Any element having an average concentration of less than about 100 parts per million
atoms
(
) or less than

.
Source:
PAC, 1979, 51, 2243
(General aspects of trace analytical methods - IV. Recommendations for nomenclature,
standard procedures and reporting of experimental data for surface analysis techniques)
on page 2246
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.