Often prepared as a representative mixture of several different (usually @B00756@) @S05451@, and from which the @L03433@ is taken.
Source: PAC, 1988, 60, 1461. (Nomenclature, symbols, units and their usage in spectrochemical analysis-X. Preparation of materials for analytical atomic spectroscopy and other related techniques (Recommendations 1988)) on page 1465 [Terms] [Paper]