Purity explained · September 19, 2026
What does “99% purity” mean on a peptide COA?
It can be a useful chromatographic result. It is not proof of identity, labeled vial content, sterility, low endotoxin, or a complete contaminant screen.
THE SHORT ANSWER
Purity is one result inside a larger evidence chain.
When a peptide certificate reports 99% purity by HPLC, it usually means the laboratory attributed roughly 99% of the integrated chromatographic signal—under that procedure—to the target peak. The exact interpretation depends on the method and report.
That figure does not automatically identify the compound, weigh the contents of the vial, match the certificate to inventory, or test for microbes, endotoxin, metals, solvents, or every possible adulterant. Those conclusions need their own evidence.
DO NOT COLLAPSE THESE RESULTS
Four numbers that answer four different questions.
- 01Identity — is the target compound detected?
- 02Purity — how dominant is the target signal under the stated separation?
- 03Content — how much target material was measured?
- 04Safety-related panels — what microbes, endotoxin, metals, solvents, or targeted contaminants were tested?
Which method produced the percentage?
A purity number should stay attached to its method. HPLC-UV separates components under a stated chromatographic procedure and reports the target peak relative to the detected signal. The result is method-specific: column, detector, wavelength, integration, reference material, and the method's ability to separate nearby impurities all matter.
Can you find the method—not only the percentage?
Was identity tested separately?
A clean chromatogram does not independently establish that the main peak is the peptide named on the label. A separate identity result—often mass spectrometry or another orthogonal procedure—addresses a different analytical question. ICH Q2(R2) treats identity, impurity or purity testing, and assay or content as distinct measured attributes.
What result ties the main signal to the claimed compound?
Was the amount in the vial measured?
A certificate can describe a sample as “10 mg” while never measuring net content. Chromatographic purity describes the relative composition of the detected sample; it does not automatically establish that the vial contains the labeled mass. Look for a numerical net-content, assay, potency, or quantitative result.
Is the amount a laboratory result—or copied from the label?
Does the certificate match the exact lot?
Even a technically strong report applies to the sample and lot identified on the document. Match the supplier or client, product, lot, accession or report number, dates, and verification code. A real certificate for another batch is not evidence for the lot in front of you.
Can the report be connected to this exact lot without guessing?
Which separate panels are missing?
Sterility or microbial screening, endotoxin, heavy metals, residual solvents, and targeted adulterants require their own procedures. A 99% HPLC result cannot silently stand in for tests that were not performed. List every absent category beside the headline number.
What important question did this laboratory never test?
Are the limits and numerical results visible?
A useful certificate identifies the test, method, acceptance limit, and numerical result where applicable. FDA's Q7A guidance describes those fields for regulated active pharmaceutical ingredients. Research-use sellers are not automatically operating under that framework, but the document principles remain a useful benchmark for reading what is present and absent.
Does “pass” have a visible method, limit, unit, and result behind it?
REAL DOCUMENT, NARROW CONCLUSION
ANKR Lab’s 99.23% certificate shows the distinction.
Freedom Diagnostics reported BPC-157 identity by LC-MS and 99.23% purity by HPLC-UV for lot 3001. The same certificate says net content was not requested and contains no sterility, endotoxin, or broader contaminant results. Compound IQ scores the visible document 3/7.
COMMON QUESTIONS
Keep each conclusion tied to the test that produced it.
Does 99% purity mean the vial is 99% peptide by weight?
Not necessarily. A chromatographic area-percent result is not automatically a gravimetric or net-content measurement. Read the method and look for a separate quantitative content result.
Can a sample be 99% pure but contain the wrong amount?
Yes. Purity and measured quantity answer different questions. A sample can have a dominant target peak while the vial contains more or less material than the label states.
Does 99% purity prove sterility or low endotoxin?
No. Sterility or microbial screening and endotoxin testing require separate methods and results.
Is LC-MS the same as HPLC purity?
No. They may be coupled in one workflow, but identity by mass spectrometry and chromatographic purity remain distinct conclusions that should be reported separately.
PRIMARY SOURCES
The analytical framework behind the distinction.
- ICH Q2(R2) ↗Treats identity, impurity or purity testing, and assay or content as distinct analytical attributes and emphasizes method specificity.
- FDA Q7A guidance ↗Describes batch certificates that identify the tests performed, acceptance limits, numerical results, dates, and accountable issuer in regulated API settings.
- FDA peptide API warning letter ↗Illustrates why chromatographic resolution, peptide-related impurity characterization, orthogonal methods, and bacterial-endotoxin validation remain separate concerns.
FREE TWO-PAGE REFERENCE
Keep all seven checks beside the purity number.
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