Semaglutide Testing: Purity, Identity, and COA Verification
Complete guide to testing semaglutide with HPLC and mass spectrometry: purity standards, molecular weight verification, ...
Why Semaglutide Requires Independent Testing
Semaglutide is a GLP-1 receptor agonist with a molecular weight of 4,113.58 Da. It is one of the most widely purchased research peptides, and unfortunately one of the most counterfeited. Independent laboratory testing using HPLC and LC-MS is the only reliable way to verify that a semaglutide sample matches its label claims.
HPLC Purity Analysis for Semaglutide
Reverse-phase HPLC on a C18 column separates semaglutide from its impurities and degradation products. The purity is calculated as the area percentage of the main peak relative to all peaks in the chromatogram.
- Research grade: ≥98% purity
- Pharmaceutical grade: ≥99.5% purity
- Acceptable: 95-98% with documented impurity profile
- Unacceptable: Below 95% or multiple undefined peaks
LC-MS Identity Verification
The theoretical molecular weight of semaglutide is 4,113.58 Da. LC-MS confirms identity by measuring the actual molecular weight and comparing it to this theoretical value. A match within ±0.1% confirms the sample is semaglutide.
Common substitutions include liraglutide (3,751.20 Da) and tirzepatide (4,813.52 Da). These are sometimes sold as semaglutide because they are in the same drug class but differ in potency and price.
Common Semaglutide Adulterants
- Liraglutide substitution: Cheaper GLP-1 analog sold as semaglutide. Detectable by LC-MS — mass difference of 362 Da.
- Bacteriostatic water dilution: Vial contains less peptide than labeled. Detectable by fill weight measurement.
- Salt addition: Sodium chloride or mannitol added to increase weight without adding peptide.
- Degradation products: Semaglutide degrades when stored above -20°C, producing truncated fragments visible as extra HPLC peaks.
Semaglutide COA Checklist
A valid semaglutide COA must include:
- Batch number and manufacturing date
- HPLC chromatogram with purity percentage
- LC-MS mass spectrum with measured vs. theoretical mass
- Fill weight (net content of vial)
- Appearance description
- Storage conditions and shelf life
- Laboratory name, accreditation, and analyst signature
FAQ: Semaglutide Testing Guide
What is the molecular weight of semaglutide?
The molecular weight of semaglutide is 4,113.58 Da. LC-MS should show this value within ±0.1% to confirm identity.
How accurate is HPLC for semaglutide purity?
HPLC with UV detection at 214 nm is highly accurate for peptide purity, typically with ±0.5% precision. The method detects impurities above 0.1% of the main peak area.
Can I tell if my semaglutide is real without lab testing?
No. Visual inspection cannot distinguish genuine semaglutide from counterfeits. Only HPLC purity analysis and LC-MS identity confirmation can verify authenticity.
Related Resources
- Ipamorelin Testing Guide
- CJC-1295 Testing Guide
- Third Party Testing Lab
- TB-500 Testing Guide
- BPC-157 Testing Guide
- How Peptide Testing Works — understand HPLC, LC-MS, purity, identity, and fill weight
- HPLC vs LC-MS for Peptide Testing — when to use each method
- Identity, Purity, and Fill Weight Explained — what each metric means
- Peptide Testing FAQ — common questions about testing peptides
- Request a Free Peptide Test — send your sample for independent HPLC analysis
Get Your Peptide Tested — Free
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