HPLC Basics

Posted on June 7, 2026

Understanding the purity and identity testing behind your peptides

When you order a peptide, the number that matters most — its purity — comes from HPLC. This page explains what that means, how the testing works, and how to read the report that comes with your peptide.

What is HPLC?

HPLC stands for High-Performance Liquid Chromatography. It’s the standard laboratory technique for analyzing what’s inside a peptide sample.

A synthesized peptide is rarely 100% the target sequence. Alongside the peptide you ordered, the batch can contain small amounts of related byproducts left over from synthesis. HPLC pulls these apart so each one can be seen, measured, and reported — telling you both how pure your peptide is and helping confirm it’s the right peptide.

How it works

A small amount of dissolved peptide makes a short, one-way trip through the instrument. Four things happen along the way:

1. Inject — A tiny, precise amount of the dissolved sample is injected into a fast-flowing stream of solvent, driven by a high-pressure pump.

2. Separate — The stream carries the sample through a column packed with fine material. The target peptide and each impurity stick to the packing a little differently, so they travel at different speeds and pull apart.

3. Detect — As each component leaves the column, a detector senses it — for peptides, usually by measuring how strongly it absorbs UV light.

4. Read — The detector’s signal is plotted as a chromatogram: a flat line with peaks. Each peak is a separated component. The large central peak is your peptide; smaller peaks are impurities.

What HPLC tells you about a peptide

HPLC answers two different questions, and it’s worth keeping them separate:

Purity — how much of the sample is your peptide. This is the percentage figure on your Certificate of Analysis (COA). HPLC measures it by comparing the size of the main peak to all the peaks combined.

Identity — whether it’s the peptide you ordered. HPLC alone shows how pure a sample is, but not what the main peak is. To confirm identity, the HPLC is usually paired with a mass spectrometer (LC-MS or HPLC-MS), which measures the molecular weight of the peptide and checks it against the expected value.

A complete COA typically includes both: an HPLC chromatogram for purity and a mass spec result for identity.

How to read your HPLC report

A peptide chromatogram is a graph of detector signal (vertical) against time (horizontal). Reading it comes down to a few ideas:

The main peak is your target peptide — usually the tallest and largest.

Smaller peaks are impurities: related sequences and byproducts left from synthesis.

Retention time is how far along the horizontal axis a peak appears — how long that component took to travel through the column. Under fixed conditions it’s consistent, which helps with comparison.

% purity is the area of the main peak as a percentage of the total area of all peaks. So “98% purity” means the main peptide accounts for 98% of everything the detector saw, with impurities making up the remaining 2%.

Reversed-phase HPLC: the standard for peptides

Most peptides are analyzed by reversed-phase HPLC (RP-HPLC). The column packing is non-polar, and the solvent is typically a water/acetonitrile mixture. Peptides separate based on how “water-loving” or “water-repelling” they are, which makes RP-HPLC excellent at resolving a target peptide from closely related impurities. UV detection is commonly done around 214 nm, the wavelength where the peptide’s backbone bonds absorb strongly.

Why purity matters for your work

Impurities aren’t just a number on a page — they can affect results. In research, consistent purity supports reproducible experiments, and very similar impurity sequences can sometimes behave differently from the target in an assay. The right purity level depends on your application: more demanding or sensitive uses generally call for higher purity, while some applications tolerate more. Your own protocol or supplier guidance is the best reference for what you need.

Frequently asked questions

What does the % purity on my COA mean? It’s the proportion of the sample that is your target peptide, measured by HPLC as the main peak’s area divided by the total area of all peaks. 98% purity means 98% of the detected material is the peptide you ordered.

How is peptide purity actually measured? By HPLC. The instrument separates the components, and software calculates each peak’s area. The main peak’s share of the total area is reported as the purity percentage.

What’s the difference between purity and identity? Purity (from HPLC) is how much of the sample is the main component. Identity (usually from mass spectrometry) confirms what that main component is. You want both.

Why does my chromatogram show more than one peak? Because peptide synthesis produces small amounts of related byproducts alongside the target. Each shows up as its own peak. A few small peaks next to a large main peak is normal; the purity figure quantifies how small they are overall.

What kinds of impurities are common in peptides? Typically synthesis byproducts such as sequences missing a residue (deletion sequences) or shortened chains (truncated sequences), plus residues from the synthesis and purification process. These are exactly what HPLC is good at separating out and measuring.

What’s the difference between HPLC and HPLC-MS? HPLC separates the components and tells you purity. HPLC-MS adds a mass spectrometer after the separation, so it also measures molecular weight — confirming the peptide’s identity at the same time.

Why is UV detection done at 214 nm for peptides? The peptide bonds that link amino acids absorb UV light strongly near that wavelength, so 214 nm is a sensitive, general way to detect peptides — including those without other strongly absorbing groups.

Does higher purity always mean “better”? Higher purity is generally preferable, but the right level depends on your application. The most demanding or sensitive uses call for higher purity; others don’t require it. Match the purity to what your work actually needs.

How long does an HPLC analysis take? A single run usually takes from a few minutes up to about an hour, depending on the method and sample. Preparation and review add to the overall turnaround.

References & Standards

The information on this page reflects established analytical chemistry methods and recognized Canadian drug-quality standards.

Methodology — HPLC and peptide analysis

Snyder, L. R., Kirkland, J. J., & Dolan, J. W. (2010). Introduction to Modern Liquid Chromatography (3rd ed.). John Wiley & Sons.

Aguilar, M.-I., & Hearn, M. T. W. (1996). High-resolution reversed-phase high-performance liquid chromatography of peptides and proteins. Methods in Enzymology, 270, 3–26.

Mant, C. T., & Hodges, R. S. (1996). Analysis of peptides by high-performance liquid chromatography. Methods in Enzymology, 271, 3–50.

Aguilar, M.-I. (Ed.). (2004). HPLC of Peptides and Proteins: Methods and Protocols (Methods in Molecular Biology, Vol. 251). Humana Press.

Standards — Canadian and international

Food and Drugs Act, RSC 1985, c. F-27 (including Schedule B, recognized pharmacopoeias). Government of Canada. https://laws-lois.justice.gc.ca/eng/acts/f-27/ https://laws-lois.justice.gc.ca/eng/acts/f-27/

Food and Drug Regulations, CRC, c. 870. Government of Canada. https://laws-lois.justice.gc.ca/eng/regulations/C.R.C.,_c._870/ https://laws-lois.justice.gc.ca/eng/regulations/C.R.C.,_c._870/

International Council for Harmonisation (ICH). Q3A(R2) and Q3B(R2), Impurities in New Drug Substances / Products; Q6A, Specifications: Test Procedures and Acceptance Criteria (adopted by Health Canada).European Pharmacopoeia (current edition), general chapter 2.2.29, Liquid Chromatography (recognized under Schedule B of the Food and Drugs Act).

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