What Do Purity Percentage and Chromatogram Peaks Tell You on a COA?

A lab report full of numbers and a jagged line graph can look intimidating the first time you open one. Yet most of the useful information sits in just a few places. Once you know where to look, a single page can tell you how clean a sample was, what it contained, and when it was tested.

Learning to read peptide certificates of analysis COA documents takes about ten minutes of practice and pays off every time you order. This guide explains purity percentages, chromatogram peaks, identity checks, and the details people often overlook, using the reports listed on the Midwest Peps Analysis page as examples.

What a COA Is Meant to Prove

A certificate of analysis is a document from a laboratory that reports what it measured in a specific sample. For a peptide, that usually means purity, identity, and sometimes the quantity of material in the vial.

The value of the document depends on who produced it. A report from an independent laboratory carries more weight than one written by the seller, because the lab has no stake in the sale.

Midwest Peps lists reports from independent labs such as Janoshik and Chromate on its Analysis page. The reports are sorted by series, so you can find the one that matches the product you plan to buy.

Reading the Purity Percentage

The purity figure is usually the first number people look at. It comes from a technique called high-performance liquid chromatography, often shortened to HPLC, which separates the components of a sample and measures each one.

What the number tells you

• It shows the share of the detected signal that belongs to the main compound.

• It is usually calculated as the area of the main peak divided by the total area of all peaks.

• A higher figure means fewer detectable impurities in that sample.

What the number does not tell you

• It does not confirm that the main peak is the correct compound, which is a separate check.

• It does not state how much peptide is in the vial by weight.

• It does not guarantee that every other batch will give the same result.

Treat purity as one piece of evidence, not the whole story. A strong report combines purity with identity data, a clear date, and a way to verify the document.

How to Read the Chromatogram

The chromatogram is the line graph on the report, and it shows how the sample moved through the instrument. Each peak represents a component, and the taller or wider the peak, the more of that component was detected.

Parts of the graph

• The horizontal axis shows retention time, which is how long each component took to pass through the column.

• The vertical axis shows the detector response, which reflects how much of each component was seen.

• The tall main peak is the compound of interest.

• Smaller peaks nearby are impurities or related substances.

• The baseline is the flat line between peaks, and a clean, steady baseline suggests a well-run test.

When you look at a chromatogram, check that one dominant peak holds most of the area. Several large peaks of similar size would suggest a mixture, even if a headline number looks acceptable.

Also check that the graph belongs to the same sample as the rest of the report. The sample name, date, and any task or batch number should match across the page.

Identity and Quantity Checks

Purity alone cannot tell you that a vial contains the right compound. Identity is usually confirmed with mass spectrometry, which measures the molecular mass and compares it with the expected value.

Some reports also list a quantity, such as milligrams per vial. That number is separate from purity, because a sample can be highly pure and still contain less peptide than the label suggests due to water and counter-ions in the powder.

If a report shows only purity and no identity or quantity data, ask the supplier whether more documentation exists. A missing piece is not always a problem, but it is worth a question.

Making Sure the Report Fits Your Product

A good report is useless if it belongs to a different product. Compare the sample name and strength on the document with the exact item you plan to order, since similar names can hide different sizes.

The Analysis page groups reports under labels such as the R series, T series, Glow, and Klow, along with a list of additional products. The numbers in those labels often line up with catalog sizes, but the site does not state the mapping, so confirm it with the supplier before relying on it.

Where a report offers a verification link, open it and compare the details with the document. A live record from the laboratory is stronger evidence than an image alone.

Keeping Your Own COA Log

Labs that buy research peptides regularly benefit from a simple record of every report they receive. A spreadsheet with the product, strength, lab, test date, purity, and a link or file name is enough to begin with.

A log makes it easy to spot changes from one purchase to the next. It also gives you something to point to later if a result in your own work looks unusual and you need to rule out a change in material.

Red Flags to Watch For

• A report with no named laboratory or no way to verify it.

• A purity figure that appears with no chromatogram at all.

• A sample name or strength that differs from the product being sold.

• A test date that is very old or missing completely.

• A report that looks identical across clearly different products.

None of these automatically means a seller is dishonest, but each one justifies a direct question before you order. Clear answers are a good sign, and vague ones are worth noting.

Why Researchers Choose Midwest Peps

Midwest Peps is a Midwest-based chemical supplier of high-purity research peptides and biochemicals, and it publishes its independent test reports on a dedicated Analysis page. Reports are organized by series, linked to outside laboratories, and updated regularly, with a standing invitation to request any document that is not listed. Orders placed before noon ET Monday through Saturday typically ship the same business day, and every product is sold for laboratory research only.

FAQs

Q1: What is a good purity percentage on a COA?
Higher is better, but the figure should be read alongside the chromatogram, identity data, and test date rather than on its own.

Q2: What do the peaks on a chromatogram represent?
Each peak represents a component of the sample, and the tallest peak is normally the main compound while smaller peaks are impurities.

Q3: Is purity the same as the amount in the vial?
No, purity describes the share of detected signal, while quantity describes how much peptide is present by weight.

Q4: How can I tell a report is genuine?
Look for a named independent laboratory, matching sample details, a clear date, and a verification link you can open and compare.

Q5: What should I do if the report does not match my product?
Contact the supplier before ordering and ask for the correct document, since the Analysis page says missing reports will be provided on request.

Where should I keep the test report?
Store it with your receiving notes and inventory log so each vial can be traced to its documentation.

Can I store reconstitution solution next to the dry peptide?
 Keep it separate and clearly labeled, so that supplies are never confused with the dry material.