What a Reviewer Asks About Material Provenance: Where From, How Pure, Which Batch, Who Checked

When a manuscript relies on a purchased compound, the reviewer's questions about it reduce to four: where did it come from, how pure was it, how was that established, and which batch was used. A fifth follows when the answers are thin — who checked it, other than the seller. None of these questions is hostile. They follow from the principle that governs the rest of a methods section: a reader must be able to identify the material, obtain it, and know what it was ^[2].

This article is about anticipating those questions and answering them honestly, including when the material came from a commercial research supplier. The statement itself — what to write in the methods about a compound's source — is covered in this cluster's pillar; here the focus is the exchange with a reviewer, and the documents that have to sit behind it.

The questions that recur

Review is where the checks a journal applies before publication meet the specifics of a methods section. Questions about materials follow a consistent pattern, because each one targets a fact a reader needs to identify, obtain or characterise the material ^[2].

Some fields set explicit thresholds, which hands reviewers a standard to apply. The Journal of Medicinal Chemistry expects tested compounds, whether synthesised or purchased, to be at least 95% pure by an established method such as HPLC; it does not accept spectral data alone as a purity criterion, and it asks for HPLC traces for compounds with in vivo data or a representative set of those tested in vitro ^[1]. Even where a journal sets no number, a reviewer from a neighbouring field will often reach for that one.

Answering the purity question with the right number

The purity question is the one most often answered with the wrong figure. A certificate's HPLC value is a chromatographic area percentage: the share of UV-absorbing material that elutes in the main peak under the stated conditions. It is not the fraction of the weighed solid that is the intended molecule, because salt and water add weight without adding peaks. If the manuscript's concentrations were calculated from gross weight, say so; if they were corrected using a content figure, say where that figure came from and who measured it ^[1].

• Report the figure and the method exactly as the certificate gives them, including the detection wavelength.
• State identity confirmation separately: a mass spectrum shows which molecule is present, not how much else is.
• If an impurity could plausibly be active in the assay, say what is known about the impurity profile — or that it is not known.
• Keep "purity" and "content" as separate words throughout the manuscript; reviewers notice when they are used interchangeably.
• Attribute every figure to its source — supplier certificate, independent laboratory or in-house measurement ^[2].

A reviewer who sees a precise, attributed purity statement usually moves on. One who sees "≥98% pure" with no method and no source will ask all five questions in the table above, and is entitled to.

Why an unnamed supplier attracts scrutiny

A methods section that says "obtained commercially", or names a web storefront with no location, is not merely incomplete; it makes every other question unanswerable. There is no catalogue to check, no lot to request, no certificate to compare. Nature Portfolio's standard is complete descriptions of materials and reagents, and availability to readers with any restriction stated in the paper ^[3]. An untraceable source fails both at once.

Reviewers also know the context. Freedman and colleagues listed biological reagents and reference materials among the four categories of error behind irreproducible preclinical research ^[6], and the research-compound market includes suppliers whose documentation does not survive inspection. A reviewer who presses on a commercial research supplier is applying a prior, not making an accusation. The right response is evidence, not indignation.

Responding when the material is from a commercial research supplier

Say plainly what the material is and where it came from. A research-grade compound from a commercial supplier is an ordinary thing to use; the only question is whether its characterisation supports the conclusion drawn from it.

1. Name the supplier, its location, the catalogue number and the lot in the manuscript itself, not only in the response letter.
2. Attribute the purity and identity data. If they come from the supplier's certificate, say so, and supply the certificate.
3. State what the certificate can and cannot show. Under ISO/IEC 17025, where the laboratory did not do the sampling, its report applies to the sample as received ^[5]; a supplier's certificate describes what the supplier sent for testing.
4. Add your own evidence where you have it — an in-house mass spectrum or chromatogram of the material actually used.
5. Disclose any relationship with the supplier. Donated or discounted material is a potential conflict of interest to be declared in the paper, not something for a reviewer to discover.
6. Where you cannot answer — no lot recorded, nothing left — say so, and state it as a limitation ^[4].

Responses that argue the question is unfair tend to escalate it. Responses that supply the document, name its limits and add data tend to close it.

What to have ready before submission

• The certificate of analysis for the lot used, with its report identifier.
• The lot number as transcribed at receipt, with the dispatch record that ties it to the purchase.
• Storage records from arrival to use.
• A sealed retained portion of the lot, if any remains.
• Any in-house analytical data on the material, with the method used.
• Correspondence with the supplier about the lot or its testing.

Nature Portfolio journals require a reporting summary covering elements of experimental and analytical design, made available to editors and reviewers during assessment ^[3]. The same logic applies to materials whether or not a journal asks: the documents should exist before the question does.

When independent verification becomes necessary

Not every paper needs its compounds re-tested. Verification becomes necessary when three conditions coincide: the conclusion depends on identity or purity; the only evidence is the seller's; and a plausible alternative — an impurity, a wrong sequence, a different salt content — could produce the same observation. Where all three hold, a reviewer is right to ask, and an author is better placed for having asked first.

The strongest answer is a measurement of the material actually used, by a method suited to the question: mass spectrometry for identity, chromatography with a stated method for purity, and a content determination where concentration matters. If the measurement is made in-house, describe how the method was checked — the basics of validating a method in a small laboratory — so that the figure is itself defensible and characterised to the standard a reader needs ^[2].

Pre-empting the question in the manuscript

The best review exchange about provenance is the one that never happens. A methods section that names the supplier, catalogue number and lot; attributes every purity and identity figure; states the concentration basis; supplies the certificate as a supplementary file; and records any in-house confirmation leaves a reviewer little to ask ^[2][4]. It also leaves the next laboratory able to do what the whole exercise is for: obtain the same material and check the result.