Nomenclature and SI Guidelines

SI (Système International) units 
should be used. 
Only symbols (not their subscripts, superscripts or description in brackets) of physical quantities should be written in italic. All physical quantities given in table columns or rows or on figure axes should conform to the algebraic rules, i.e. physical quantity/unit=numerical value. Numerical values and their units must be written with one space between (e.g. 1 cm, 2 L, 3 g/L, 10 %, 20 °C).

For the mixtures of A (solute) and B (solvent) the content should be expressed with one of the physical quantities given in the table below (the content itself is not a physical quantity).

Name Symbol Definition SI unit
Mass ratio ζ ζ(A,B)=m(A)/m(B)  1
Volume ratio Φ Φ(A,B)=V(A)/V(B)   1
Amount (of substance) ratio  r r(A,B)=n(A)/n(B)   1
Number ratio R R(A,B)=N(A)/N(B)   1
Mass per volume ratio m/V m(A)/V(B)  kg/m3


Mass fraction w w(A)=m(A)/[m(A)+m(B)]  1
Volume fraction φ φ(A)=V(A)/[V(A)+V(B)]  1
Amount fraction x x(A)=n(A)/[n(A)+n(B)]  1
Number fraction X X(A)=N(A)/[N(A)+N(B)]  1


Mass concentration γ γ(A)=m(A)/[V(A)+V(B)]  kg/m3
Volume concentration σ σ(A)=V(A)/[V(A)+V(B)]  1
Amount concentration c c(A)=n(A)/[V(A)+V(B)]  mol/m3
Number concentration C C(A)=N(A)/[V(A)+V(B)]  1/m3
Molality  b b(A,B)=n(A)/m(B) mol/kg

The principle to use as few characters as possible is recommended. Authors should use units with SI prefixes instead of the basic SI unit (e.g.instead of 1.2·10–6 A, 1.2 μA should be used). For volume, the unit litre (1 L) or its decimal units are recommended as a special name for 1 dm3 (1 L=1 dm3). Following the same principle, although not recommended by IUPAC, the unit 1 M (or its decimal units) for amount concentration can be used (1 M=1 mol/L). The symbols w/w, v/v and w/v should not be used. The proper way for expressing fraction is: % (by mass), % (by volume) or % (m/V). Ppm and ppb should also not be used, instead write 10–6, 10–9, etc. Centrifugal force should be expressed as times gravity (×g), not rpm.

The IUPAC recommendations on chemical nomenclature should be followed (see:

For the biochemical nomenclature including abbreviations, recommendations of the Nomenclature Committee of IUBMB and the IUPAC-IUBMB Joint Commission on Biochemical Nomenclature ( should be followed.

For gene nomenclature and symbols, the Human Genome Nomenclature Database ( and Entrez Gene ( should be consulted.

Apart from the recommended nomenclature, the usual common terms are acceptable as is the use of the usual abbreviations within the text, particularly in cases of compounds of very long names.


«« | Tables and Figures Guidelines                                                                                                          References Guidelines | »»