Buying laboratory reagents so an experiment is reproducible: what an analytical grade actually certifies against a technical one, why lot number belongs in the method rather than in the invoice, and the shelf practice that stops a reagent quietly expiring

Specifying and controlling reagents

1. Match the grade to what the method is sensitive to. Analytical grade for quantitative chemistry, chromatography grade where trace impurities raise a baseline, molecular biology grade where nuclease or nucleic acid contamination matters, and technical grade for cleaning and for bulk uses where purity is irrelevant.
2. Read the certificate of analysis rather than the label. The certificate names the impurities tested and their limits for that lot. Two suppliers' analytical grades can certify different impurity sets, and the one that matters to your method may be on only one of them.
3. Record the lot number with the result, not with the invoice. When an assay drifts, reagent lot is the first variable to check and it is usually unrecorded. Writing the lot into the method record costs nothing and turns a week of investigation into one query.
4. Date every container on receipt and on opening. Shelf life runs from manufacture and many reagents degrade faster once opened. A bottle with no opening date is a bottle nobody can judge, and it will be used long after it should have been discarded.
5. Keep the safety data sheet and label every decant. Every hazardous chemical needs its sheet available and every container other than one in immediate use needs its identity and hazards on it. An unlabelled bottle is the single most common laboratory inspection finding.

Inventory that people actually use

A chemical inventory is a legal expectation as well as a convenience, and the one that works is the one at the point of use: a barcode scanned when a bottle is taken and when it is finished. An inventory maintained by an annual walk round is out of date within a fortnight.

Review for expiry and for the bottles nobody has touched in three years. Disposal of old chemicals is expensive and gets more so as labels fade and contents become uncertain.

Storage and segregation

Segregate by hazard rather than alphabetically, keep flammables in the appropriate cabinet, and use secondary containment for acids and solvents. Alphabetical shelving is how an oxidiser ends up beside an organic solvent.

Temperature sensitive reagents need the right refrigerator, not the nearest one, and anything flammable in cold storage needs a spark free interior. This is a recognised cause of laboratory fires.

Bridging a lot change without losing the assay

Where a reagent materially affects a result, overlap lots: run the new lot alongside the old on the same samples before switching. It costs one run and it separates a lot effect from a real change.

Reserve a lot for the duration of a study where the supplier allows it. Suppliers will usually hold material if asked and will rarely offer, which makes it the cheapest insurance available in a long study.

Common questions

What grade of laboratory reagents do I need?

The grade the method is sensitive to. Analytical for quantitative chemistry, chromatography grade for low wavelength ultraviolet and mass spectrometric detection, molecular biology grade for enzymatic work, technical for cleaning and bulk use.

Does reagent lot really matter?

Often more than the supplier does. Lot to lot variation in serum, enzymes, antibodies and even some salts is real, and an assay that drifts after a reorder is a lot change until proven otherwise. Record the lot with every result.

How long do reagents last once opened?

It depends entirely on the reagent and on how it is stored, which is why the opening date on the bottle matters more than a generic rule. Hygroscopic solids, reducing agents and anything light sensitive degrade fastest.

Should we standardise on one supplier?

For convenience and price, largely yes, with a second source for anything whose absence stops work. What should not vary within a study is the supplier and the lot of the reagents the result depends on.

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