Handling lyophilised research peptides: a practical checklist for the lab

Synthetic peptides arrive in most labs as a small amount of white, freeze-dried powder in a sealed vial. That format is chosen for a reason: with the water removed, a peptide is far more stable than it would be in solution. But the stability is conditional.

What happens between the courier’s van and the first experiment can decide whether the material in the vial still matches the numbers on its paperwork. This checklist covers the steps that tend to get skipped.

1. Checks on arrival

Start before the vial goes anywhere near a freezer.

• Inspect the packaging. Note whether any cold packs were still cold, whether the outer box was damaged, and how long the parcel was in transit. Lyophilised peptides generally tolerate short periods at ambient temperature, but a long, hot transit is worth recording.
• Check the seal and the cake. The powder should sit as a dry cake or loose powder. A collapsed, glassy or sticky appearance can indicate moisture got in.
• Match the label to the paperwork. Peptide name, sequence or catalogue number, quantity and lot number on the vial should agree with the delivery note and the certificate of analysis (COA). If they don’t, quarantine the vial and query it before use.
• Log it. Record date received, supplier, lot number, quantity, condition on arrival and storage location. This takes a minute and saves hours later.

2. Temperature, light and moisture

For most peptides, long-term storage of the lyophilised powder at -20°C or below is standard practice, with -80°C preferred for longer holds or sensitive sequences. Short-term storage at 2 to 8°C is usually acceptable for days to weeks, but follow the supplier’s datasheet where one exists.

Moisture is the bigger risk in day-to-day handling. Lyophilised peptides are often hygroscopic, and a cold vial opened in a warm room will pull condensation straight onto the powder. Two habits prevent most problems:

• Let the vial reach room temperature in a desiccator before opening it.
• Open it for as short a time as possible, then reseal, purge with dry nitrogen or argon if available, and return it to the cold.
   

Light matters too, particularly for sequences containing tryptophan or other photosensitive residues. Amber vials or storage in a closed box are a simple safeguard.

Sequence also affects stability. Peptides containing cysteine, methionine or tryptophan are prone to oxidation, and those containing asparagine or glutamine can deamidate. These are worth flagging in the inventory so they get extra care.

3. Aliquoting to avoid freeze–thaw cycles

Every freeze–thaw cycle is an opportunity for degradation, aggregation and moisture uptake. The fix is to aliquot early.

• Plan how much is needed per experiment and divide the material into single-use portions as soon as practical.
• If aliquoting as a solution, choose the solvent and buffer for the sequence and the assay (sterile water, dilute acid or a small proportion of an organic solvent for hydrophobic sequences), and filter if the application requires it.
• Peptides in solution are much less stable than lyophilised powder. Store solution aliquots frozen, avoid repeated thawing, and set a clear discard date.
• Label every aliquot with the peptide, lot number, concentration, solvent, date prepared and preparer’s initials.

4. Labelling and lot traceability

When a result looks odd, the first question is often “which lot was that?”. Good traceability lets that be answered in seconds.

• Keep the lot number attached to the material at every step, from parent vial to aliquots to the experiment record.
• Store the COA for each lot alongside the inventory entry, not in someone’s inbox.
• Record when a vial was first opened and how many times it has been accessed.
• If a lot is retired, note why: used up, expired or suspected degradation.

5. Reading the HPLC and MS figures on a certificate of analysis

A COA is only useful if it’s read critically. The two figures that matter most for identity and purity are usually HPLC and mass spectrometry.

HPLC purity is normally reported as a percentage, calculated as the area of the main peak relative to the total area of all peaks detected, typically at 210 to 220 nm where the peptide bond absorbs. Points to check include:

• Is the chromatogram itself included, or only a number? A trace lets you see the main peak and any impurities.
• What were the method conditions (column, gradient, wavelength)? Purity figures from different methods are not directly comparable.
• Does the sample ID or lot on the chromatogram match the vial?
   

Mass spectrometry confirms identity by comparing the observed mass with the theoretical mass of the sequence. Check the following:

• The theoretical mass is stated and matches the expected sequence, including any modifications such as amidation or acetylation.
• The observed mass (or the charge states shown for ESI-MS) agrees within the stated tolerance.
   

Purity is not the same as peptide content. A peptide that is 98% pure by HPLC may still contain a substantial proportion of counter-ions (often trifluoroacetate from purification) and residual water by weight. Net peptide content, where reported, tells you how much of the powder is actually peptide. It matters when making up solutions to a known concentration.

Know what the COA does not cover. A COA describes the specific lot that was tested. It is worth confirming whether testing was done in-house or by an independent lab, and whether the document relates to the exact lot in hand. Where results matter, independent verification of identity and purity is good practice.

6. A summary for the lab bench

• Inspect, match lot numbers to paperwork and log on arrival.
• Store lyophilised powder cold (typically -20°C or below), dry and dark.
• Warm vials to room temperature in a desiccator before opening.
• Aliquot early into single-use portions; avoid freeze–thaw cycles.
• Label every aliquot with lot, concentration, solvent and date.
• Keep each lot’s COA with the inventory record.
• Read HPLC and MS data critically, and don’t confuse purity with peptide content.
   

None of this is complicated, but it’s easy to let slip when a project is busy. A few minutes of discipline on arrival and at the bench keeps the material reliable and the results defensible.

*Form Laboratories is an online research peptide supplier based in Perth, WA. Its products are supplied for laboratory research use only and are not for human or animal use. For more information, visit formlaboratories.com.

Image credit: iStock.com/LumiNola