When a dc arc is used for trace analysis on a spectrometer, calibration curves with a pronounced toe due to spectral background are found. For analysis of high purity materials it is most important that linear relationships should be established to ultra-trace levels when total impurity content is specified within the ppm level. A solution to this problem is outlined and the linear relationships obtained for, copper, bismuth, and cadmium in high purity silver to 0.1 ppm are shown. An electronic circuit is described that enables these background corrections to be made.
B. S. Cooper and D. J. Hobbs, "The Use of the Direct Reading Spectrometer with dc Arc Excitation and Total Sample Combustion in the Analysis of High Purity Materials," Appl. Spectrosc. 25, 60-64 (1971)