The practical answer
Treat every new lot as a new documentation review. Match the container to a lot-specific certificate, then compare identity, HPLC purity, net peptide content, counterion, water and residual solvents line by line, checking that each uses the same method and units as last time. A matching product name or a high purity number does not resolve a missing or changed measurement.
Evidence, method & source dates ↓The short answer
Repeat orders are where documentation slips: people assume the new lot matches the old one. Bachem's quality-control guide shows why that fails. Identity, purity and content are separate questions measured by different methods, and net peptide content is not the same as purity because it also counts peptidic impurities and excludes counterions and moisture. [1]
This guide covers laboratory purchasing documentation only. It does not establish fitness for an experiment, medical suitability, or any use in people or animals. No supplier or lot was tested.
What each certificate line means and how it is measured
Methods below are those Bachem describes. If your certificate uses a different method, the numbers may not be comparable across lots. [1]
| Attribute | Typical method (Bachem) | What to compare between lots | Red flag |
|---|---|---|---|
| Identity | Mass spectrometry for molecular weight; amino acid analysis (gives composition, not sequence) | Expected vs observed mass; method named | Name matches but no identity data |
| Purity | Analytical HPLC, UV at 210 to 220 nm; main peak area as share of all peaks | Value, method, detection wavelength | Percentage with no chromatogram or method |
| Net peptide content | Share of peptide vs non-peptidic material, mostly counterions and moisture | Value and whether it is reported at all | Purity printed where content should be |
| Counterion | TFA by ion chromatography; acetate by HPLC or ion chromatography | Salt form and residual amount | Salt form changed without notice |
| Water | Karl Fischer titration | Value and units | Missing on one lot only |
| Residual solvents | Gas chromatography | Solvents listed and limits | New solvent appears |
| Document control | Not a test | Lot number, issue date, revision | Certificate lot differs from container |
Receiving checklist
- Container lot equals certificate lot equals packing slip lot.
- Certificate is dated and has a revision or document ID.
- Every attribute from the previous lot's certificate is present on the new one.
- Each attribute uses the same method and units as before, or the change is explained.
- Salt form (TFA, acetate, other) is stated and unchanged, or the change is documented.
- Differences are logged with the supplier's explanation, not smoothed over.
- Previous lot certificate is kept as a comparison record, not as evidence for the new lot.
Worked example: two invented lots
Lot 1 certificate: MS identity, HPLC purity 98.1% at 215 nm, net peptide content 78%, acetate salt, water 6%. Lot 2 certificate: MS identity, HPLC purity 98.6% at 220 nm, no net peptide content, TFA salt, no water value.
Lot 2's higher purity is the least important line. It dropped content and water results and changed counterion, and Bachem notes TFA cannot be completely removed because it forms a salt with the peptide. Record three open items: content missing, water missing, salt form changed. Ask the supplier for the missing results and confirmation of the salt form, and hold the lot until answered. [1]
Accept, hold or query
The responsible laboratory reviewer makes the decision; a checklist only exposes gaps. Keep return or replacement terms with the record so unresolved paperwork does not become an untracked cost. Sources accessed October 29, 2026.
| Situation | Status | Next action |
|---|---|---|
| All lines present, same methods, lots match | Ready for reviewer sign-off | Reviewer records acceptance and date |
| A line missing or method changed | Hold | Written request for the missing result or method explanation |
| Certificate lot differs from container | Hold | Request the correct certificate; do not edit your record |
| Salt form or identity result differs | Hold and escalate | Reviewer decides with supplier explanation on file |
| Supplier cannot supply a required result | Reject or return per terms | Record the reason and the return terms |
Questions before you decide
Can I reuse last lot’s certificate for a repeat order?
No. Match the received container to a lot-specific certificate, then compare identity, methods, purity, content, and document revisions separately. A familiar product name does not resolve a different lot.
Is a high purity percentage enough to accept a new lot?
Not by itself. Record missing or conflicting evidence for the laboratory reviewer. A high purity percentage does not establish identity, content, or experimental suitability.
Check the underlying evidence
Sources & review dates
- Bachem: Quality control of amino acids and peptides, a guide ↗Accessed 29 Oct 2026
Sources are documentary evidence. They do not establish firsthand testing of a listed supplier.