When shopping for research peptides, you will frequently see purity listed as a percentage — 95%, 98%, 99%, or even higher. But what does this number actually mean for your dosage calculations? Understanding peptide purity is essential for accurate dosing and getting the results you expect from your research protocol.
What Peptide Purity Actually Measures
Peptide purity, typically measured via High-Performance Liquid Chromatography (HPLC), indicates what percentage of the total material in the vial is the intended peptide sequence. The remaining percentage consists of impurities — truncated sequences, deletion sequences, oxidized forms, or other synthesis byproducts.
For example, a 5mg vial labeled at 98% purity contains approximately:
- 4.9mg of the target peptide
- 0.1mg of impurities (incomplete sequences, salts, etc.)
How Purity Affects Your Effective Dose
| Labeled Amount | 95% Purity | 98% Purity | 99% Purity |
|---|---|---|---|
| 5mg vial | 4.75mg active | 4.90mg active | 4.95mg active |
| 10mg vial | 9.50mg active | 9.80mg active | 9.90mg active |
| 250mcg dose | 237.5mcg actual | 245mcg actual | 247.5mcg actual |
| 500mcg dose | 475mcg actual | 490mcg actual | 495mcg actual |
Does the Difference Actually Matter?
For most practical purposes, the difference between 98% and 99% purity is negligible — about 1% of your dose. However, the gap between 95% and 99% purity is more significant:
- At 95% purity: You are effectively underdosing by 5% compared to what you calculated. Over a multi-week protocol, this adds up.
- The impurity concern: Lower purity doesn't just mean less peptide — it also means more impurities. These can include truncated peptide sequences that may have unpredictable biological activity, or synthesis byproducts that could cause injection site reactions.
- Batch-to-batch consistency: Higher purity peptides tend to have more consistent effects between vials, because less of the product is variable impurities.
Should You Adjust Your Dose for Purity?
At 98%+ purity, most researchers do not adjust their dose calculations. The 1-2% difference falls within the normal margin of measurement error in reconstitution and drawing. However, if you are using peptides at 95% purity or below, consider calculating your dose based on the actual active content:
Adjusted dose = Desired dose ÷ (Purity % / 100)
Example: You want 500mcg of active BPC-157, but your vial is 95% pure:
500 ÷ 0.95 = 526mcg (draw enough for 526mcg to get 500mcg of active peptide)
Purity Grades and What They Mean
| Purity Range | Grade | Typical Use | Dosing Adjustment Needed? |
|---|---|---|---|
| 99%+ | Pharmaceutical grade | Clinical research, highest accuracy | No |
| 98-99% | Research grade (high) | Standard research protocols | No |
| 95-98% | Research grade (standard) | General research | Minor — optional |
| Below 95% | Crude / low grade | Not recommended for injection research | Yes, and reconsider supplier |
How to Verify Purity Claims
- Request the COA (Certificate of Analysis): Any reputable supplier provides HPLC data showing the purity peak. The main peak should dominate the chromatogram.
- Check for third-party testing: The most reliable purity data comes from independent labs, not the manufacturer's own testing.
- Look at the HPLC chromatogram: A single tall, sharp peak indicates high purity. Multiple peaks or a broad main peak suggests impurities.
- Mass spectrometry (MS) confirmation: HPLC tells you purity; MS confirms identity. Both should be on a quality COA.
Key Takeaways
- Peptide purity directly affects how much active compound you're actually dosing
- At 98%+ purity, no dose adjustment is needed for practical purposes
- Below 95% purity, you should adjust dosing and question your supplier
- Always verify purity claims by reviewing the COA and HPLC data
- Higher purity means fewer impurities and more consistent results
Does peptide purity decrease after reconstitution?
The purity percentage itself does not change after reconstitution, but the peptide can degrade over time in solution. Degradation is different from impurity — it means the active peptide is breaking down. Proper storage (refrigerated, protected from light) minimizes degradation.
Is 98% purity good enough for research?
Yes. 98% purity is considered high-quality research grade and is the standard for most peptide research protocols. The 2% impurity is unlikely to affect your results in any meaningful way.