The status of metallurgical micro-sampling and analysis is reviewed. Spectroscopic detectabilities for several metallic elements are found to be of the order of 1 × 10−9 gram when employing a quartz Littrow spectrograph together with arc excitation and Eastman 103-O emulsion. Techniques are described for the removal and identification of milli-microgram quantities of metallic constituents by means of drills as small as 6.3 microns diameter.
E. F. Runge and F. R. Bryan, "Micro-Analysis of Metals by Optical Emission Spectroscopy," Appl. Spectrosc. 13, 74-76 (1959)