How to read a peptide certificate of analysis

The first time most people open a peptide COA, the eye goes straight to the purity figure and stops there. That figure matters, but it is one line on a page that usually has five or six sections, and most of the useful information is elsewhere. This page reads a report the way a QC reviewer would, from the top down.

(Checking whether a report is genuine, and whether it belongs to the vial on the bench, is a separate job. This page is about understanding what the report says.)

1. The header: who wrote this

The top of the page should name the laboratory, give an address, and carry a report, task or certificate number. Note the number. It is how the lab finds its own copy later.

If the header shows only the supplier's logo and no lab name, the rest of the page should be read without knowing who did the analysis.

2. The sample block: what was tested

This block describes what arrived at the lab. Look for:

• Sample or product name, as the supplier submitted it
• Lot or batch code
• Stated amount, for example 10 mg per vial
• Date received and date analyzed
• Sometimes a sample description, such as "white lyophilized powder"

The lot code here is the most important line on the page. Everything below it applies only to that lot.

3. The test table: what was measured

Most COAs print a table with four or five columns:

Column	What it means
Test	The question being asked, such as purity, identity or endotoxin
Method	How it was measured, such as HPLC-UV at 214 nm, ESI-MS, or kinetic chromogenic LAL
Specification	The limit the lot had to meet, such as "98.0% or higher" or "conforms"
Measured value	What the lab found, such as 99.32% or 3,307.6 Da
Status	Pass, fail, or conforms, when the lab includes it

Read across each row. A measured value means little without its method next to it, because the same lot can read differently under different conditions.

Watch the units. Purity is usually an area percent. Identity is usually a mass in daltons or an m/z value. Endotoxin can be EU/mg, EU/mL or EU per vial, and those are not interchangeable without knowing how the sample was prepared for the assay.

4. The chromatogram: where the purity figure came from

If the report includes HPLC, there should be a chart: time across the bottom, detector signal up the side, a large main peak, and usually a few small ones. Under it, a peak table lists each peak's retention time, area and area percent. The purity figure is the main peak's area percent from that table.

A full report shows baseline at both ends of the run and labeled axes. A cropped chart with no axes or no peak table is harder to interpret, and it is reasonable to ask for the complete page.

5. The mass spectrum: what the main peak is

HPLC says how much of the sample sits in one peak. Mass spectrometry says what that peak is. The spectrum shows signal against m/z, and the report states an observed mass beside the expected (theoretical) mass. Small differences inside the instrument's stated tolerance are normal. A large mismatch is not.

6. Extra panels

Some lots carry more tests: peptide content, endotoxin, microbial counts, elemental impurities, residual TFA, water content. Each one answers its own question and has its own units. A pass on one says nothing about the others. If a test is absent, the report has no data for it.

7. The approval line and the fine print

At the bottom: the analyst or approver, a date, and often a statement about scope, such as "test results relate only to the sample received." That sentence is not boilerplate to skip. It means the lab is vouching for the sample it received and nothing else.

A short reading order

1. Lab name and report number
2. Lot code and dates
3. Every row of the test table, with its method
4. The chromatogram and peak table
5. The mass spectrum and the mass match
6. Any extra panels
7. Approval line and scope statement