1997 Volume 83 Issue 3 Pages 181-186
For the analysis of trace elemental constituents by glow discharge mass spectrometry, ion beam ratios (IBRs), ratios of ion currents of analysed elements to that of matrix element, are observed. In general, IBRs are affected by the shape for pin-shaped samples or the size of mask for disk-shaped samples. These effects were studied systematically for Febased alloys. For disk-shaped samples, IBRs are rather independent of the mask size provided that the diameter is in the range of 10-15mm. For pin-shaped samples, IBRs depend on the sample shape. However, it has been shown that IBRs for arbitrary shapes can be corrected to that of a standard shape using an experimental equation. The equation for correction is a linear combination of r, L and L2 and F, where r and L are diameter and discharge length of pin-shaped samples, respectively, and F is a parameter for the shape of cross section. IBRs depend on r linearly. On the other hand, they are dependent on the second order of L. The fact indicates that there exists a discharge length (Lext) for each element giving the IBR an extremum. LextS are 3-6mm for the most elements. By using sample whose discharge length is close to Lext, it is possible to minimize the effect of discharge length on IBRS. The present correction shows the possibility to reduce the coefficient of variation for samples of arbitrary shapes from 40% to less than 10%.
