The discrete identifiable portion suitable for taking as a sample or as a portion
of a sample. These units may be different at different stages of sampling.
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
on page 1463
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