Certificate of Analysis

Analytical Reference

How to Read Your HPLC Certificate of Analysis

A guide to understanding the chromatogram on your CoA, how purity is calculated from it, and what to check before you trust one.

What a CoA actually is

A Certificate of Analysis is a document issued by a testing laboratory for one specific production batch of a compound. It reports what the lab actually measured — not what the manufacturer claims, and not a generic spec sheet for the compound in general. A CoA that isn't tied to a specific batch number isn't really a CoA; it's marketing copy wearing a lab coat.

Most research peptide CoAs report two things: identity (is this actually the compound it claims to be) and purity (how much of the sample is that compound, versus synthesis byproducts, degradation products, or unrelated impurities). The chromatogram is where the purity figure comes from.

What HPLC is doing

High-Performance Liquid Chromatography separates a sample into its individual components before measuring them. The sample is pushed through a column packed with material that different molecules travel through at different speeds, so a mixture that goes in as one liquid comes out the other end as a series of separated bands, spread out over time. A detector — usually UV absorbance for peptides — measures each band as it exits.

The chromatogram is simply that detector reading, plotted against time. Each component in the sample shows up as its own peak.

Anatomy of the chromatogram

An annotated example of what you're actually looking at.

0 2 4 6 8 10 12 0 100 200 300 Retention Time (minutes) Absorbance (mAU) 6.00 min — target compound 98.7% of total peak area 2.7 min: 0.4% trace impurity 8.6 min: 0.9% trace impurity baseline

Illustrative example. Every real chromatogram looks slightly different — what matters is the shape of the logic, not this specific trace.

How the purity number is calculated

The area under each peak is roughly proportional to how much of that substance passed the detector. Purity by peak area is simply:

area of target peak ÷ total area of all peaks × 100

In the example above, the target compound's peak accounts for 98.7% of the total area under all three peaks — so the CoA would report 98.7% purity. The two small peaks are the synthesis byproducts or degradation products making up the remaining 1.3%. A clean, well-synthesised compound shows one dominant peak and little else; a poorly synthesised or degraded one shows several peaks fighting for area.

Before you trust a CoA, check

Order doesn't matter here — these are independent checks, not steps.

✓
Batch number matches what you received
The lot/batch number printed on the CoA should match the number on the vial or packaging in front of you. A CoA for a different batch tells you nothing about the batch you actually have.
✓
Compound name and reference standard align
The retention time of the main peak should be consistent with the lab's reference standard for that compound, not just labelled correctly in text. Identity and purity are two separate claims — a CoA should support both.
✓
Test date is recent relative to production
Peptides can degrade over time, especially once reconstituted. A CoA dated close to the manufacture date tells you about the compound as made; it says nothing about its condition after months in transit or storage.
✓
Testing lab is named and independent
A third-party lab with no financial stake in the result carries more weight than an in-house test run by the manufacturer itself. Look for a lab name, not just a logo.
✓
The peaks and the printed percentage actually agree
If the document states "99% purity" but the chromatogram shows several substantial peaks sharing the area, the image and the headline number are telling different stories. Trust what the graph shows over what the text claims.

Signs a CoA isn't genuine

  • The identical chromatogram image appears on multiple different products or batch numbers
  • No batch/lot number at all, or one that doesn't correspond to anything on the product itself
  • No named testing laboratory, or a lab name that doesn't appear to exist independently
  • The retention time or peak shape doesn't match what's typical for the stated compound class
  • Visibly re-touched or low-resolution graphics where axis labels look pasted on
  • A purity percentage with no accompanying chromatogram to support it at all

This page explains how to read and evaluate laboratory analytical documentation. It is not guidance on compound use, dosing, or administration. All compounds referenced across this site are supplied for laboratory research use only and are not for human or veterinary use.