The nature and source of the background absorption of the urine sample and the method of eliminating the background were studied. The wavelength-dependence of urine background is quite similar to that obtained from sodium chloride. This shows that the background absorption of the urine sample arises mainly from sodium chloride. When the general heating mode is used, the outline of the background absorption curves and peak height are dependent on the atomization temperature However, the above dependence is not observed in the case of the max. power heating mode. The background interferences from urine can be decreased by the addition of nitric acid. The choice of appropriate signal recording time, ashing temperature and time, and heating mode are also effective for this purpose.

Key words: ATOMIC ABSORPTION SPECTROPHOTOMETRY, URINE, SODIUM CHLORIDE, GRAPHITIZING FURNACES, AMMONIUM CHLORIDE, HOST IMPROVING AGENTS, ATOMIZATION TEMPERATURE, BACKGROUND ABSORPTION