FURNACE ATOMIZATION PLASMA EMISSION-SPECTROMETRY AT CONTROLLED PRESSURES

A furnace atomization plasma emission source was operated in a control led 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 wel l 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 analyte s and He I. This can be attributed to increases in the gas density and collision frequency. Response reached an optimum slightly above atmos pheric pressure and declined thereafter. At high pressures (> 1200 Tor r), the emission from Cd, Pb and Ag again increased, probably as a res ult of an increase in the efficiency of deposition of these analytes o nto a cooler CE (secondary site). The effect of pressure on detection limit and linear range of calibration for Cd and Mn was also examined.