An evaluation of the parameters which effect the collection efficiency of metals in an aerosol via an improved impaction-graphite furnace atomic absorption spectrometric system showed that an optimum could be obtained at a jet diameter of 1.50 mm, and a jet exit -to-impaction surface distance of 3 mm. Low flow rates gave poor precision at low concentrations except when a large jet diameter was used. Preliminary studies by electron microscopy of particle size collected showed that the higher the flow rate and smaller the jet diameter, leads to a more dense concentration of particle sizes.