Determination of lead in seawater by electrothermal atomic absorption spectrometry with transversely heated furnace by using oxalic acid or Pd/Mg as modifiers

The simultaneous volatilization of seawater salts and lead free atoms induces chemical interferences. Moreover, an under-compensation related to the vaporization of seawater salts is observed; the systematic error depends on the magnitude of the background absorption signal to be corrected and can be very important at low Pb concentrations. In the presence of oxalic acid, which modifies the seawater matrix and promotes a lower atomization temperature, the chemical interference is suppressed and the background absorption signal is dramatically reduced. In the presence of the Pd/Mg modifier and nitric acid, Ph is stabilized at a higher temperature and the major part of the seawater matrix can be removed before atomization, but the integrated absorbance remains depressed. The detection limits obtained for 10 mu l of seawater in the presence of oxalic acid or Pd/Mg and nitric acid used as modifiers are respectively 0.3 mu g l(-1) and 0.5 mu g l(-1).