Why Batch-Level Testing Matters

A report on a peptide describes one batch of it. That sounds like a technicality, but it decides what the report can tell you. This guide explains why testing is tied to a batch, and what follows from that.

Each batch is its own material

A batch is material made together and expected to be uniform within limits; see Understanding Batch & Lot Numbers. Two batches of the same compound are made at different times, often from different lots of starting materials, and can differ in their impurities, their content and their water. A report on one says nothing certain about another.

What a sample represents

A laboratory tests a sample, not the whole batch. The sample stands for the batch only if the batch is uniform and the sample is taken properly. Analytical chemists regard sampling as a source of uncertainty in its own right, alongside the uncertainty of the measurement itself.

Why a product-level claim is weaker

A statement that a compound tests at a given purity invites the reader to assume it holds for all material sold under that name. It can only hold for the batches that were actually tested. A batch-level report makes a narrower and checkable claim: this material, with this number, tested this way, on this date.

Dates belong with the figure

A report describes a sample as of the date it was tested. It records what was measured then, under the conditions of that analysis, and says nothing about the material at a later date.

What batch-level documentation lets you check

• That the batch number on a vial matches a report.
• That the report covers the same product, form and vial size.
• What was tested, by which method, and what was found.
• When the analysis was done.
• Which laboratory issued the report, and whether it can be confirmed with that laboratory.

What it cannot tell you

A report on one batch establishes nothing about a batch that was not tested, and it says nothing about tests it does not list. A missing test is not a pass. How to Read a Certificate of Analysis sets out what the reports on this site do and do not cover.

Where this site fits

Where a batch report is published, it is filed under its batch in the COA Library, so a report always corresponds to a specific production run and its own testing date. Products without a published report say so on the product page rather than showing a placeholder figure. How the reports are produced and shown is described on Testing & quality.

Sources and references

• Eurachem, EUROLAB, CITAC, Nordtest and the RSC Analytical Methods Committee, Measurement Uncertainty Arising from Sampling: A Guide to Methods and Approaches. Eurachem, 2007.
• Eurachem and CITAC, Quantifying Uncertainty in Analytical Measurement, 3rd edition. Eurachem, 2012.
• ICH Q6A, Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products: Chemical Substances. International Council for Harmonisation, 1999. Cited for its definitions; its scope is chemical drug substances.
• 21 CFR 210.3, Definitions. U.S. Code of Federal Regulations, for the terms batch and lot.

Research use

All materials on this site are supplied for laboratory research use only. They are not for human or veterinary use, and this guide gives no instructions for preparing or using them.