Tungsten atomizer-action of modifiers

Tungsten atomizers have been used for electrothermal atomization in atomic absorption spectrometers since 30 years. Various matrices have been analyzed with and without modifiers. Various modifiers have been used, e.g. NH4H2PO4, Pd, Pd and Mg, Al(NO3)3, which are common in graphite furnace too. Action of modifiers with a tungsten surface is different from action on graphite, because the reaction of tungsten with analyte, protective gas (hydrogen) and modifiers causes reduction of analytes. We have studied the interaction of Cd with the tungsten surface, hydrogen and NH4H2PO4 or Pd as nitrate after each step of the heating program. Morphology of newly produced compounds on the tungsten surface was studied by an electron raster microscope and energy dispersive X-ray analysis. The following results and their comparison with theoretical assumptions enables us to suppose, that action of NH4H2PO4 with Cd consists in the formation of less volatile phosphate compounds and action of Pd in the formation of relevant metal, which is covered by Pd in elementary metallic form. Both modifiers shift the pyrolysis temperature to higher values. However, NH4H2PO4 or Pd as nitrate do not realize such shift of temperature as observed when using a graphite furnace.