Verify

What analytical testing actually proves

A certificate of analysis is a record of specific tests run on a specific batch on a specific day. It is not a safety assessment, a quality guarantee, or evidence that a compound does anything. Understanding the difference is most of the value.

This page explains laboratory methods. It is not guidance on using any compound in humans, and it does not certify any supplier, laboratory or product.

Identity versus purity

Identity asks: is this the right molecule?

Answered by mass spectrometry, and properly by sequencing work. This is the question most certificates answer least well.

Purity asks: how much of it is something else?

Answered by chromatography, as a percentage of detected peak area. High purity of an unidentified substance tells you nothing useful.

The two are independent. Both are needed, and neither says anything about sterility, endotoxin load, or how the material behaves in a living system.

The common methods

RP-HPLC (reversed-phase high performance liquid chromatography)

What it answers: How much of the material is the main peak, expressed as a percentage of total peak area.

What it does not: It measures relative area, not absolute quantity, and it cannot tell you what the main peak is. A 99% pure sample of the wrong molecule still reads 99%.

LC-MS or MALDI-TOF mass spectrometry

What it answers: The molecular mass of the material, which is the primary evidence of identity.

What it does not: Mass alone cannot distinguish molecules of identical mass, and it does not resolve sequence order without fragmentation work (MS/MS).

Amino acid analysis or peptide content / assay

What it answers: How much actual peptide is in the vial, as opposed to counter-ions, residual water and salts.

What it does not: Frequently missing from vendor certificates. Without it, a labelled 10 mg vial may hold noticeably less peptide.

Water content (Karl Fischer) and residual solvents

What it answers: Leftover water and synthesis solvents such as acetonitrile or TFA.

What it does not: Rarely reported outside pharmaceutical supply chains, and it affects both mass and stability.

Bacterial endotoxin test (LAL)

What it answers: Endotoxin load, reported in endotoxin units.

What it does not: Only meaningful for material intended to be sterile and aqueous. It does not test for viable organisms.

Sterility testing

What it answers: Whether viable organisms grow from the sample under defined conditions.

What it does not: Requires a validated sampling plan. A sterility statement without a method, incubation period and sample size is a claim, not a result.

Reading a certificate of analysis

Work through these fields in order. Anything missing is a question to ask, not a defect to assume.

Product name and catalogue code: Must match the vial label exactly, including any salt form.
Lot or batch number: The link between the document and the physical vial. A certificate with no lot number cannot be tied to anything.
Manufacture and test dates: A certificate tested long before the material was filled describes a different point in time.
Testing laboratory: In-house or third party. Both exist legitimately; only one is independent.
Method for each result: Purity by RP-HPLC, identity by MS, and so on. A number without a method is not a result.
Stated purity and specification: The measured value and the limit it was judged against.
Mass found versus mass expected: The core identity check. These should agree within the instrument's tolerance.
Appearance, water content, counter-ion: Affects what fraction of the vial's weight is actually peptide.
Signature and date: Names the person accountable for the document.

What a certificate can never tell you

That the document belongs to the vial in your hand. Only the lot number links them, and lot numbers can be reused or copied.
That the batch tested is the batch shipped. Retesting on receipt is the only way to know.
That the compound is safe or effective in a person. No analytical method addresses that question.
That the testing laboratory is accredited, unless the accreditation body and scope are named.