# Peptide content: certificate-of-analysis checklist

Peptide Care Index · Sources checked October 14, 2026

Use this before entering a report's values into the peptide content calculator.

1. **Match the material.** Confirm the sample or batch ID. Do not combine a mass from one sample with an assay from another.
2. **Identify the mass.** Is the mg figure gross powder, total peptidic material, target peptide, or a nominal label claim? Gross powder excludes the container.
3. **Define the percentage.** Is “content” total net peptide content, target-specific mass fraction, raw nitrogen, HPLC area purity, or percentage of a label claim?
4. **Match the basis.** Is the result for the as-received sample, dry material, anhydrous material, or another basis? Ask the laboratory to reconcile different bases.
5. **Check the purity method.** What signal is included? Does the laboratory support using this purity value with the content measurement? An HPLC area fraction is not automatically a precise mass fraction.
6. **Keep uncertainty.** Record the lab's uncertainty, detection/quantitation limits and sampling qualifications where supplied. Calculator digits do not replace them.

## Choose the matching calculation

| What the report supplies | Calculation |
|---|---|
| Gross powder mg plus total net peptide content % | Total peptidic mg = gross mg × NPC/100 |
| The above plus a suitable HPLC purity % | Estimated target mg = total peptidic mg × HPLC purity/100 |
| Total peptidic mg already reported | Do not apply NPC again; apply a suitable target-purity factor only if justified |
| Target-specific % by weight of as-received powder | Target mg = gross mg × target mass fraction/100; no additional purity factor |
| Target-specific mg already quantified | Use that reported target amount; no additional factor |
| Only HPLC purity, or an unclear definition | Ask for the missing quantity; do not assume 100% content |

Do not enter raw nitrogen percentage as NPC. Do not subtract water/TFA mass percentages from HPLC area purity. Do not infer underfilling, sterility, safety or clinical effect from a content calculation alone.

## Sources

- Bachem, analytical definitions and formula: https://www.bachem.com/knowledge-center/faq-frequently-asked-questions/
- GenScript, content definition and separate purity factor: https://www.genscript.com/accupep_quality.html
- Biosynth, net-mass vialing example: https://www.biosynth.com/peptides/peptide-manufacturing/analytics
- ICH Q2(R2), analytical validation and response factors: https://database.ich.org/sites/default/files/ICH_Q2(R2)_Guideline_2023_1130.pdf
- Elementar, nitrogen-to-NPC conversion: https://www.elementar.com/en/blog/gmp-in-use-even-the-smallest-sample-quantities-are-sufficent

Original checklist and calculation guide by Peptide Care Index. Reuse with credit to Peptide Care Index; underlying sources retain their own attribution and terms. Reference page: https://peptidecareindex.com/research/peptide-content-calculator/.