A GLP-1 certificate of analysis (COA) confirms what's actually in a vial: identity, purity, quantity, and residual contaminants tested by a named lab against a reference standard. Read it in this order — identity first, purity second, then quantity and the microbial/endotoxin lines — because a COA that skips identity confirmation is not a valid document, no matter how clean the purity number looks.
- A valid GLP-1 certificate of analysis lists identity (LC-MS), purity (HPLC), net peptide content, lot number, and test date — missing any one voids the document.
- Purity percentage alone means nothing without the identity confirmation sitting above it on the same COA.
- GLP-123 publishes third-party testing per lot so researchers can cross-check retention times and mass spec data against the reference standard.
- Endotoxin and residual solvent lines matter most for in vitro and in vivo protocols, less for simple stability comparisons.
- A COA older than the current lot, or one with no accreditation number for the testing lab, is a red flag worth escalating before you order.
Why this matters
Most buyers skim a COA for the purity percentage and stop there. That habit misses the two things that actually predict whether a vial matches its label: correct molecular identity and a batch-specific test date.
A vendor can print "99% pure" on a COA that tested the wrong molecule, or tested a different lot than the one shipped. The number only means something once the identity, lot, and date all line up with what's in your hand. GLP-1 research — mitochondrial function, gastric emptying, glucose-dependent insulin secretion, whatever the protocol — depends on knowing the exact compound and concentration going into the assay, not an approximate one.
How to interpret a GLP-1 certificate of analysis
Work through the document top to bottom. Each field either confirms the vial or raises a question you send back to the vendor before you use it.
| COA field | What it tells you | What to check |
|---|---|---|
| Identity (LC-MS or HPLC-MS) | Confirms the molecule is the labeled peptide, not a fragment or analog | Retention time and mass match the reference standards used |
| Purity (HPLC, % area) | Fraction of the sample that is the intended peptide vs. impurities | Reported as a specific percentage, not a vague "high purity" claim |
| Net peptide content | Actual peptide mass per vial after accounting for counterions and moisture | Distinguishes gross vial weight from usable peptide weight |
| Appearance | Physical description of the lyophilized powder | Matches expected color/texture for that peptide class |
| Residual solvents / moisture | Leftover processing chemicals and water content | Listed with a method reference (e.g., Karl Fischer) |
| Endotoxin / bioburden | Contamination relevant to cell-based and in vivo work | Present when the protocol involves live cultures or animal models |
| Lot number and date | Ties the COA to the specific vial shipped | Lot number on the COA matches the vial label exactly |
If any row is blank or vague, treat the COA as incomplete rather than assuming it passed silently.
Identity confirmation: the section most buyers skip
Identity testing, usually LC-MS or HPLC-MS, confirms the peptide's molecular weight and sequence match the labeled compound. This is the section that separates a real research peptide supplier from one reselling relabeled stock.
Without identity confirmation, a purity number is meaningless — you'd be measuring how pure an unknown substance is. A COA missing this section, or one that only shows a single HPLC chromatogram with no mass data, should be a dealbreaker for any protocol involving bioanalytical methods downstream.
Purity percentage: read the method, not just the number
HPLC purity is reported as a percentage of peak area under the curve. Two labs can report different purity numbers for the same lot depending on the column, gradient, and detection wavelength used — which is why the COA should name the method, not just print a bare percentage.
A purity figure with no method reference is not verifiable. Ask the vendor for the raw chromatogram if the COA only shows a summary number.
Quantity and net peptide content: the field most vendors omit
Vial weight and net peptide content are not the same thing. Lyophilized peptides carry moisture, counterions (acetate, TFA), and other residual mass that inflates the raw vial weight above the actual peptide content.
A COA that reports only "5mg vial" without a net peptide content adjustment is giving you the gross number, not the number your reconstitution math should use.
Microbial and endotoxin testing: protocol-dependent, not optional for cell work
Endotoxin and bioburden testing matter for in vitro assays involving cell cultures and any in vivo model — contamination here confounds results in ways a purity number never will. For simple physical stability comparisons, this section carries less weight, but it should still be present if the vendor is testing rigorously.
Why COA results vary between vendors and lots
- Testing lab differences — in-house testing vs. an accredited independent lab produces different confidence levels, even on the same peptide
- Method variation — HPLC gradient, column type, and detection method all shift the reported purity number slightly
- Lot-to-lot variability — even the same manufacturer's synthesis runs show small purity swings lot to lot
- Reference standard quality — identity confirmation is only as good as the reference standard the lab compares against
- Storage and handling before testing — a COA reflects the peptide's state at test time, not necessarily after shipping through cold chain conditions
- Reporting transparency — some vendors publish full chromatograms and mass spec traces; others summarize with a single number
“A purity percentage with no identity confirmation above it is not a certificate of analysis — it's a marketing claim with a decimal point.”
GLP-123 posts lot-specific COAs alongside listings so the identity and purity data a researcher checks matches the exact vial being shipped, not a generic batch reference. That practice sits inside a broader push toward third-party tested peptides for labs that need documentation they can attach to a protocol file in 2026.
Check lot-specific COAs before you order
Review identity, purity, and lot data for GLP-1 research peptides.
FAQ
What is a GLP-1 certificate of analysis?
A GLP-1 certificate of analysis is a lab document confirming a peptide vial's identity, purity, and quantity against a reference standard, tied to a specific lot number and test date. It's the only way to verify what's actually in a vial beyond the label.
How do I know if a COA is legitimate?
A legitimate COA names the testing lab, lists the method used for identity and purity (LC-MS, HPLC), and matches the exact lot number printed on the vial. If the lot number, date, or method are missing, the document can't be verified.
Is HPLC purity the same as net peptide content?
No, HPLC purity measures the fraction of the sample that is the intended peptide, while net peptide content accounts for moisture and counterion mass in the vial. A high purity percentage doesn't tell you how much actual peptide is in the vial.
Why do purity numbers differ between two vendors selling the same peptide?
Purity numbers differ because HPLC method, column type, and detection settings vary by lab, and lot-to-lot synthesis variation is normal even from the same manufacturer. Comparing numbers without comparing methods is not a valid comparison.
Does a COA need endotoxin testing?
Endotoxin testing matters most for in vitro work involving cell cultures and any in vivo model, where contamination can confound results independent of peptide purity. For simple physical or stability comparisons, its absence is less critical but still worth noting.
Can I request the raw chromatogram instead of the COA summary?
Yes, and it's worth asking for whenever a COA only shows a summary purity number without the underlying chromatogram or mass spec trace. A responsive vendor should provide the raw data on request.
What does 'lot-specific' COA mean?
A lot-specific COA is tested against the exact batch shipped, not a generic reference batch for that peptide type. Matching the lot number on the COA to the lot number on the vial label is the only way to confirm this.
One last thing
The field researchers skip most often — net peptide content vs. gross vial weight — is the one that throws off reconstitution math downstream. If your protocol assumes a concentration based on vial weight alone, you're working with a number that's already off by the moisture and counterion mass the COA should have disclosed separately. Check that line before you calculate a single dilution.
