Density is frequently a quantity divided by volume: mass density or mass concentration is mass per volume, M·V-1 [kg·m-3]; radiant energy density is radiant energy per volume, Q·V-1 [J·m-3]; charge density is charge per volume, Q·V-1 [C·m-3]. However, electric current density is current divided by area, j=I·A-1 [C·m-2]. Number density of entities or number concentration is numbers per volume, CB = NB·V-1 [x·m-3]. In contrast, the amount-of-substance concentration, cB = nB·V-1 [mol·m-3] is not called a substance density (IUPAC). Thus the sample mass concentration is CmX = mX·V-1 [kg·m-3], the mitochondrial concentration is CmtE = mtE·V-1 [mtEU·m-3], whereas the specific mitochondrial density is DmtE = mtE·mX-1 [mtEU·kg-1], and the mitochondrial content per object X is mtENX = mtE·NX-1 [mtEU·x-1] (Gnaiger 2019 MitoFit Preprint Arch).
Abbreviation: ρ, C, D
MitoPedia concepts: Ergodynamics