HPLC in One Sentence
High-Performance Liquid Chromatography (HPLC) is an analytical method that separates, identifies, and quantifies the components in a mixture — and for peptides, its primary job is answering one question: what percentage of this sample is actually the peptide it claims to be?
How It Works
The basic principle is separation by differential interaction:
- The sample is dissolved and injected into a stream of liquid solvent (the "mobile phase")
- This stream passes through a column packed with a solid material (the "stationary phase") — typically C18-bonded silica for peptide analysis
- Different molecules interact differently with the stationary phase. Some stick more, some less. This causes them to travel through the column at different speeds.
- A detector at the end (usually UV at 214nm or 220nm for peptides) records when each component exits the column
- The result is a chromatogram — a graph of detector signal over time, where each separated component appears as a peak
Reading the Chromatogram
The chromatogram is the core output of HPLC analysis. For peptide purity assessment:
- The main peak represents your target peptide. Its area relative to the total area of all peaks gives the purity percentage.
- Smaller peaks represent impurities — these could be truncated sequences (peptides missing amino acids), deletion sequences, oxidized forms, or other synthesis byproducts.
- The baseline should be flat and stable. A noisy or drifting baseline can indicate column degradation, solvent contamination, or other analytical issues.
A 99% purity means that 99% of the total peak area is the target peptide, and 1% is everything else combined.
Why HPLC Matters for Research Peptides
Peptide synthesis is an imperfect process. Even the best synthesis produces some proportion of incomplete, modified, or incorrect sequences. HPLC serves two critical functions:
- Purification — preparative HPLC is used during manufacturing to separate the target peptide from synthesis byproducts, achieving high purity
- Analysis — analytical HPLC is then used to measure the purity of the final product, producing the data reported on a Certificate of Analysis
Without HPLC data, there is no objective way to verify what is actually in a vial. A vendor claiming "99% purity" without providing HPLC chromatogram data is asking you to take their word for it.
HPLC vs. Mass Spectrometry
HPLC and mass spectrometry (MS) answer different questions and are complementary:
- HPLC answers: "How pure is this sample?" — it tells you the proportion of the target compound versus impurities
- MS answers: "What is this compound?" — it measures molecular weight, confirming the identity of the peptide
A thorough Certificate of Analysis includes both: MS confirming identity and HPLC confirming purity. See our guide to reading a COA for details on interpreting both.
What to Look For in HPLC Data
When reviewing a vendor's HPLC results:
- The chromatogram should be included — not just a purity number. The graph is the evidence.
- Single sharp peak indicates high purity
- Method details should be stated — column type, solvent gradient, detection wavelength. These details allow the analysis to be replicated.
- Retention time should be reasonable — for C18 reversed-phase HPLC of peptides, retention times typically fall between 10-30 minutes depending on the method
At AminoAxis, every tested batch includes HPLC chromatogram data in our published Certificates of Analysis.
