PARTICLE-SIZE DISTRIBUTION OF SAMPLE TRANSPORTED FROM AN ELECTROTHERMAL VAPORIZER TO AN INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETER

The particles exiting the graphite furnace electrothermal vaporizer (ETV) cell of a commercial ETV inductively coupled plasma mass spectrometer (ICP-MS) were size characterized. It was found that there were a large number of particles leaving a furnace heated with no sample. Assuming all the particles were graphitic, approximately 0.1 mug of material exited the ETV. A common analyte carrier, NaCl, was also characterized and exhibited a bimodal size distribution with a consistent absence of particles in the 0.2-0.3 mum region, which may be explained by the presence of two mechanisms responsible for NaCl particle formation. The mass spectral signals of Na+ and C+ indicated the NaCl and carbon particles were temporally separated. Several parameters were varied (i.e. heating rates, gas flows, transport tube geometries) and their impact on the size distribution was noted. ETV heating rates for 440 and 2000 K s-1 and Ar flows of 1.0 and 1.8 l min-1 produced a statistically insignificant change in the number of particles or their size distribution, except for the 0.3-0.5 mum regime with the varying heating rates. Varying transport tube lengths from 0.2-2.0 m showed subtle effects that were notable for large particles and long tubes.