HPLC Testing Explained

What is HPLC?

HPLC — High-Performance Liquid Chromatography — is an analytical technique used to separate, identify, and quantify individual components in a mixture. In peptide research, HPLC is the gold standard method for determining purity — the percentage of the target peptide relative to total material in a sample.

When you see a peptide listed as "≥98% purity by HPLC," this means that HPLC analysis confirmed at least 98% of the material in the sample is the intended peptide, with less than 2% consisting of synthesis by-products, truncated sequences, or other impurities.

How HPLC Works

The Basic Process

1. Sample injection: A small volume of the peptide sample (dissolved in an appropriate solvent) is injected into the HPLC system.
2. Separation: The sample is pushed through a packed column (the stationary phase) by a high-pressure liquid solvent (the mobile phase). Different components in the sample interact differently with the column material, causing them to travel at different speeds.
3. Detection: As separated components exit the column, they pass through a UV detector (typically at 214 nm or 220 nm wavelength, which is optimal for detecting peptide bonds). Each component produces a peak in the chromatogram.
4. Analysis: The area under each peak is proportional to the amount of that component. The purity percentage is calculated by dividing the target peptide's peak area by the total peak area.

Reverse-Phase HPLC (RP-HPLC)

The most common HPLC method for peptide analysis is reverse-phase HPLC. In RP-HPLC, the column contains a non-polar stationary phase (typically C18-bonded silica) and the mobile phase is a gradient of water and an organic solvent (usually acetonitrile) with a small amount of acid (TFA or formic acid). Peptides separate based on their hydrophobicity — more hydrophobic peptides elute later.

Understanding Purity Percentages

• ≥99% purity: Pharmaceutical-grade. Used for clinical-grade research and regulatory-submission studies.
• ≥98% purity: Research-grade. The standard for most in-vitro research applications. This is the minimum purity OzTideLab supplies.
• 95-97% purity: Acceptable for preliminary screening studies but may introduce confounding variables in quantitative research.
• <95% purity: Not recommended for research. High impurity content can significantly affect experimental reproducibility.

Reading a Certificate of Analysis

A Certificate of Analysis (CoA) for a peptide typically includes:

• Peptide identity: Name, sequence, and molecular formula
• Molecular weight: Theoretical vs. observed (confirmed by mass spectrometry)
• HPLC purity: The percentage purity from HPLC analysis, including the method used (column type, mobile phase, gradient conditions)
• Appearance: Physical description of the lyophilised product (e.g., "white to off-white powder")
• Batch number: Unique identifier for traceability
• Chromatogram: The actual HPLC trace showing the peaks — the main peak should be dominant with minimal additional peaks

Why Purity Matters for Research

In scientific research, the quality of your reagents directly affects the quality of your results. Using low-purity peptides introduces several risks:

• Confounding variables: Impurities may have their own biological activity, making it impossible to attribute observed effects solely to the target peptide
• Reproducibility issues: Different batches with different impurity profiles will produce inconsistent results
• Inaccurate dose-response curves: If only 90% of your "peptide" is actually the target compound, your effective concentration is 10% lower than calculated
• Publication risk: Reviewers increasingly expect detailed purity documentation for peptide reagents