Parts per Billion
A concentration unit expressing one part of solute per thousand million parts of solution.
Formula / equation
ppb = (m_solute / m_solution) × 10⁹
Unit
ppb
In depth
Equivalent to one microgram per litre in dilute aqueous solution, ppb is used where toxicity occurs at extremely low levels. Measurement at this level demands trace-analysis techniques such as ICP-MS and scrupulous avoidance of contamination from glassware and reagents.
Examples in the real world
A drinking-water limit for arsenic of 10 ppb; mercury in fish tissue reported in ppb.