How to read a certificate of analysis

A certificate of analysis (COA) is the laboratory's record of what it found when it tested a specific batch. Read properly, it answers two questions: is this the compound it claims to be, and how much of the vial is that compound. Read casually, it is a page with a big number on it. This guide is about reading it properly.

First, check it belongs to your vial

Before any result, match three things between the COA and the label:

• Compound name and sequence. The peptide should be named and, ideally, its amino-acid sequence given.
• Batch or lot number. This is the link between the paper and the glass. A COA without a batch number, or with one that does not match, tells you nothing about your vial.
• Date of analysis. Results should post-date manufacture and pre-date sale.

HPLC purity

High-performance liquid chromatography separates the contents of a sample by how they interact with a column. The output is a chromatogram: a line with peaks. The main peak is your peptide; everything else is something that is not your peptide.

Purity is the area of the main peak as a percentage of all peak area. A result of 99.2% means that of everything the detector saw, 99.2% was the target compound.

What to look for:

• The chromatogram itself, not just the number. A single sharp peak with a flat baseline is what you want. Several substantial peaks, or a broad hump, are worth asking about even if the headline number is high.
• The method. Column type, gradient and wavelength should be stated. Different methods can give different figures for the same sample.
• Consistency. If a supplier's every batch is exactly 99.9%, be sceptical. Real results vary a little.

Mass spectrometry identity

HPLC tells you how pure something is, but not what it is. Mass spectrometry does that: it measures the molecular weight of the main peak and compares it with the calculated weight of the peptide sequence.

Look for the observed mass and the theoretical mass side by side. They should agree to within a fraction of a dalton for a small peptide. A close match confirms the peak in the HPLC really is the compound named on the label, and not something with a similar retention time.

Endotoxin and water content

Two further tests appear on a thorough COA:

• Endotoxin (LAL test). Reported in endotoxin units per milligram. Lower is better; a stated limit and a result under it is what you want to see.
• Water content or net peptide content. Lyophilised peptides carry some bound water and counter-ions. Net peptide content tells you what fraction of the powder mass is actually peptide, which matters when you are calculating concentration.

Red flags

• No batch number, or a batch number that does not appear on the vial.
• A purity figure with no chromatogram.
• A COA issued by the manufacturer only, with no independent laboratory named.
• Results that are identical across every batch and every compound.
• A certificate that names a different compound, sequence or quantity from the one you bought.

How we do it

Each batch we list goes to an independent Australian laboratory for HPLC purity and LC-MS identity before it is offered for sale. The batch number is printed on every vial, and the result is on file against it. If you want the certificate for a batch you have bought, send us the batch number and we will send the document.