 mSv y(-1). Nevertheless, local variations in the radiation exposure may differ by orders of magnitude. In this paper, we study a rural area in western Salamanca (Spain) where doses are potentially well above the stated average value. Its geology consists mostly of granite and schist, presenting various uranium mineralisations, some of which were exploited in former years. Water samples, both surface and groundwater, were collected in selected villages and measured by liquid-scintillation spectrometry. 222Rn in dwellings was determined in dwellings by means of short-term measurements, using Picorad vials and long-term measurements with CR-39 detectors. The committed effective doses to the inhabitants due to indoor 222Rn and 222Rn and 226Ra in drinking water were assessed using the dose conversion factors proposed in the UNSCEAR 2000 report.

Determination of copper and arsenic in refined beet sugar by stripping voltammetry without sample pretreatment.

Copper and arsenic have been analysed in refined beet sugar at the microgram kg-1 level by anodic stripping voltammetry (copper) and cathodic stripping voltammetry (arsenic) in the differential-pulse mode (DPASV and DPCSV) at a hanging mercury drop electrode (HMDE). DPCSV measurements of arsenic are based on its accumulation onto the HMDE as an intermetallic Cu-As compound followed by the reduction of As0 to arsine in hydrochloric acid medium. Measurements were directly carried out on untreated sugar solutions. The performance of the procedures was compared with electrothermal atomic absorption spectrometry and stripping voltammetry applied to digested sugar samples, and showed in general better accuracy. The procedures were applied to the determination of these toxic elements in commercial beet sugar samples of concentrations below 50 micrograms kg-1 copper and 15 micrograms kg-1 arsenic were found, which are much lower that those allowed by the current regulations.

Modification of the methylene blue method for spectrophotometric selenium determination.

The spectrophotometric method for Se(IV) determination based on its catalytic effect in the reduction of Methylene Blue (MB) by sulphide is modified. The variables that affect the decolorization of MB were taken into account: reagent concentrations, order of addition, mixing and standing times, pH, ionic strength, temperature, solution volume, wavelength, etc. The results of this study allowed a decrease of the determination limit and, by selection of the appropriate analytical conditions, choice of optimum linear range according to the selenium content in the sample. The lower limit range is 15-75 mug/1., with 3% relative standard deviation and no systematic errors. Procedures for overcoming several potential interferences were studied. The proposed method was applied to several environmental samples and the results were compared with those obtained by other standard methods.

Total and extractable contents of trace metals in agricultural soils of the Valderas area, Spain.

The surface horizons of four agricultural field soils (Mollic ustifluvents, Alfic Xerochrepts, Typic Palexeralfs, Typic Haploxeralfs) were sampled to determine the total copper, cobalt, molybdenum, zinc, chromium, nickel, selenium, cadmium, lead, mercury, lithium and strontium, and were also fractionated by an extraction procedure to estimate the quantities of these trace metals in soluble form. The extractants used were the following: 1.0 N NH4 OAc for lithium and strontium, 0.05 M Na2-EDTA for cadmium, copper, nickel and zinc, 2.5% (w/v) acetic acid for lead, 2.5% (w/v) acetic acid and 2% (w/v) dithizone for cobalt, 2% (w/v) diethyldithiocarbamate solution for selenium, 0.1 NHCl for chromium, and 0.5 NHCl for mercury. The total content of these twelve elements in the four field soils sampled were lower than the levels quoted in the literature, although for different geochemical systems. The percentage of the total element content in soluble form was (except for selenium) generally very low, averaging between 5.5 and 8% for copper, 1.6 and 2.5% for cobalt, 8 and 10% for molybdenum, 1.8 and 2.2% for zinc, 14.2 and 17.7% for chromium, 5.5 and 6.4% for nickel, 30 and 55% for selenium, 8 and 14% for cadmium, 3 and 3.6% for lead, 8.3 and 11% for mercury, 5 and 7% for lithium, and 4.4 and 5.7% for strontium, regardless of the soil type.

Determination of indium in aluminium alloys by flame atomic-absorption spectroscopy and flame atomic-emission spectrometry.

The use of flame atomic-absorption and atomic-emission spectrometry for the determination of indium in aluminium alloys is described. Two types of flame are used: air-acetylene and nitrous oxide-acetylene. The efrect of other ions, especially aluminium, has been studied, and the use of lanthanum as a releasing agent is proposed for both techniques, the amount used depending on the amount of aluminium present.

An indirect method for determining phosphorus in aluminium alloys by atomic-absorption spectrometry.

An indirect method is described for the determination of phosphorus in aluminium alloys. Ammonium molybdate is added to a solution of the aluminium alloy and the molybdophosphoric acid formed is selectively extracted into n-butyl acetate. The twelve molybdenum atoms associated with each phosphate ion are determined by direct atomic-absorption spectrometry with the n-butyl acetate phase in a nitrous oxide-acetylene flame, with measurement at 313.2 nm. The most suitable conditions have been established and the effect of other ions has been studied.