Purity.

The proportion of a sample that is the intended compound.

Purity is the fraction of a preparation that is the intended molecule rather than anything else. For peptides it is normally estimated by HPLC and expressed as a percentage of total peak area, with figures such as 98% or 99% commonly quoted. The impurities in a synthetic peptide are usually related substances left over from manufacturing: sequences missing an amino acid, sequences with an extra one, incompletely deprotected fragments, and residual solvents or salts from the synthesis and purification steps. Some of these are inert and some are not, and a percentage figure alone does not distinguish between them. Several qualifications matter more here than the headline number does. Purity is measured by a specific method with specific limits, and anything the detector cannot see does not appear in the total. Peptide content is a separate figure entirely, since a vial can be highly pure and still be mostly salt and water by mass. Purity says nothing about sterility, endotoxin, correct storage, or whether the molecule is the one claimed, which is an identity question. The misunderstanding worth correcting is reading a high purity percentage as a general quality or safety rating. It is one narrow chemical measurement among several that would be needed.