Abstract
The method for the determination of total mercury levels in organic materials by means of combustion and use of gold trap has been improved. Mercury in organic materials can be analyzed by both oxygen combustion method and air combustion method. In the oxygen combustion method, samples are burned in the stream of oxygen followed by complete combustion in the high temperature zone heated in the range from 800 to 900°C (Fig. 1). In the air combustion method, combustion is completed at 850°C in the combustion tube which is packed with copper oxide wire through which air flows as shown in Fig. 2. In both methods, oxides of nitrogen and oxides of sulfur formed during the combustion are removed by absorbing them into the layer of alkali metal carbonate. Mercury vapor generated by the combustion is led to the gold trap where mercury is trapped forming amalgam. On heating the gold trap, mercury vapor is released and determined by a mercury vapor analyzer.
The gold trap is prepared by impregnating HAuCl4 into porous support, followed by thermal decomposition of HAuCl4 forming thin layer of gold on the surface of the support. Results of repeated test for trap and release of mercury by this gold trap show good reproducibility. Within the scope of this study, no oxidation of mercury during the combustion is observed. Capability of present methods are demonstrated by analyzing for mercury in fish or other biological materials, and good agreement of results with wet digestion method is obtained. The optimal sample amount in oxygen combustion method and air combustion method are 100300 mg and 100200mg of fresh fish, 1040 mg and 1030 mg of hairs, about 500 mg and 300 mg of white of egg, and about 200 mg and 150 mg of cereals respectively. However, upper limit of sample amount in the oxygen combustion method can be increased by increasing the flow rate of oxygen. In case of samples containing mineral acids or relatively large amounts of sulfur compounds, acidic gases which flow past the alkali carbonate layer condense at the inside wall of the condenser causing interference in the measurement of mercury. This interference is removed by heating the sample covered with thin film of lime. The time required for combustion and measurement is within about 5 minutes.
