How to Read a Certificate of Analysis for an Aroma Material
The numbers that matter, the ones that are noise, and how to compare two suppliers' certificates fairly.
Assay is the headline number
Assay, stated as a percentage with the analytical method, is the purity of the material. But a supplier quoting 99.5% by gas chromatography and another quoting 99.5% by a different method are not necessarily comparable - always check the method is named.
Isomer ratios matter more than total assay
For materials such as citral, linalool and the terpene families, the isomer ratio usually matters more to your formula than the total purity. A citral at 95% assay with a neral/geranial ratio of 60/40 performs differently from one at 95% with a 50/50 ratio.
Water content is a stability indicator
Water content is cheap to measure and it predicts a lot. Higher water content means more headspace oxidation and a shorter practical shelf life, particularly for materials with aldehyde or ester groups.
Compare certificates on the same footing
When you compare two suppliers, align them: same method, same reporting units, same reference temperature for density and refractive index, and the same set of parameters requested.
Ask what is not on the certificate
A good supplier will tell you which parameters they do not measure routinely. Those are the ones to negotiate on before the trial order, not after.