Lab and analysis
Purity
Definition
How much of a material is the stated substance, usually given as a percentage and measured by a defined method.
A purity figure is only meaningful with its method and basis. 99 percent by HPLC area, 99 percent by titration and 99 percent on a dried basis can describe quite different products. Purity says nothing about which impurities make up the rest, which may matter more than the headline number.
When comparing offers, ask for the full specification and a recent certificate of analysis rather than the purity figure alone.
Related terms
- COA (certificate of analysis)A batch specific quality document listing the tests performed, the specification limits and the actual results.
- SpecificationThe list of tests, methods and acceptance limits a product must meet, agreed between supplier and buyer or set by a standard.
- AssayA quantitative test for the content of the main substance, and the result of that test on a certificate of analysis.
- Batch number (lot number)A code that identifies a quantity of product made in one production run, used for traceability.
- HPLCHigh performance liquid chromatography, the most common method for assay and impurity testing of organic chemicals and APIs.