Matrix effect on internal standardization in inductively coupled plasma-optical emission spectrometry

The effect of the matrix on internal standardization in inductively coupled plasma-optical emission spectrometry has been studied. Solutions containing cobalt, iron and nickel as analytical elements ; rhodium and yttrium as internal-standard elements ; and sodium, potassium and sulfuric acid as co-existing elements were prepared. The atomic emission intensities of cobalt, iron, nickel, rhodium and yttrium were observed in both the axial and the radial observation modes. When sodium was co-existing, the intensities of the atomic lines of analytical and internal elements were decreased with increasing sodium concentration in the axial observation mode. On the other hand, in the radial observation mode, the intensities of the atomic lines of analytical and internal elements were increased with increasing sodium concentration. When potassium was co-existing, the intensities of the atomic lines of the analytical and internal elements were decreased with increasing sodium concentration in both the axial and radial observation modes. As a result, rhodium was very useful as an internal standard element, while yttrium was not. This effect could be caused by the differential of the ionization potential of the analytical elements and the internal-standard elements. The ionization potential of rhodium is similar to that of these analytical elements, while the ionization potential of yttrium is less than that of the analytical elements.