Selenium and mercury concentrations in some fish species of the Madeira River, Amazon Basin, Brazil.

Samples of 7 species of piscivorous, omnivorous, and herbivorous fish caught at 12 different sites on the Madeira River, Amazon Basin, were analyzed for selenium and mercury. Selenium was determined by anodic stripping voltammetry and mercury by cold vapor atomic absorption spectrophotometry. The means for selenium concentrations ranged from 0.49 to 3.11 nmol/g and for mercury from 0.41 to 6.66 nmol/g depending on the fish species. The molar ratios of Hg:Se increased according to the fish trophic level. Piscivorous species had the highest mean ratio (4.0) and herbivorous species the lowest (0.9). There was a positive and statistically significant correlation between selenium and mercury concentrations for the herbivorous species (r = 0.716; p = 0.0088) not seen for omnivororus and piscivorous species (r = -0.2032; p = 0.3407). These findings are significant for the fish-eating population of the Madeira River because the ingestion of mercury would always be in excess of selenium.

Multivessel system for cold-vapor mercury generation. Determination of mercury in hair and fish.

A multivessel system for the determination of mercury (Hg) by cold-vapor atomic absorption spectrometry (CV-AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) was developed. The performance of the proposed device was tested by determining total Hg in quality-control samples of hair and fishes following acid digestion. Application of the apparatus to the determination of Hg by CV-AAS following alkaline digestion was studied as well. The detection limit obtained for CV-AAS was 0.11 ng/mL and for ICP-AES 1.39 ng/mL. The results show that the system is appropriate to be used in techniques involving cold-vapor generation of Hg.

Evaluating materials used for constructing soft earmoulds.

The use of penetrometry for the assessment of materials employed for soft earmoulds is investigated. Selected test conditions are used for the characterisation of 10 materials of five types (cold-cured methacrylate, heat-cured methacrylate, heat-cured silicone, polyvinyl chloride co-polymer and polyethylene copolymer) used in clinical practice. The results are compared with the outcome of subjective assessments surveyed for four representative materials. The effect of ageing is assessed for a heat-cured silicone (Molloplast B) and a heat-cured methacrylate (Coe Super-Soft).

Determination of gallium by square-wave voltammetry anodic stripping, based on the electrocatalytic action of 2,2'-bipyridine in dimethylsulphoxide: comparison with an aqueous NaSCN/NaClO(4) electrolyte.

Deposition potential, deposition time, square-wave frequency, 2,2'-bipyridine concentration, and gallium concentration have been studied in detail, for the determination of trace concentration levels of the metal by square-wave voltammetry anodic stripping analysis, in dimethylsulphoxide. Optimum conditions have been found for gallium(III) determination and results compared to those obtained in 0.5M NaSCN + 4.2M NaClO(4) aqueous electrolyte by obtaining calibration graphs for the range 1 x 10(-8)M-1 x 10(-5)M gallium. Accuracy (+/- 3%) and precision (4-6% SD) of this method were assessed with both 4 x 10(-8)M and 4 x 10(-7)M gallium solutions used as synthetic samples. The efficiency of solvent extraction of gallium with di-isopropyl ether was found to be 99.98% at a 4 x 10(-7)M gallium concentration. The proposed method was applied to the determination of the gallium content in rock mineral samples (using the above mentioned solvent extraction procedure), are compared to those obtained with the NaSCNNaClO(4) based electrolyte. No statistically significant difference was observed. Analytical procedures followed are given in detail.

Electrochemical reduction of gallium(III) in non-aqueous solvents, assisted by 2,2'-bipyridine.

The electrochemistry of gallium(III) perchlorate in dimethylsulfoxide (DMSO) and acetonitrile (MeCN) at a mercury drop electrode is described and compared to that in water. The reduction of 2,2'-bipyridine (DIPY) and its interaction with free protons in the solvents mentioned is also surveyed. The electrochemistry of tris-(2,2'-bipyridine) gallium(III) perchlorate was studied in DMSO and MeCN. A gallium metal deposit is obtained by reduction of the complex compound in the first solvent, whereas lower valence gallium-DIPY species are obtained in the second. The existence of different catalytic prepeaks in DMSO is described. The first catalytic peak, which renders a metal deposit, is studied in detail, together with the possible interference of oxygen and free protons. These studies serve the basis of future development of an analytical procedure for the determination of trace concentrations of gallium.