Acetic acid water: dilute acetic acid as a solvent

Acetic acid water is sterile water with a small amount of acetic acid (ethanoic acid) added, which makes the solution slightly acidic. The exact composition is on the vial's label.

Like bac water, it is a laboratory supply, not an active substance: it only serves to dissolve a powder or dilute a solution.

How well a peptide dissolves depends on the charge of the chain. Peptides rich in basic amino acids, such as lysine and arginine, carry a positive charge at a slightly acidic pH and then often dissolve better than at neutral pH. A peptide that stays cloudy or keeps particles in bac water sometimes dissolves clear in a slightly acidic solvent.

An acidic solvent does not suit every material. Peptides rich in acidic amino acids dissolve better at a neutral or slightly basic pH. Always follow the material's data sheet or certificate.

How to dissolve a vial step by step is explained in Dissolving peptides.

• Bac water: sterile water with 0.9% benzyl alcohol. The usual choice for most peptides, and suitable for using a vial over several days.
• Acetic acid water: sterile water with dilute acetic acid. For peptides that dissolve poorly at neutral pH.
• If in doubt, dissolve a small part of the material first and see whether the solution turns clear.

• Let the powder vial and the solvent reach room temperature before opening them.
• Add the solvent slowly along the wall of the vial and swirl gently; do not shake.
• Work out the concentration with the peptide calculator: the amount of peptide divided by the volume of solvent.
• Write the solvent, the date, the concentration and the lot number on the vial.

More on storage in Storing peptides.

• Keep the vial cool (2–8 °C) and protected from light, also before it has been pierced.
• Keep a peptide solution in the fridge and do not freeze it.
• Discard a solution that turns cloudy, changes colour or contains particles.

BrabantLabs supplies acetic acid water in 3 ml and 10 ml vials, shipped from the Netherlands.

• A sealed glass vial with a rubber stopper and an aluminium seal.
• A label with the composition, a lot number and an expiry date.
• A volume that suits your work: 3 ml for a single vial, 10 ml if you dissolve several vials.

Is acetic acid water the same as vinegar?

No. It contains acetic acid, the acid also found in vinegar, but at a low concentration in sterile water and filled under sterile conditions. Kitchen vinegar is not sterile and not suitable as a solvent for research material.

Which peptides dissolve in acetic acid water?

Mainly peptides rich in basic amino acids, such as lysine and arginine, that dissolve poorly at neutral pH. The data sheet or certificate tells you which solvent fits.

When do I choose acetic acid water over bac water?

When a peptide does not dissolve clear in bac water, or when the data sheet calls for a slightly acidic solvent. For most peptides, bac water is the usual choice.

How do you store acetic acid water?

Cool (2–8 °C) and protected from light. Once a peptide has been dissolved in it, the solution goes in the fridge; do not freeze it.

• View Acetic acid water in the shop