Ask what each number measures
A report can contain several accurate numbers that describe different properties. Before comparing them, identify the unit and the method. A percentage, a milligram quantity and a molecular mass in daltons are not competing estimates of the same thing.
| Term | Question it addresses | What to avoid assuming |
|---|---|---|
| Chromatographic purity | What proportion of the integrated response is assigned to the main component? | That it is automatically the peptide’s percentage of total powder weight. |
| Measured quantity or assay | How much analyte was measured under the stated method? | That it can be calculated from the purity figure alone. |
| Peptide content | What fraction or amount is defined as peptide by the reporting method? | That every laboratory uses the term on the same basis. |
| Gross powder weight | How much total material is present? | That all of that mass is the target peptide. |
| Nominal amount | What amount describes the sample or label? | That it is the actual measured result. |
Read a real purity and quantity result
The examples below come from reports already published in Aera’s lab-results archive. They are historical report examples, not a statement about current inventory or the lot in a particular order. The original laboratory and client names are retained. Ask Aera to confirm the applicable lot if you need documentation for supplied material.
The MZ Biolabs Tesamorelin certificate identifies lot USA1262 Vial 1. Its title describes 10 mg, while its analytical results report 99.92% purity and 10.42 mg/vial measured quantity. These values occupy different fields because they answer different questions.
The purity percentage agrees with the main peak’s area percentage in the report’s peak list. The quantity is separately labelled as quantification by HPLC-UV. The report does not give the total powder weight, so it does not support calculating the target peptide as a percentage of that total weight.
Why powder weight can differ from peptide amount
Peptide preparations can include counterions and residual moisture. Depending on the preparation, other components can also contribute to the material’s weight. Bachem’s technical guidance explicitly distinguishes HPLC purity from peptide content and notes the role of counterions and moisture.
The MZ Biolabs report includes a note that salts and sugars are not normally detected using UV. That is a reminder that a detector does not respond equally to every possible component. It is not a measured inventory of the contents of this particular sample.
If the required question is the peptide fraction of total material, request a result that actually establishes that quantity, together with its method and reporting basis. A chromatographic percentage alone is not enough.
High purity can coexist with a different assay amount
A second example is the TrustPointe report for BPC-157 batch 1305. It lists 99.817% purity alongside a 9.22 mg assay for SPL-1742-S01, and 99.993% purity alongside a 9.30 mg assay for SPL-1742. The sample name describes 10 mg vials.
The lesson is the distinction between measurements. These reported amounts do not justify a conclusion about every vial in a lot. Nor should this article decide compliance with an unstated specification: that requires the applicable acceptance criteria and method context.
Keep the sample columns intact when quoting them. The batch verification guide shows the identifiers and the laboratory’s printed verification route.
Compare reports on the same basis
- Compare the same compound and formulation.
- Check whether the result is a percentage, concentration or amount per vial.
- Read the method and any stated calibration or reference basis.
- Preserve the sample identifier and reporting precision.
- Ask about uncertainty and acceptance criteria when they matter to your work.
Small numerical differences between reports are not a useful league table without comparable methods and context. More decimal places do not automatically mean stronger evidence.
Keep identity separate too
Purity does not replace identity evidence. A well-separated main peak still needs an appropriate basis for assigning it to the intended compound. The Tesamorelin report supplies a separate mass-based identity section on page two.
Read the comparison of HPLC and mass spectrometry to see how those two pages fit together. For the complete document checklist, start with the COA reading guide.
Common questions
Does 99% purity mean 99% of the powder is peptide?
Not necessarily. The method and reporting basis determine what the percentage means. A chromatographic area percentage is not automatically a mass fraction.
Can I calculate measured quantity from the label and purity?
No. That calculation assumes relationships the report may not establish. Use the separately reported quantity or request suitable quantitative testing.
Is purity the same as potency?
No. An analytical purity result is not a measurement of biological activity or clinical effect.
Sources and original reports
- MZ Biolabs: USA1262 Vial 1, purity and quantity results
- TrustPointe Analytics: batch 1305, separate purity and assay rows
- Bachem: Care and Handling of Peptides, net peptide weight section
Report examples checked against the public files on 14 October 2026. Laboratory authorship of a source report does not imply review or endorsement of this article.