How to read a peptide certificate of analysis

A certificate of analysis (COA) is the laboratory report for one batch of material. It is the difference between taking a supplier’s word and checking it. Many readers look at the purity figure and stop, which is how a weak certificate gets past them.

This guide goes through the sections of a peptide COA, what each test shows, and what to look for before you rely on one.

What a certificate is, and what it is not

A COA records the results of tests run on a specific production lot. A useful one names the lot, carries a date and comes from an analytical laboratory. It is evidence about that lot, not a description of a product line.

It is not a statement that a material is suitable for any use outside the laboratory. A certificate reports identity, purity and contamination results; it says nothing about use in people or animals.

The results that matter

A strong certificate reports more than purity. Read these together:

• Purity (HPLC). High-performance liquid chromatography reports how much of the sample is the target peptide compared with related impurities. Look for a stated percentage and the method used.
• Identity (mass spectrometry). Confirms the measured mass matches the intended peptide. A purity figure means little if the molecule is the wrong one.
• Net peptide content. The actual amount of peptide, as opposed to water and counter-ions. Vials with the same label can differ here, and it changes every concentration you calculate.
• Sterility. Screens the finished product for microbial contamination.
• Bacterial endotoxin (LAL). Detects endotoxins, which can interfere with cell-based and other sensitive assays at very low levels.
• Heavy metals. Screens for lead, arsenic, cadmium and mercury carried over from raw materials or synthesis.

Signs to pause

• No lot number, or a lot number that does not match the vial in front of you.
• A single test, usually HPLC. One purity figure says nothing about identity or contamination.
• An old certificate reused across many batches.
• No laboratory named, no date, or no way to check the source.
• Descriptions where there should be numbers and methods.

Match the certificate to the lot

The most useful habit is the simplest: check that the lot number on the certificate matches the lot number on the vial. A certificate for a different lot tells you about a different batch.

At US Prime Peptides the lot number is printed on the vial label and on the packing slip. Send it to us and we will send the certificate for that lot.