Thermospray nebulization for flame furnace atomic absorption spectrometry - Correlations between spray formation and cadmium analytical sensitivity

Some parameters which influence thermospray formation at low flow rate used in thermospray flame furnace atomic absorption spectrometry were systematically evaluated using spray morphology (through high-speed images acquisition) and Cd determination (used as an analytical probe). A correlation was observed between Cd sensitivity and the Sauter mean diameter of droplets of the spray introduced into the furnace. The SMD was calculated according to the empiric equation proposed by Elkotb and some physical properties of the carriers were used. Among the parameters studied, the most important is the total area of the inlets of flame gases (bottom holes of the nickel atomizer tube), since Cd sensitivity was drastically reduced when this area was increased. Another important parameter is the chemical nature of the carrier solution, which affects the pulse rate of the thermospray. The average rates measured for the different carriers were 320 ± 50, 290 ± 50 and 60 ± 20 pulses/s for water, 0.9 mmol L-1 Triton X-100 and 44% (w/w) acetonitrile, respectively. Cadmium determinations were performed in certified reference materials using different carrier solutions, and accurate determinations were attained with the use of four carrier liquids (water, 1.4 mol L-1 nitric acid, 0.6 mol L-1 hydrochloric acid, 8% (w/w) ethanol)