Syringes, Filters and Tubes: Consumables for Peptide Work
Membrane choice, dead volume and low-binding plastics are not incidental. The wrong ones remove peptide without leaving any trace that they did.
Reconstitution needs a small number of consumables, and the choices among them are not arbitrary. Getting them wrong introduces contamination, particulates, or loss of the peptide onto surfaces — none of which show up as an obvious error.
Syringes and needles
For transferring solvent into a vial and drawing solution out, the relevant properties are graduation resolution and dead volume.
- Graduations should match the volume being measured. Measuring 0.3 ml on a 5 ml syringe is guesswork. Use the smallest syringe that holds the volume.
- Dead volume — the liquid retained in the hub and needle after the plunger bottoms out — can be a meaningful fraction of a small transfer. Low-dead-space designs reduce it.
- Needle gauge matters mainly for the stopper. A fine needle makes a smaller hole, so a multi-use vial stopper reseals better. Coring — punching a fragment of rubber into the vial — is reduced by inserting at an angle, bevel up.
Syringes should be single-use. Reusing them across compounds is the simplest way to cross-contaminate a batch of work.
Sterile filtration
Filtration through a 0.22 µm membrane removes bacteria and particulates from a solution. Two things it does not do: it does not remove endotoxin, which is far smaller than the pore size, and it does not remove aggregates below the cut-off.
Membrane choice matters more than most people expect, because peptides adsorb to some materials:
| Membrane | Protein/peptide binding | Notes |
|---|---|---|
| PES (polyethersulfone) | Low | Usual first choice for aqueous peptide solutions |
| PVDF | Low | Good chemical compatibility |
| Cellulose acetate | Low | Good for aqueous, poor solvent resistance |
| Nylon | High | Avoid — binds peptide |
| PTFE | Variable | For organic solvents |
At dilute concentrations, adsorptive loss to a filter can be a significant fraction of the material. Where the concentration is low and sterility is essential, pre-rinsing the filter or pre-saturating it is standard practice.
Filtration also adds an air–liquid interface and shear, both of which promote aggregation. It is worth doing when the protocol requires sterility, and not worth doing as a precaution.
Tubes and adsorption
Peptides stick to plastic and glass. For solutions above roughly 0.1 mg/ml the loss is usually negligible; below that it is not, and the effect is worse at higher surface-to-volume ratio — which means small aliquots are the most affected.
- Low-binding polypropylene tubes for dilute solutions.
- Silanised glass where glass is required.
- Plain polystyrene is the worst common option for dilute peptide.
Vials and stoppers
Amber glass for light-sensitive sequences — those containing tryptophan, tyrosine or phenylalanine. Butyl rubber stoppers are standard and reseal reasonably after fine-gauge puncture; repeated punctures at the same point eventually fail.
Wipe the stopper with alcohol and let it dry before each puncture. Alcohol carried into the vial on a wet stopper is a solvent you did not intend to add.
What is worth spending on
In order: low-binding tubes if working dilute, appropriately sized syringes, and the right filter membrane if filtering at all. Everything else is commodity.
Our reconstitution guide covers the procedure, the diluent guide covers the water, and the endotoxin article covers why filtration is not a substitute for testing.
All products and information referenced are for in-vitro research and laboratory use only. Nothing here is medical advice, and no therapeutic claim is made or implied.