A New Lot Arrived: Six Things to Check Before Using It

A lot number changes and everything else on the listing stays the same: same compound, same labelled quantity, same price, same photograph. The vial in the box is from a different synthesis, a different purification and a different fill, and the only document that describes it is its own certificate. Lot changes are routine. Treating them as routine is what makes them safe.

Why a new lot is a new material

Each lot is made, purified, tested and filled as a separate event. Purity drifts by fractions of a percent between runs. Net peptide content can move by several percent because the salt and water fraction depends on the final steps. The impurity profile — which impurities, at what levels — is specific to the run. None of this is a defect; it is what manufacturing in batches means. It is also why a certificate is tied to a lot number and not to a product name.

The six checks

• The lot number on the report matches the vial. Not the product name, not the date — the lot string, character for character. This single check catches most of the problems in this article.
• Purity, read as a figure rather than a badge. Compare it to the previous lot. A move of a few tenths is normal. A move of more than a point or two is worth a question, and the answer is usually visible in the chromatogram.
• Net peptide content. This is the figure that changes most between lots and the one most often missing. If the previous lot was 85% and this one is 78%, the same labelled 10 mg contains noticeably less peptide, and any concentration calculated from the label is wrong by that difference.
• Identity, reported as observed and expected mass. A pass here is binary, but check that the numbers are present rather than a bare “confirmed”.
• The impurity table. A new named impurity, or an existing one that has grown, says something changed in the synthesis. It may be harmless. It is still information worth having before, not after.
• Counter-ion and residual solvent, if reported. A change of salt form between lots changes mass per molecule and can change solubility behaviour, which is the usual explanation for “it dissolved differently this time”.

What to recalculate

• Any concentration derived from net peptide content rather than label weight.
• Any cost comparison that was based on peptide mass rather than vial count.
• Any internal record that refers to “the usual lot”. Replace it with the actual lot string, so that a result six months from now can be traced to the material that produced it.

Keeping it traceable

Record the lot number alongside the date received, the storage condition, the solvent and volume used, and where the certificate is saved. The work is trivial at the time and impossible afterwards. When something behaves unexpectedly, the question is always whether the material changed or the method did, and only a record that ties a result to a lot can answer it. Lot numbers and traceability covers the record-keeping side; comparing two reports covers what to do when two lots disagree.

What to ask a supplier

• Whether a new certificate is issued for every lot, or one report covers several.
• Whether you are told when the lot changes on a repeat order, or have to notice.
• Whether the previous lot’s report is still available, since a comparison needs both.
• Which lot will ship before the order is placed, if the comparison matters to the work.

All products referenced on this site are supplied for laboratory research use only, and are not for human or veterinary use.