Effect of anode dimensions and location of the discharge gas inlet port on the spatial distribution of copper atoms in a radio frequency glow discharge atomizer for atomic absorption spectrometry

The absorbance of Cu atoms sputtered from a Cu cathode in a laboratory-modified radio frequency glow discharge atomizer for atomic absorption spectrometry was measured at different regions within the atomizer chamber for different discharge parameters. The results show that not only the discharge gas flow rate and pressure but also the applied rf power and the degree of extension of the negative glow have significant effects on the atomization and on the distribution of sputtered atoms within the atomizer chamber. The influence of various diameters and thicknesses of the sampling orifice (anode) on the plasma atomization characteristics and the sample weight loss rates has been examined. By increasing the diameter of the sampling orifice, a larger area of the cathode surface (Cu) was allowed to be sputtered, thereby generating a larger number of atoms (higher absorbance) in the analysis volume, where the sputtered atoms were studied by atomic absorption spectrometry. The absorbance of Cu atoms was inversely related to the thickness of the sampling orifice disk because the distance of the investigated region of the atomizer chamber from the cathode surface increases with increasing thickness of the sampling orifice disk. The rate of sample weight loss was inversely related to the diameter of the sampling orifice at orifice diameters higher than or equal to 4 mm. The rate of sample weight loss as a function of the thickness of the sampling orifice disk indicated that the transport efficiency of the sputtered atoms into the atomizer chamber was higher when a sampling disk having a thickness of 2 mm was used. Changing the location of the discharge gas inlet port resulted in a large increase in the atomic absorption signal. A larger increase in the atomic absorption signal of the sputtered Cu atoms was observed for the modified rf atomizer having the discharge gas inlet port on the body of the sampling orifice disk than for the unmodified rf atomizer having the discharge gas inlet port on the top of the atomizer chamber.