Semaglutide Research Guide: Structure, COA and Handling
Semaglutide is a 31-amino-acid synthetic analog of glucagon-like peptide-1 (GLP-1) that activates the GLP-1 receptor. Labs use it as a reference GLP-1 receptor agonist in receptor-signaling assays and as the single-receptor comparator in studies of dual and triple agonists. This page covers its structure, what a semaglutide certificate of analysis should show, and how to handle the lyophilized powder, using FRO Peptides’ own published lot reports as the example.
Semaglutide at a glance
| Class | GLP-1 receptor agonist (research compound) |
|---|---|
| Length | 31 amino acids, based on human GLP-1 (7-37) |
| Molecular formula | C187H291N45O59 |
| Molecular weight | ≈ 4,113.6 g/mol |
| CAS number | 910463-68-2 |
| Key modifications | Aib (α-aminoisobutyric acid) at position 8; Arg at position 34; C18 fatty diacid on Lys26 via a γGlu–2×OEG linker |
| Supplied as | Lyophilized white powder in sealed vials |
| FRO vial sizes | 2mg, 5mg, 10mg, 15mg |
| FRO tested purity | 99.56% (5mg, 53HL-2K5R) and 99.57% (10mg, LUNJ-TF4K), HPLC |
How the molecule is built
Native GLP-1 is cut apart within minutes by the enzyme DPP-4, which cleaves it after position 8. Semaglutide swaps that alanine for Aib, a non-natural amino acid the enzyme can’t cut. A second change, lysine to arginine at position 34, leaves a single lysine (position 26) for attaching the side chain. That side chain is an 18-carbon fatty diacid on a short linker, and it binds albumin. The result is a GLP-1 analog that stays intact far longer in biological matrices than the native peptide.
For lab work this matters in two ways. The fatty acid side chain is part of the molecule’s identity, so a sample with the backbone but a missing or damaged side chain is not semaglutide. And the lipid portion makes the molecule more sensitive to aggressive mixing and repeated freeze-thaw than a plain peptide of the same length.
Why labs use it
- GLP-1 receptor pharmacology. Its activity at the GLP-1 receptor is well characterized in the published literature, so it is a standard positive control in receptor-binding and cAMP-signaling assays.
- Comparator work. It is the single-receptor reference point when characterizing dual and triple agonists such as tirzepatide and retatrutide.
- Lipidation and stability studies. It is a textbook example of how a fatty-acid side chain and albumin binding change a peptide’s stability, and it is used as a model compound in that work.
How to read a semaglutide certificate of analysis
A COA is only useful if you know what each line proves. FRO has two semaglutide reports on file from AccuMark Labs, both received 03/02/2026 and published 09/07/2026:
| Test | 5mg (53HL-2K5R) | 10mg (LUNJ-TF4K) | What it tells you |
|---|---|---|---|
| Identity | Semaglutide, conforms | Semaglutide, conforms | The main compound in the vial matches semaglutide. |
| HPLC purity | 99.56% | 99.57% | Share of the sample that is the target peptide, measured by UV at 220 nm, against a spec of more than 98.0%. Both chromatograms show one sharp main peak at about 5.6 minutes. |
| Quantity | 6.14 mg in a 5 mg vial | 11.96 mg in a 10 mg vial | How much peptide is actually in the vial. Both lots were overfilled, by about 23% and 20%. Many COAs skip this line, but it is the one that catches underfilled vials. |
Both full reports, chromatograms included, are free to open in the Semaglutide COA library. Match the code on your vial to the right report.
HPLC purity vs. structural confirmation
HPLC purity tells you how clean the sample is. It does not, on its own, prove every part of the structure is intact. For a lipidated peptide like semaglutide, mass spectrometry is the method that confirms the full molecular weight, including the fatty acid side chain. FRO’s current semaglutide reports cover identity, HPLC purity and measured quantity. FRO has semaglutide testing underway at Vanguard Laboratory, an ISO 17025 lab, and the results will be added to the COA library when they come in.
Red flags on any supplier’s COA
- No lot or sample code, or a code that doesn’t match the vial.
- No lab name, or a lab you can’t find.
- Purity with no chromatogram.
- No measured quantity, only the label claim.
- One report covering every vial size, when the sizes are filled from different lots.
- The same report reused across several products or years.
Storage and handling for research use
- Lyophilized powder: store frozen (−20 °C), sealed and protected from light. Let the vial reach room temperature before opening to avoid condensation.
- Reconstitution: add bacteriostatic water slowly down the vial wall and swirl gently. Don’t shake, because agitation can damage the lipidated side chain. Use the peptide reconstitution calculator to work out concentration for your protocol.
- After reconstitution: refrigerate at 2–8 °C, protect from light, and use within your protocol’s defined window.
- Avoid repeated freeze-thaw. If you need to store reconstituted material frozen, split it into single-use aliquots first.
Frequently asked questions
Does FRO Peptides publish a COA for semaglutide?
Yes. Reports for the 5mg and 10mg lots from AccuMark Labs, an independent lab, are in the COA library, chromatograms included.
What purity is FRO’s semaglutide?
The current lots tested at 99.56% (5mg) and 99.57% (10mg) by HPLC, against a specification of more than 98.0%.
How is semaglutide different from tirzepatide and retatrutide?
Semaglutide activates one receptor (GLP-1). Tirzepatide activates two (GIP and GLP-1), and retatrutide activates three (GIP, GLP-1 and glucagon). All three carry a fatty-acid side chain.
What is the difference between the vial sizes?
Only the quantity of peptide. The 2mg, 5mg, 10mg and 15mg vials contain the same compound.
Is semaglutide from FRO for human use?
No. FRO sells semaglutide strictly for laboratory and analytical research. It is not for human or veterinary use.
View Semaglutide research peptide (2mg–15mg) →
Lot reports published in the COA library. Ships next business day, FedEx 2-Day.
For laboratory research use only. Not for human or veterinary use. Not a drug, food, or cosmetic under FDA regulations. Nothing on this page is medical advice.