An unlabelled tube in a freezer is waste regardless of what is in it, and a tube labelled only with a compound name is very nearly as bad. The information that makes an aliquot usable six months later is not the compound — it is the concentration, the lot and the date, because those are the three things that cannot be recovered by looking at it.
The five fields
| Field | Why it cannot be recovered later |
|---|---|
| Compound | Clear solutions are indistinguishable |
| Concentration | Depends on the fill, the volume and the content correction |
| Lot number | The unit that varies between batches |
| Date prepared | Starts the stability clock for the solution |
| Diluent | Changes what a vehicle control has to match |
Five fields will not fit legibly on a 0.5 mL tube, which is the real constraint and the reason most labelling is inadequate. The usual resolution is a short unique code on the tube and the full record elsewhere — a notebook, a sheet, a file — keyed to that code.
What is the minimum that works?
A code and a date. If the code resolves to a record carrying everything else, the tube needs nothing more, and a code plus date is small enough to write legibly even on a small cap-less tube.
What fails is a code with no record, which is common and is exactly as useless as no label. The code is a pointer; if nothing is pointed at, it carries no information. The record is the part that actually has to exist.
Why not write on the lid?
Because lids get swapped. Opening several tubes at once and replacing the caps in a different order is easy to do and impossible to detect afterwards, and every label on every lid is then wrong with nothing to indicate it.
Lids also take the most abuse — they are gripped, twisted and wiped — so writing wears off them fastest. The side of the tube is the right surface, with the lid used at most for a colour code that duplicates rather than replaces it.
What survives a freezer and what does not
Three failure modes account for nearly every unreadable tube.
Frost and condensation. Water condenses on cold surfaces, and repeated cycles work ink loose. Labels applied to a cold tube never adhere properly in the first place, because the adhesive sets against a film of moisture.
Solvent. Ethanol and isopropanol dissolve most marker inks. A tube wiped down with alcohol, which is routine, can be blank afterwards. This is the commonest single cause and the easiest to avoid.
Abrasion. Tubes in a box rub against each other and against the dividers every time the box is moved, and ink on a smooth plastic surface does not survive much of that.
The combination that works is a cryogenic-rated label or marker, applied to a dry tube at room temperature, left to set before freezing. Writing on a frosted tube pulled from a freezer fails on all three counts at once.
Does the marker really matter?
Yes, more than most people expect. Ordinary permanent markers are permanent against water and not against alcohol, and they are not formulated for repeated thermal cycling. Laboratory cryogenic markers and cryo-labels are designed for the combination of cold, moisture and solvent.
The cheap test is to write on a spare tube, freeze it, thaw it, wipe it with alcohol, and see what remains. That takes a day and settles the question for every tube afterwards — a worthwhile check if a freezer already contains tubes nobody can read.
What about the parent lot?
It is the field most often dropped and the one most worth keeping. An aliquot inherits everything from the vial it came from — the content figure, the impurity profile, the purity — and those differ between batches.
Without the lot on the record, an aliquot cannot be tied back to a certificate, which means its concentration cannot be verified and a discrepancy cannot be investigated. The lot transcribed from the vial on arrival is what makes this possible; dropping it at the aliquoting step throws away the traceability that was already established.
A workflow that holds up
The labelling has to happen at the same moment as the aliquoting, not afterwards, because afterwards is when tubes get mixed up.
- Label the empty tubes first. Before anything is dispensed, while they are dry and at room temperature and there is no time pressure.
- Write the record as you go. Compound, concentration, lot, date, diluent, number of tubes, and where they are going.
- Aliquot into the pre-labelled tubes. Single-use volumes, so no tube is ever thawed twice.
- Note the box and position. A tube that exists but cannot be found is the same as a tube that does not exist.
- Freeze. Label already dry and set.
How should the volume be chosen?
By what a single experiment consumes, plus a margin for the volume lost to the tube wall and the pipette tip. Too large and material is wasted or the tube gets re-frozen; too small and two tubes are needed, which reintroduces the handling the aliquoting was meant to avoid.
Very small volumes have their own problem: a high surface-to-volume ratio means proportionally more material adsorbs to the tube wall. Somewhere around a few tens of microlitres is usually the practical floor for a dilute solution.
Is a printed label better than a marker?
For anything that will be stored long-term or in quantity, yes. A cryogenic printed label carries more text legibly than handwriting on a curved surface, it is consistent across tubes, and it does not depend on anyone's handwriting at the end of a long session.
For a handful of tubes used within weeks, a good marker is adequate and faster. The decision is about how long the tubes will exist and how many of them there are, rather than about rigour.
What about aliquots of supplies rather than peptide?
The same discipline, with one addition: note the date the parent container was opened, not only the date the aliquot was made. A multi-entry solvent bottle has its own usable window from first entry, and an aliquot drawn from it late in that window is not equivalent to one drawn early.
This matters most where the solvent carries a preservative whose effectiveness is time-limited. For a compound reconstituted once and another reconstituted from the same bottle weeks later, the two solutions differ in a way neither label would show unless the bottle's open date was carried through.
Why this is the step that fails
Labelling fails more often than any other part of the aliquoting workflow, and the reason is structural rather than careless: it is the last step, done when the interesting work is finished and the material is already in the tubes.
Doing it first inverts that. Labelled tubes waiting to be filled turn labelling into preparation rather than cleanup, and preparation is the part of a protocol people reliably complete.
The second structural problem is that the cost of failure is deferred. An unlabelled tube causes no trouble on the day it is made; it causes trouble months later, usually to somebody else, which is exactly the shape of problem that does not self-correct.
What should happen to a tube nobody can identify?
It should be discarded, and that is worth saying plainly because the usual outcome is that it sits in the freezer for years. An unidentifiable aliquot cannot be used for anything that will be written up, because its concentration, lot and age are all unknown.
Keeping it occupies space and creates a hazard of a different kind: the chance that someone eventually uses it on the assumption that it is what the box suggests. Disposal is the honest answer, and the lesson belongs in the labelling habit rather than in the freezer.
Is a freezer inventory worth maintaining?
For more than a few dozen tubes, yes, and it does not need to be sophisticated. A sheet listing code, contents, concentration, lot, date and box position is enough, and it is the thing the tube's short code points at.
What makes an inventory work is that it is updated at the moment tubes are made and the moment they are used up, rather than reconstructed periodically. An inventory that disagrees with the freezer is worse than none, because it is trusted.
Does any of this apply to the parent vial?
Yes, and it is the step people skip because the vial arrives already labelled. A manufacturer's label carries the compound, the quantity and the lot; it carries nothing about your custody — not the date it arrived, not the date it was opened, not the date it was reconstituted.
Those three dates are what let a vial found later be reasoned about, and they matter more than any date the supplier printed. Adding them takes a marker and ten seconds at the moment each event happens.
How long should a record outlive the material?
Longer than the tubes do. The usual reason to go looking is a question about a result, and results are discussed long after the material behind them is gone — so a record that is discarded when the last tube is used has been thrown away exactly when it starts to be needed.
Keeping the sheet with the experimental data rather than with the freezer is the simplest fix, because the data is what survives.
All products referenced here are supplied for laboratory and research use only. They are not drugs, foods, supplements or cosmetics, and are not for human or veterinary use.
