micromol

Micromol (symbol μmol) is a unit of amount of substance in the International System of Units (SI). It denotes one millionth of a mole: 1 μmol = 1 × 10^-6 mol. Because a mole contains Avogadro’s number of entities, 1 μmol corresponds to about 6.022 × 10^17 molecules or other specified entities.

The micromol is commonly used for small quantities in chemistry, biology, pharmacology, and environmental science. In solution chemistry, concentration is often expressed in micromolars (μM), defined as micromoles per liter; 1 μM equals 1 × 10^-6 mol per liter. The term micromol refers to amount of substance, while micromolar refers to concentration.

Conversions and relation to other units: 1 μmol equals 0.001 mmol or 0.000001 mol. The mass corresponding to 1 μmol depends on the substance’s molar mass M (g/mol): mass = n × M = 1 × 10^-6 × M grams. For example, 1 μmol of glucose (molar mass about 180.16 g/mol) has a mass of approximately 0.180 mg.

Prefixes and notation: The micro prefix denotes 10^-6, so micromol is a submultiple of the mole. It is typically written as μmol, with the Greek letter mu. In practice, care is needed to distinguish micromol from micromolar, since the former concerns amount of substance and the latter concerns concentration.