The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted standards.
A legnagyobb jelentőségű az International Union of Pure and Applied Chemistry (IUPAC) és a National Institute of Standards and Technology (NIST), habár nem mindegyik nevezhető általánosan elfogadott hivatkozási alapnak.