How to make a 10% (w/v) SDS stock
The standard 10 % SDS stock, with the weigh-out, the respiratory hazard nobody mentions, and why you must never put it in the fridge.
10% (w/v) SDS 100 mL of 10 % (w/v)
Preparation time about 15 minutes.
| Component | Formula weight | Amount |
|---|---|---|
| Sodium dodecyl sulfate | 288.38 g/mol | 10.0 g |
| Deionised water | — | to 100 mL |
Procedure
- Wear a mask. SDS powder is extremely fine and is a serious respiratory irritant. Weigh it in a fume hood or a balance enclosure, and move slowly — the powder aerosolises from the smallest air current.
- Add the powder to about 80 mL of water and stir gently. Vigorous stirring makes it foam like detergent, because it is one.
- Warm to about 68 °C if it is dissolving slowly. Do not boil.
- Adjust to pH 7.2 with a few drops of concentrated HCl if your protocol calls for it. Many do not bother.
- Make up to 100 mL. Store at room temperature.
What matters here
Never refrigerate it
SDS crystallises out below about 15 °C and will not readily redissolve. A 10 % stock kept at room temperature lasts essentially indefinitely; the same stock in a cold room is ruined.
It denatures everything
SDS binds proteins at roughly 1.4 g per gram of protein, which is what makes SDS-PAGE work — the uniform charge-to-mass ratio means migration tracks size. It also means any enzyme it touches is dead.
Incompatible with potassium
Potassium dodecyl sulfate is poorly soluble, so SDS precipitates in potassium-containing buffers. This is exploited deliberately in plasmid miniprep neutralisation, where potassium acetate crashes out the SDS along with genomic DNA and protein.
Frequently asked questions
Solution has crystallised
It got cold. Warm to 37–68 °C with gentle stirring; if it has been cold a long time, make it fresh.
Foams uncontrollably
Stir slower and warm it. Foam is cosmetic but makes accurate volume adjustment impossible until it settles.