Reporting a peptide's source and lot in a methods section

Why reviewers ask about peptide source

Two vials of the same catalogue item from different lots can differ in salt form, purity and peptide content. If a methods section names only the peptide, a reader cannot tell which material was used or repeat the work with comparable material. PLOS ONE's guidelines frame the purpose of Materials and Methods as giving enough detail for suitably skilled investigators to fully replicate the study. [4]

For peptides bought from research-chemical storefronts, this matters even more, because the seller may not be the manufacturer and the certificate may come from a third-party laboratory. The methods section is where that chain becomes visible.

What the guidelines actually ask for

ARRIVE 2.0 groups its 21 items into the Essential 10 and a Recommended Set. [2] Item 9, Experimental procedures, asks authors to describe procedures for each group in enough detail for others to replicate them, and for reagents such as antibodies and chemicals lists manufacturer, supplier, catalogue number, lot number if applicable, purity of the drug if applicable, and RRID. It explains that RRIDs are unique and stable, allowing unambiguous identification of reagents or tools used in a study. [1]

The MDAR framework, published in PNAS in 2021, sets a basic minimum requirement and aspirational best practices for materials, design, analysis and reporting, organised around accessibility, identification and characterisation. [5] PLOS ONE asks for the commercial supplier, catalogue or clone number and, if known, the batch number for antibodies, and the repository or company and catalogue number for cell lines. [4] Peptides are not singled out, but the same three elements carry over: who supplied it, which item, which lot.

RRIDs and synthetic peptides

The RRID initiative lists the resources it identifies as core facilities, instruments, organisms, antibodies, plasmids, cell lines, software tools and databases. The site does not list chemicals or synthetic peptides as covered resource types. [3]

If a peptide has no RRID, write the sequence (with terminal modifications), salt form, supplier, catalogue and lot numbers instead. An antibody raised against the peptide, or a cell line used with it, may well have an RRID and should be cited separately.

Template methods paragraph

Adapt this to the facts in your records. Leave out any claim you cannot document.

[Peptide name] ([sequence, N- and C-terminal modifications], [salt form, e.g. acetate] as stated on the supplier certificate) was obtained from [supplier], [city, country] (catalogue no. [number], lot [number]); the supplier identified the manufacturer as [name] / did not identify the manufacturer. The lot certificate of analysis ([issuing laboratory], report [number], dated [date]) reported [x]% purity by reversed-phase HPLC and an observed mass of [value] Da (theoretical [value] Da). [Independent verification: a retained sample from the same lot was analysed by [laboratory] on [date] by [method], giving [result]. / No independent verification was performed.] Net peptide content was [value, method / not determined]. The material was stored at [temperature] until use; certificates and raw data are available from the authors on request.

Two details reviewers notice: whether purity is the supplier's value or your own, and whether the lot in the methods matches the lot in your records. State both plainly.

Supplier documents to archive with the dataset

Keep originals, not screenshots of product pages, and file them under the lot number so they can be produced if a reviewer, editor or later reader asks.

Common gaps and how to word them honestly

If the supplier sent no lot-specific certificate, do not cite a product-page report as if it described your material. Write that a certificate for the lot was requested and not provided. If purity comes only from the supplier, attribute it: "reported by the supplier" rather than "was 98% pure".

If you switched lots partway through a study, report each lot and which experiments used it. That is more useful to a reader than a single catalogue number that hides the change.

• Supplier, catalogue and lot match your archived records.
• Sequence, modifications and salt form are stated.
• Purity and identity are attributed to the supplier or to your verification.
• No RRID is invented for a resource type that does not have one.
• Lot changes during the study are disclosed.