Aliquoting Reagents into Sterile Vials: A Practical Guide

Splitting a reagent into small, single-use portions (aliquots) is one of the simplest ways to protect it. Every time a stock bottle is opened, it risks contamination; every freeze–thaw cycle can degrade sensitive components. This guide covers how to aliquot buffers and reagent solutions into sterile vials, and how to label and store them.

Why aliquot?

• Contamination is contained. If one vial is contaminated, you lose one aliquot, not the whole batch.
• Fewer freeze–thaw cycles. Thaw only what you need for the experiment.
• Consistency. Every experiment draws from material handled the same way, which makes results easier to compare.
• Traceability. Labelled aliquots tie each experiment back to a batch and preparation date.

What you need

• A laminar flow hood or biosafety cabinet (or the cleanest area available).
• 70% ethanol or isopropyl alcohol for wiping surfaces.
• Sterile borosilicate glass vials sized to one experiment’s worth of reagent.
• Sterile syringes or pipettes, and a 0.22 µm syringe filter if the solution is to be sterile filtered on the way in.
• Luer lock caps to close syringes or filter outlets between steps.
• Solvent-resistant labels or a fine marker.

Step by step

1. Plan the aliquot size. Work out the volume one experiment uses and add a small margin. Several small aliquots beat one large one.
2. Prepare the work area. Switch on the hood for the time the manufacturer recommends, wipe the surface with 70% alcohol and lay out everything you need so you are not reaching in and out.
3. Label the vials first. Contents, concentration, batch or lot, date and initials. Labelling afterwards risks mix-ups.
4. Wipe the stock container and any stoppers with 70% alcohol and let them air-dry; alcohol only disinfects once it has evaporated.
5. Transfer. Draw the reagent into a sterile syringe and, if required, fit a 0.22 µm filter and dispense through it into each vial (see our syringe filter guide). Do not touch the vial opening or the inside of caps.
6. Close each vial at once and check the seal.
7. Record the batch, number of aliquots and storage location in your notebook or inventory.

Storage

Material	Typical storage
Buffers such as PBS and saline	Room temperature or 2–8 °C, sealed
Reagent stocks in DMSO	As the reagent’s data sheet states; DMSO freezes at about 18 °C, so it is solid in a fridge
Heat- or light-sensitive reagents	Follow the supplier’s data sheet; use amber vials or foil, and freeze at −20 °C or below where stated

• Borosilicate glass handles freezing and temperature changes well, but leave headspace for liquids that expand when frozen.
• Thaw at room temperature or on ice, mix gently, and do not refreeze a thawed aliquot.
• Discard any aliquot that looks cloudy, has particles or has a damaged seal.

Related: dilution and molarity calculator · PBS and buffer recipes. Supplies: sterile 10 mL vials, PES syringe filters, luer lock caps, WFI water.

General laboratory guidance; follow your own institution’s procedures where they differ. Union Biolabs products are supplied for laboratory research use only.