Hana Dočekalová

Application of diffusive gradient in thin films technique (DGT) to measurement of mercury in aquatic systems

The diffusive gradient in thin films (DGT) technique was investigated and used to measure mercury concentration in river water. Mercury ions are covalently bound to amide nitrogen groups of commonly used polyacrylamide, which makes this gel unsuitable as a diffusive medium. In contrast, agarose gel was found as the diffusive gel for mercury measurements. Basic performance tests of agarose DGT verified the applicability of Ficks first law for DGT measurements. Two selective resins, Chelex-100 with iminodiacetic groups and Spheron-Thiol with thiol groups were used. The measured diffusion coefficient in agarose gel was close to that in water. The concentration of mercury in Svitava river measured by DGT with Speron-Thiol resin gel was higher (0.0116 +/- 0.0009mugl(-1)) than those obtained by Chelex-100 (0.0042 +/- 0.0005mugl(-1)). Different capture efficiencies of two adsorbents enable to estimate fractions of mercury bonded in different complexes in the river water. The concentrations of mercury found by DGT both Chelex-100 and Speron-Thiol resin gels are much lower than that measured directly in the river water (0.088 +/- 0.012mugl(-1)). This difference indicates that DGT concerns inorganic ions and labile species only, and that it is not able to include inert organic species and colloids.

Determination of selenium by electrothermal atomic absorption spectrometry. Part 1. Chemical modifiers

The effect of various chemical modifiers, including nitrates of palladium, nickel, magnesium, calcium, lanthanum, europium and aluminium, on the analytical signal of selenium in a graphite furnace was studied. The signals of various selenium compounds, such as selenite, selenate and organic compounds representing different types of selenium forms in body fluids (selenomethionine and trimethylselenium iodide), were evaluated. The shape of the transient signal appears to be influenced not only by the chemical reactions in the graphite–selenium–modifier system, but also very strongly by vaporization effects connected with the physical character of the charred residue. It follows that successful chemical modification involves the application of a considerable excess (higher than 1000-fold) of some metal nitrates, which produce refractory oxides and no thermally stable carbides, and are at the same time capable of quantitative conversion of the analyte into a single form. An integral part of the modifier action is trapping of the resulting compound by the modifier residue.