A simplified dilution method is described for the analysis of powdered samples of unknown origin and composition. The sample is mixed with an equal amount of graphite powder containing the reference element, germanium. A small amount of this mixture is placed in a 1-mm-deep, 1-mm-diameter crater drilled in the end of a 3/16-inch graphite electrode. Apparently, the diluent is essentially provided by the electrode during arcing. This rapid approximate method has an average accuracy that is acceptable for many purposes. The method also permits the determination of the relative amounts of the elements in a very small sample (ca 1 mg).
H. E. BIBER and S. LEVY, "Spectrographic Procedure for Analysis of Powdered Samples of Unknown Origin," J. Opt. Soc. Am. 47, 381-385 (1957)