Purity
The mass fraction of the desired substance in a sample, usually expressed as a percentage of the total mass.
Formula / equation
purity % = (mass of pure substance / total mass) × 100
Unit
Dimensionless
In depth
Purity is assessed by melting-point range, chromatographic peak area, titration against a primary standard or spectroscopic analysis. Because a sharp melting point is destroyed by even small impurities, a narrow melting range remains one of the fastest indicators of a well-purified organic solid.
Examples in the real world
A pharmaceutical active ingredient specified at ≥99.5%, or a 4 g sample containing 3.8 g of product being 95% pure.