Corrosion process of stainless steel in natural brine as a source of chromium and iron - the need for routine analysis.

The corrosion of the installations carrying high salinity water is particularly important in the case of utility and therapeutic waters, such as natural brine. The analysis of such complex systems is challenging in the context of routine analysis of Fe and Cr. Both elements can be determined by UV-Vis spectrophotometry after only 1 : 100 dilution and liquid-liquid extraction (LODFe = 0.03 mg L-1) or thermal chloride stripping (LODCr = 0.02 mg L-1). The corrosion process was characterized. Electrochemically accelerated corrosion showed uneven decomposition of the steel components - Cr is less easily released to the solution than Fe. Iron comprises 53% of the dissolved part, and Cr comprises 8.6%, while the steel originally contained 62% of Fe and 18% of Cr. During the short-term (one week) contact of the brine with stainless steel, the amounts of Fe and Cr released to the brine were insignificant from the perspective of its therapeutic value.

Simplification of organic matter before voltammetric determination of Tl(I) and Tl(III) in water using nanostructured photocatalyst and solar light.

The crucial point of this study was to verify the hypothesis that both thallium species are not affected by the procedure of photolysis when it is applied as a method of simplification of sample matrix containing surfactants, and that this method of sample pretreatment leads to reliable results of Tl speciation analysis. It is important especially because of high instability of Tl(III), which makes partial reduction of Tl(III)DTPA complex unavoidable. After conservation of Tl speciation by addition of DTPA the photolysis assisted with nanostructured hierarchically organized film was performed using "solar lamp" (Fe2O3/WO3/Fe2O3 film, pH 6, 380-800 nm). The results imply that under proposed photolysis conditions Tl(I) is not oxidized in the presence of water matrix, SDS nor DTPA. Also, even 100-fold excess of Fe(III) ions over Tl(I) ions does not accelerate the oxidation of Tl(I) to Tl(III), and already 2 h of heterogeneous photolysis allow to limit the interferences caused by SDS and obtain reliable results. The data obtained by anodic stripping voltammetry (ASV) were verified using an inter-method comparison with SEC ICP MS. Moreover, after 2 h irradiation the reduction rate of Tl(III)DTPA standard solution increased only slightly from 2-3% to 4-6%. The presence of river water matrix causes a slightly higher (9%) reduction of the trivalent form. These changes are irrelevant in the context of instability of Tl(III) compounds. This study indicates that "soft decomposition" can be applied in speciation analysis of thallium in water matrix.