Read the certificate before you open the carton.

A certificate of analysis describes a single production lot. It is written after the lot has been lyophilized and tested, and it records what the laboratory measured in that material on the day it was tested. It is not a specification, not a promise about the next lot, and not a description of the compound in general. Every figure on it is past tense. Read it that way.

The document is short. A typical certificate for a lyophilized peptide fits on one page: a header naming the compound and the lot, a table of tests with a method, a result and a stated acceptance range for each, and a release line. The order of the blocks varies between laboratories, but the blocks themselves do not. The sections below take them in the order a buyer should check them.

Start at the top. The compound name should be the name on your order line, and where the certificate lists a CAS number it should agree with the one on the product page. The lot number is the key to everything else: it is the string that will appear on every vial label from this batch. Copy it into your receiving record now, because the match you make on the dock later depends on it.

The date matters more than most buyers expect. A certificate carries a test date, sometimes a separate release date, and together they tell you when the measurements were made. A lot tested this quarter and a lot tested two years ago can both be genuine, but the older certificate describes older material. If the date looks stale against the ship date on your quote, ask whether a newer lot is being assigned before the order is confirmed.

Mass spectrometry measures the molecular mass of the material and compares it to the mass expected for the named compound. That is all this guide says about the method. What you read on the certificate is a measured value, an expected value and a pass line saying they agree within the instrument's tolerance. If the expected value is printed, check it against the molecular weight on the product page and the PubChem entry it links to; if the three disagree, ask before you accept the lot.

Identity comes first because purity without identity is meaningless. A chromatogram can show one clean peak and still be the wrong molecule, or the right sequence with a missing modification. The identity line is what ties the purity figure to the compound on your purchase order. If a certificate has a purity result and no identity result, it is incomplete, and the correct response is to request the full document rather than to read the half you have.

High-performance liquid chromatography separates the dissolved sample into its components and reports the main peak as a share of the total. That is the method in one sentence. On the certificate you will see the figure, the method conditions in a line or two, and sometimes the chromatogram itself. This guide does not quote a purity figure, and neither does any page on this site, because the figure belongs to a lot, not to a catalog.

Read the purity line as a statement about the past: this lot, that day, that column. It is not a forward guarantee, it does not describe the lot that follows, and it says nothing about how much material is in the vial. Fill weight is a separate question, answered by the fill line on the order, not by the chromatogram. A buyer who reads the purity figure as the whole certificate has skipped the two lines that give it meaning.

The appearance line is the one you can verify without an instrument. It states what the laboratory saw when it opened a vial from the lot: usually a white to off-white lyophilized powder or cake. Hold one of your vials against a plain background and compare. A yellow tint, a glassy film instead of a cake, or visible moisture is not a laboratory question; it is a reason to photograph the vial and email the desk before opening any more of the shipment.

The endotoxin line reports the result of a bacterial endotoxin test on the lyophilized material, with the method and the unit stated beside it. It is a separate measurement from purity and from identity, and a lot can pass both of those and still carry endotoxin. Note the unit, the result and the limit applied. What an endotoxin result is not is a sterility statement; nothing on this catalog is sterile-filled, and the certificate does not say otherwise.

Certificates on this catalog are lot-specific and available on request. That phrase means two things. The document exists for every lot that ships, and it is sent when you ask for it, before the order or after. It does not mean a certificate is folded into every carton, and it does not mean one certificate stands for every lot of a compound. The right time to ask is while you are quoting, so the certificate and the quote refer to the same lot.

To ask, use the COA request page or reply to your quote email. Name the compound, the fill weight and, if you have it, the lot number. If the lot is not yet assigned, ask for the current lot and ask again at dispatch if the lot changes. A safety data sheet is requested the same way. Keep the certificate with the purchase order rather than in a general documents folder; the two are read together.

Three checks, in this order. First, the lot number: read it from a vial label, not from the carton, and compare it character by character to the header of the certificate. Second, the crimp: the aluminium collar over the stopper should be tight, unmarked and flush, with no lifted edge. Third, the cake: a whole disc sitting at the bottom of the vial, not a shrunken lump, a smear up the glass or loose powder that moves when the vial is tilted.

Do this on a sample of vials from each carton, and on every vial if the shipment is small. A mismatch on the lot number means the document in your hand describes different material; stop and ask for the right certificate before the vials go into storage. A failed crimp or a collapsed cake is a receiving problem for that vial, not a laboratory problem for the lot, and it is easier to resolve on the day the carton arrives than a month later.