73% of Peptides We Test Show Purity Discrepancies vs. Supplier Claims
73% of peptide samples submitted to ACS Peptide Testing Labs for independent verification show measurable purity discrepancies compared to the supplier's Certificate of Analysis (COA). This finding is based on our analysis of over 1,200 peptide samples tested between 2024 and early 2026.
This article presents the full breakdown of our data, which peptide categories are most affected, the average size of discrepancies, and the most common types of impurities we detect.
Summary of Key Findings
- 73% of samples show purity lower than supplier claims
- Average purity discrepancy: 8.4 percentage points below claimed purity
- 41% of samples have discrepancies greater than 10 percentage points
- 17% of samples contain detectable levels of heavy metals (lead, cadmium, or mercury)
- GLP-1 receptor agonists (Semaglutide, Tirzepatide) show the highest discrepancy rates at 81%
- Only 27% of supplier COAs exactly matched our independent results
Purity Discrepancy by Peptide Category
Our data reveals significant variation across peptide categories. The following statistics reflect samples tested at ACS Peptide Testing Labs using validated RP-HPLC methodology:
GLP-1 Receptor Agonists (Semaglutide, Tirzepatide, Retatrutide)
- Samples tested: 340+
- Discrepancy rate: 81%
- Average purity gap: 11.2 percentage points
- Most common issue: Truncated sequences and oxidation byproducts
- Samples below 90% actual purity: 38%
GLP-1 peptides are the most frequently misrepresented category we test. The complexity of these molecules. Semaglutide is a 31-amino-acid peptide with a fatty acid chain, makes them difficult to synthesize at high purity, yet many suppliers claim 98-99% purity.
Research Peptides (BPC-157, KPV, Thymulin, Epitalon)
- Samples tested: 420+
- Discrepancy rate: 69%
- Average purity gap: 7.1 percentage points
- Most common issue: Incomplete deprotection and deletion sequences
- Samples below 90% actual purity: 24%
Metabolic Peptides (NAD+, MOTS-c, 5-Amino-1MQ)
- Samples tested: 280+
- Discrepancy rate: 64%
- Average purity gap: 6.3 percentage points
- Most common issue: Degradation products from poor storage/shipping
- Samples below 90% actual purity: 19%
Custom/Specialty Peptides
- Samples tested: 160+
- Discrepancy rate: 58%
- Average purity gap: 5.8 percentage points
Most Common Types of Impurities Detected
Based on our LC-MS and HPLC analysis of 1,200+ samples, these are the most frequently identified impurity types:
1. Truncated Sequences (Found in 47% of Impure Samples)
Truncated peptide sequences, where synthesis terminates prematurely, are the most common impurity. These fragments share similar chromatographic properties to the target peptide, making them easy to miss without proper analytical methods.
2. Oxidation Products (Found in 34% of Impure Samples)
Methionine and tryptophan oxidation is the second most common issue. This often indicates poor handling, improper storage, or degradation during shipping rather than synthesis quality issues.
3. Deletion Sequences (Found in 28% of Impure Samples)
Deletion peptides, missing one or more amino acids, are particularly concerning because they may retain partial biological activity but with unpredictable effects.
4. Residual Solvents (Found in 22% of Impure Samples)
TFA (trifluoroacetic acid), acetonitrile, and DMF residues above ICH Q3C limits indicate insufficient purification. We detect residual solvents using GC-MS analysis.
5. Heavy Metal Contamination (Found in 17% of Samples)
Lead, cadmium, and mercury at detectable levels above USP limits. Detected via ICP-MS with sub-ppb sensitivity.
COA Accuracy: The Data
Our comparison of supplier-provided COAs against our independent results reveals:
| Accuracy Category | Percentage | Description |
|---|---|---|
| Exact match (within 2%) | 27% | COA purity matches our results |
| Minor discrepancy (2-5%) | 22% | Slightly inflated but acceptable |
| Moderate discrepancy (5-10%) | 21% | Significant overstatement of purity |
| Major discrepancy (10-20%) | 19% | Seriously misleading COA |
| Critical discrepancy (>20%) | 11% | COA bears no resemblance to actual purity |
