What “≥99%” can mean
In research peptide catalogs, a high purity figure (for example, a claim styled as ≥99%) is frequently based on HPLC peak area percent under a stated chromatographic method: the main peak’s share of total integrated peak area among species detected under those conditions.
That number is useful when method, detector, and integration rules are known. It is not automatically the same as absolute peptide content by weight, bioassay activity, or free-base peptide content after accounting for salt and water.
Method dependence
HPLC purity depends on column chemistry, gradient, temperature, detection wavelength, sample preparation, and how peaks are integrated. Changing any of these can change reported area percentages—even for the same physical sample.
Comparing purity numbers across suppliers without method context is therefore unreliable. Lot CoAs that include method notes or chromatograms are more informative than a bare marketing percentage. See HPLC and Mass Spectrometry and How to Read a CoA.
Salt form, free base, and water
- Salt vs free base: Many peptides are supplied as salts. Counter-ions contribute mass that is not “peptide free base.” HPLC area % of a UV-active peptide peak does not by itself subtract counter-ion mass.
- Water content: Lyophilized materials can contain residual or absorbed water. Moisture affects weighing and concentration calculations without necessarily appearing as a separate HPLC impurity peak.
- Net peptide content: Some laboratories report net peptide content using additional assays. When that metric is needed, request the specific result on the lot documentation rather than assuming it equals HPLC purity.
Related substances
Peaks other than the main component may be described as related substances, process-related impurities, or degradation products depending on the lab’s terminology. Resolution limits of the method determine what can be seen. Low-level species below the method’s detection or reporting thresholds will not appear in the purity calculation.
Why VialVibes does not display unverified purity % on product cards
Catalog cards and product pages at VialVibes intentionally avoid fixed purity percentages that are not tied to a specific lot CoA published for that unit. Reasons include:
- Purity is lot- and method-dependent;
- Displaying a generic “≥99%” without lot documentation can overstate certainty;
- Buyers who need analytical evidence should review the CoA for their lot.
Product pages state that a lot-specific Certificate of Analysis is available on request when available. Request documentation via coa.html. Our broader posture is described on Quality & Compliance.