04 — Stability
Aliquoting and freeze–thaw
Ice is not a gentle storage medium. Freeze once per aliquot. Thaw once. Do not refreeze.
Why cycles damage stocks
As water freezes, solutes concentrate in the unfrozen fraction, pH can drift, and ice surfaces nucleate aggregates. Apparent loss of activity in an assay is often loss of intact, soluble peptide.
Preferred hierarchy
- Keep the manufacturer vial lyophilized at the labeled condition — typically −20 °C, desiccated, and dark; −80 °C if the laboratory SOP specifies it.
- Reconstitute only what the week’s work requires, or reconstitute once and split immediately.
- Single-use frozen aliquots at −80 °C when available; otherwise in a validated −20 °C freezer.
- Working solution on ice or at bench only for the length of the assay.
How to aliquot
- Calculate aliquot volume from the assay plate map, not from convenience.
- Use small low-bind tubes or plates already accepted by the laboratory QMS.
- Flash-freeze when the SOP allows; otherwise freeze promptly in the dedicated freezer.
- Log parent batch, stock concentration, aliquot ID, volume, freezer ID, and date.
Thawing
Thaw promptly at a controlled bench temperature, mix gently, use, and discard the remainder. Do not park a thawed aliquot in a refrigerator for the rest of the week as a default habit.
What you are protecting against
- Aggregation and loss of soluble monomer
- Oxidation of Met, Cys, and Trp during the concentrated, oxygen-available phase
- Deamidation of Asn and Gln in pH-shifted unfrozen fractions
General laboratory information for Research Use Only materials. Return to the desk.