Effect of refractory element carbide coating of a pyrolytically coated graphite furnace on injectable sample volume in the electrothermal atomic absorption spectrometric determination of lead

The effect of treating the surface of a pyrolytically coated graphite furnace with various refractory elements, such as Hf, Nb, W and Zr, on the injectable sample volume was evaluated in order to enhance the sensitivity. Treatment with W made it possible to introduce a 100 mu l aliquot of sample solution into the furnace with a high precision (RSD < 3%) for up to 250 firings. A good linearity (correlation coefficient > 0.99) between integrated absorbance and injection volume was observed in the range 0-100 mu l. Use of a Pd modifier made it possible to enhance the precision (RSD < 2%) and the stability of the integrated absorbance (RSD < 2.5%) for up to 250 firings. A good linearity was also observed. The calculated detection limit and characteristic mass (sensitivity) were 0.02 mu g l(-1) and 12 pg, respectively, for a 100 mu l injection with the Pd modifier at the optimum ashing temperature of 1400 degrees C. An interference study was also carried out. The recoveries of 2 mu g l(-1) Pb added to various water samples, such as snow, rain, river water and tap water were 96-106%.