How to Verify Peptide Purity: A Lab Guide

Don’t Guess, Test: A Researcher’s Step-by-Step Protocol for Validating Peptide Purity

Why ≥98% HPLC purity isn’t a suggestion—it’s the baseline for reproducible science. Here’s how to confirm it.

Step 1: Decode the Certificate of Analysis (CoA)

• Demand batch-specific CoAs with 3 elements:

  • HPLC chromatogram: Main peak should comprise ≥98% of total area.

  • Mass spectrometry (MS): Peak must match Retatrutide’s theoretical mass (4731.4 g/mol).

  • Endotoxin levels: <0.25 EU/mg to prevent cell-line contamination.
    Avoid suppliers who provide “representative” CoAs—this is a major red flag.

Step 2: Run In-House Verification Tests

• HPLC Setup:

  • Column: C18 reversed-phase

  • Flow rate: 1.0 mL/min

  • Detection: UV absorbance at 220 nm

• Acceptance criteria: Single symmetrical peak with retention time matching reference standard 2.

• Quick check: Suspect impurities if >2% peaks appear outside 4.5-5.5 min window.

Step 3: Stress-Test Stability

• Protocol: Reconstitute 1mg Retatrutide in bacteriostatic water. Store aliquots at:

  • -20°C (control)

  • +4°C (72 hrs)

  • Room temp (24 hrs)

• Pass benchmark: HPLC purity declines ≤2% under stress conditions 8.

Case Study: How Impurities Skew Research

A 2024 study found truncated peptides in “95% pure” Retatrutide batches acted as GIP antagonists—reversing glucose responses in murine models .

Pro Tip:
Re-test upon arrival! 33% of peptides degrade during transit without lyophilization and temperature-controlled shipping.

Demand CoAs first: Download Retatrutide CoA Template