Femtomoles

A femtomole (fmol) is a unit of amount of substance in the International System of Units (SI). It denotes 10^-15 moles.

One fmol corresponds to about 6.02×10^8 molecules, using Avogadro’s number. This tiny quantity is commonly encountered in biochemical and analytical contexts where only trace amounts of material are available or required.

In relation to other prefixes, 1 fmol equals 0.001 picomol (pmol) and 1×10^-6 nanomol (nmol). Because the mole is a unit of amount and concentration depends on volume, the same amount can correspond to different concentrations: for example, 1 fmol in a volume of 1 microliter is equivalent to a concentration of 1 nanomolar (nM).

Applications and relevance: fmols are used to express small amounts of biomolecules such as peptides, oligonucleotides, proteins, and antibodies in research and diagnostics. They appear in contexts like mass spectrometry, quantitative proteomics, nucleic acid synthesis, and sensitive immunoassays, where measurements involve tiny sample quantities. Reported values may refer to the amount loaded onto a device, recovered after purification, or measured in a reaction mixture.

Measurement considerations: the practical use of femtomoles often depends on the analytical method’s sensitivity and the sample volume. It is important to distinguish between fmols (amount) and fM (femtomolar, a concentration). To convert between them, the volume must be known: concentration (M) = amount (mol) / volume (L).