FURNACE ATOMIZATION PLASMA EMISSION-SPECTROMETRY AT CONTROLLED PRESSURES

A furnace atomization plasma emission source was operated in a controlled pressure He environment (200-2000 Torr) (1 Torr = 133.322 Pa). The response from several elements (Cd, Pb, Ag, Mn, Cu, Fe and Co) as well as emission from He I at 388.8 nm and the temperature of the centre electrode (CE) were measured. Below 800 Torr the temperature of the CE increases with increasing pressure, as does emission from the analytes and He I. This can be attributed to increases in the gas density and collision frequency. Response reached an optimum slightly above atmospheric pressure and declined thereafter. At high pressures (> 1200 Torr), the emission from Cd, Pb and Ag again increased, probably as a result of an increase in the efficiency of deposition of these analytes onto a cooler CE (secondary site). The effect of pressure on detection limit and linear range of calibration for Cd and Mn was also examined.