In artificially prepared standards analyzed by our dc arc emission spectrometric technique, copper showed very poor precision for repeated analyses at any concentration between 1 and 100 ppm. Similar observations for copper, and only copper, in graphite-based graded standards containing 60 elements, have been reported by Chaney. Mitteldorf has also reported that similar complaints have been made regarding copper inconstancy in prepared standards. It is the purpose of this note to report our solution to this problem in the hope that it may be of value to other spectrographers faced with the same problem.
Geoffrey Thompson and Donald C. Bankston, "Apparent Copper Inconstancy in Artificially Prepared Standards when Determined by Emission Spectrometry," Appl. Spectrosc. 24, 375-378 (1970)