Behaviour of chromium in the graphite furnace during the performance of the flameless absorption spectrometry

Summary

By means of⁵¹Cr as radiotracer, the behaviour of chromium in the graphite tube during the individual steps of the temperature program was investigated. The investigated matrix systems include 1 mol/l HCl, 0.2 mol/l HNO₃, 0.2 mol/l NaCl, human serum and urine, cow milk, a tetramethylammonium hydroxide solution of hair, a solution of Cr-diethyldithiocarbamate in MIBK, and a HF/ HNO₃/H₂O₂ solution of niobium. Excluding the last two matrices, the labelling was carried out with both the⁵¹Cr³⁺ and⁵¹CrO ²₄ -. Without matrix modification, a charring temperature between 1200 °C and 1400 °C can be used for the investigated samples. No significant difference was observed between uncoated and pyrolytically coated tubes. Significant stabilization effects can be achieved in the pre-atomization step by using tungsten-coated tubes and/or matrix modifiers of which Na₂WO₄, Na₂MoO₄ and H₂O₂ proved to be well suited. Optimum experimental conditions were found for the execution of the atomization step. The results obtained in some special experiments indicate that no strong retention of chromium on the surface of the graphite tube by carbide formation is taking place.