Analysis of metal and semimetal trace constituents

The determination of metal and semimetal trace constituents in different materials requires extra measures to prevent contamination and analyte losses and presupposes top-performance analytical instruments with powerful detection capabilities. Solid samples and samples that are not clear are decomposed in a microwave oven. The acid mix used for decomposition is often made up of a mixture of concentrated nitric acid and hydrofluoric acid. The solutions obtained are evaporated until they are almost completely dried. Each sample is decomposed at least twice, and different methods of trace element analysis are applied to identify the various elements it contains. The analysis method has to be chosen individually for each element.

Flow injection cold vapour atomic absorption spectrometry (FI-CV-AAS) is employed to determine the element mercury. The decomposition solution prepared for analysis and the calibration solutions are stabilised with potassium permanganate. The sample solution is pumped into the reaction chambers of the analyser by means of a flow injection system and mixed with the reducing agent tin(II) chloride there. In this way, mercury compounds are reduced to form elemental mercury, which an argon flow carries along to the UV measuring cell. This is where the mercury concentration is determined by measuring the absorption of UV radiation by the mercury atoms.

Arsenic analysis is conducted by means of graphite furnace AAS (GF-AAS) first. In case of doubt flow injection furnace hydride generation (FIFU-HG-AAS) is applied. FIFU-HG-AAS has the advantage that only elements which form volatile hydrides enter the graphite tube. In this way, numerous interferences caused by other constituents of the sample can be excluded.

The above elements are analysed by means of ICP mass spectrometry. As interferences resulting in incorrect analysis results may occur with this analysis method as well, the elements cobalt, copper, nickel, lead, antimony, thallium and vanadium in particular are analysed by GF-AAS for comparison.