Reading a Certificate of Analysis

A Certificate of Analysis is a laboratory's written account of what it found when it tested one specific batch of one specific material. It is not a description of the compound in general and it is not a statement about anything the compound does. It is a record of measurements, made on a sample drawn from a numbered lot, on a stated date, by a named laboratory.

Every Dohrna line is supplied with a certificate for its lot. This page explains what each part of that certificate means, so that a laboratory receiving a vial can read the document against the label in front of it.

The header: what was tested

The top of the certificate identifies the material and the test. Five fields matter, and every one of them should agree with the vial label and the product page.

Compound name. The name of the material as the catalogue lists it. A certificate whose name differs from the label — a different compound, a different salt, a different sequence variant — is not a certificate for that vial.

Catalogue number. The line's number in the Dohrna catalogue, printed on the label and on the product page. Two lines with similar names are told apart by this number, not by the name.

Lot number. The batch identifier. This is the field that makes the certificate specific: a certificate is issued for one lot and applies to that lot only. The same compound made on a different day carries a different lot number and a different certificate.

Date of analysis, and the issuing laboratory. When the tests were run and who ran them. The laboratory is identified by name on the certificate itself, together with its accreditation reference where one is held.

Nominal quantity. The mass of material stated to be in the vial, in milligrams, as printed on the label.

Identity: is it the right molecule?

The identity section answers one question — is the material in the vial the compound named on the label? For a peptide this is established by mass spectrometry.

The certificate states the calculated molecular weight (what the named sequence should weigh, derived from its formula) and the observed mass (what the instrument measured). The two should agree within the instrument's stated tolerance, ordinarily a fraction of a dalton. An observed mass that matches the calculated one is the evidence that the sequence is what the label says.

Some certificates also carry an amino-acid analysis or a sequence confirmation line. Where present, these are further identity checks; where absent, mass spectrometry is the identity test.

The calculated molecular weight and the molecular formula for each line are stated on the product page under Specification, so the figure on the certificate can be checked against the figure on the site.

Purity: how much of the material is that molecule?

The purity section is the chromatogram — the trace produced by liquid chromatography (HPLC), the standard analytical method for synthetic peptides.

In a chromatogram, the material is passed through a column that separates it into its components, and a detector records what comes off and when. Each component appears as a peak. The main peak is the compound; smaller peaks are anything else present — shorter or altered sequences left over from synthesis, or by-products of purification.

The purity figure, stated as a percentage, is the area of the main peak divided by the area of all peaks together. A purity of 98% means that 98% of the material the detector saw was the single compound. The percentage refers to peak area, not to mass, and it says nothing about anything the chromatography cannot see — salts, water and counter-ions are not peaks, and are accounted for separately (below).

The certificate should state the method beside the figure: the column, the solvent gradient and the detection wavelength. These details allow another laboratory to repeat the measurement. A purity figure with no method beside it cannot be checked and should be read accordingly.

The chromatogram image itself accompanies the figure. A clean trace shows one dominant peak with a flat baseline. Multiple peaks of similar height, a broad main peak, or a rising baseline are all things a reader should notice, whatever the stated percentage.

Appearance and other physical tests

Appearance records what the analyst saw: usually "white to off-white lyophilised powder" for a peptide. A colour or texture that differs from the certificate is worth a query.

Peptide content (or net peptide content) is the proportion of the vial's mass that is peptide rather than bound water and counter-ion. Lyophilised peptides retain some water and carry a counter-ion from purification — acetate, or trifluoroacetate (TFA), depending on the process. A vial labelled 5 mg with a peptide content of 80% contains about 4 mg of the peptide itself. The certificate states which counter-ion the material carries, and the product page states the salt form under Specification.

Water content and residual solvent lines, where present, quantify what else is in the vial.

What a certificate does not say

A Certificate of Analysis is a statement about a sample of material. It is not a statement about suitability for any purpose, it carries no information about any organism, and it is not a document of approval. The material it describes is supplied for laboratory research use only; a certificate confirms what the material is, and no more.

It also applies to one lot only. A certificate for lot A says nothing about lot B, even of the same compound from the same laboratory. Where the label and the certificate disagree on the lot number, the certificate does not apply.

Where to find the certificate for a Dohrna line

Each product page carries a Certificate of Analysis card. Once a lot is released, the certificate for that lot is published there as an image, with the lot number in the caption. The label on the vial carries the lot number and a scannable code that opens dohrna.com.

If a lot number on a label does not match a certificate on the site, the certificate for that lot can be requested by email to support@dohrna.com, quoting the catalogue number and the lot number. See the companion guide, Verifying a lot.