Abstract
The interference of chloride with the determination of lead by flameless atomic absorption spectrometry was studied when the tube was made by graphite, molybdenum and tantalum. The tubes used were as follows. Graphite tube : diameter 8.0 mm, inside diameter 6.0 mm, and length 32 mm, supplied by Nippon Carbon Corp. (type EG-36 H). Molybdenum tube: purity 99.99 %, diameter 6.8 mm, inside diameter 6.0 mm, and length 32 mm. Tantalum tube : purity 99.99 %, diameter 7.0 mm, inside diameter 6.0 mm, and length 32 mm. The interference was smaller when tantalum tube was used than when graphite tube was used. In order to study the reason for this interference, the liberated gas from the heated tube was analysed by mass spectrometry as follows. Argon gas was supplied at a flow rate of 1.2 1/min, a 10 μl portion of a lead solution was injected into the atomizer and then the tube was heated (the temperature range of 5002400°C). The exhausting gas was collected in a cell and supplied to the mass spectrometer. It was found from the analysis that hydrogen was detected prominently when the tantalum tube was heated above 550°C and when the graphite tube above 1000°C. The atomization of lead was carried out at 2000°C and at this temperature, the amount of hydrogen from the former tube is fifteen times as much as that from the latter. This effect of hydrogen was further studied by supplying argon containing 10 % of hydrogen and a decrease of the interference by chloride was always found with the graphite, molybdenum and tantalum tubes. From these results, the smaller interference by the chloride in the tantalum tube than in the graphite tube was estimated to be due to the reducing action of the hydrogen in the atmosphere.
