The preparation and characterisation of a laboratory quality control material (QCM) for dibutyltin (DBT) and tributyltin (TBT) in sewage sludge is reported. The reference values were determined by the use of two different types of isotope-dilution mass spectrometry: gas chromatography–mass spectrometry (GC-MS) and gas chromatography–inductively coupled plasma mass spectrometry (GC-ICP-MS). Different extraction methods were tested (microwave- and ultrasound-assisted extraction and mechanical stirring). The reference values obtained were 1553±87 and 534±38 ng Sn g-1 for DBT and TBT, respectively. The QCM will be used for study of the inhibition of the nitrification by OTC in activated sewage sludge.
COBISS.SI-ID: 25672231
The use of high matrix interface that removes high salt concentrations and introduction of helium into collision cell enables Effective reduction of polyatomic interferences produced by high chloride and carbon concentrations in determination of Cr(VI) by FPLC-ICP-MS. The developed procedure for effective removal polyatomic interferences in determination of hexavalent chromium enables investigations of oxidation-reduction processes in environmental samples in wide pH range and the use of stable Cr isotopes as tracers.
COBISS.SI-ID: 25376807
New procedure for preparation of enriched isotopic solutions of 50Cr(VI) and 53Cr(III) was developed. 50Cr(VI) was prepared from 50Cr enriched oxide by alkaline melting with KNaCO3 and the use of Bunsen burner. High temperature and high pH enabled quantitative oxidation of Cr(III) to Cr(VI). The melt was then dissolved with HCl. Moreover, the microwave assisted digestion procedure of 53Cr enriched oxide was applied for preparation of 53Cr(III) spike solution by microwave assisted digestion with HNO3 and stabilization of sample by HCl. By the procedure developed the isotopic solutions were prepared without use of oxidizing and/or reducing agents. The outcomes of our investigation highlighted the importance of the adequate preparation of spike solutions of Cr isotopes that may be used as reliable tracers in the investigations of the oxidation-reduction processes of Cr in wide range of environmentally relevant pH values.
COBISS.SI-ID: 25807399
Chromium (Cr) conversion coatings are used as decorative finishes and to improve the corrosion protection and strengthen the wear resistance of metallic surfaces. Cr electroplating frequently involves the use of Cr(VI). To reduce environmental impacts, several EU directives restricted its use to threshold values of 0.1 % Cr(VI) by weight per homogenous material in vehicles, and 1000 mg kg-1 of Cr(VI) in electronic and electrical equipment. There are only few analytical procedures reported that comply with legislative demands. In our work a selective, quantitative and sensitive analytical procedure for determination of Cr(VI) in the corrosion protection coatings was developed. The investigation was performed on metallic plates homogenously treated by chromium conversion or hard chrome coatings on copper or zinc electroplated steel surfaces. An alkaline solution (pH 12) was used for ultrasonic extraction of Cr(VI). Speciation analysis was performed by anion-exchange HPLC-ICP-MS. Species interconversions during the analytical procedure were followed using enriched isotopic solutions of 50Cr(VI) and 53Cr(III). To prevent Cr(III) oxidation, TRIS, EDTA or MgCl2 were added along with a double isotopically enriched spike and extractions performed over different time periods. Under optimal conditions that prevent any species interconversion (30 min ultrasonic extraction at 70 °C using 2 % NaOH + 3 % Na2CO3 + MgCl2 as extraction agent), six consecutive extractions were necessary to quantitatively extract Cr(VI) from the protective layers, while its content was determined by speciated isotope dilution ICP-MS.
COBISS.SI-ID: 25911847
Recently several papers were published in highly ranked journals on the presence of Cr(VI) in tea infusions and bread samples. These statements were made on the basis of determination of total Cr concentrations in alkaline and aqueous sample extracts, without applying any speciation analysis. If Cr(VI) really exists in bread samples and tea infusions, consumption of bread and tea would represent long-term chronic exposure to Cr(VI) and a health threat for the majority of the human population. It is well accepted that due to the presence of organic matter foodstuffs of plant and animal origin cannot contain Cr(VI). To show that the reported data on the presence of Cr(VI) in foodstuffs are an artefact of inappropriately applied analytical methodology, investigation of speciation was carried out by high performance liquid chromatography – inductively coupled plasma mass spectrometry (HPLC-ICP-MS). 50Cr(VI) and 53Cr(III) stable isotopes were used to follow species interconversions during the extraction procedures. Separated Cr species eluted from the column were followed at m/z 50, 52 and 53. The speciation analysis data demonstrated that in all samples analysed Cr(VI) concentrations were below the limit of detection. In tea infusions 50Cr(VI) was almost completely reduced due to the presence of antioxidants, while the high content of organic matter in bread appreciably reduced 50Cr(VI) even in highly alkaline (pH 12) bread extracts. Our investigation confirmed that Cr(VI) does not exist in foodstuffs of plant origin.
COBISS.SI-ID: 26528039