Radiotracer investigation of nickel tetracarbonyl generation and nickel in situ deposition within a graphite furnace

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Abstract
The efficiency of wet chemical generation of nickel tetracarbonyl and the efficiency of electrothermal trapping of nickel from the volatile carbonyl within a longitudinally heated graphite furnace was studied separately by a radioactive indicator technique using the nuclides 56,57Ni. Generation and trapping efficiencies of up to 90 and 95%, respectively, were found. Consequently, an overall efficiency of about 80–90% could be achieved for the carbonyl generation in situ trapping electrothermal atomic absorption spectrometric method used in the determination of ultratrace amounts of nickel. In addition to the acidity of the reaction mixture, the kinetics of the carbonylation plays a very important role in the generation of nickel tetracarbonyl. This phenomenon should be taken into account when designing a carbonyl generator. The interference of “heavy metal" ions, e.g. copper and zinc, seemed to be related to superimposed non-recognized processes taking place in the carbonylation reactor. Compromise conditions should be applied for effective trapping of nickel introduced into the atomizer as the volatile carbonyl. The most important parameters are the temperature of the graphite tube, the total gas flow rate and the position of the introduction capillary. By performing radiographic experiments, nickel was found to be deposited of a small area on the wall opposite the injection hole of the graphite tube. Very good agreement of results (within an uncertainty of 3% RSD) was obtained when evaluating overall efficiency from radioactive and complementary spectrometric data, demonstrating that the spectrometric approach is suitable for evaluating the overall efficiency.