12% SDS-PAGE resolving gel recipe
Composition of a 12% acrylamide resolving gel. Separates about 15–100 kDa, especially 20–60 kDa. 10 mL casts about two 1.0 mm mini gels.
🧮 Volume calculator
| Component | Amount | Final concentration (1X) |
|---|---|---|
| Water | 3.3 mL | |
| 30% acrylamide/bis (29:1) | 4 mL | 12% |
| 1.5 M Tris-HCl pH 8.8 | 2.5 mL | 375 mM |
| 10% SDS | 100 µL | 0.1% |
| 10% APS (fresh) | 100 µL | 0.1% |
| TEMED | 4 µL | 0.04% |
Steps
- Mix water, acrylamide, Tris and SDS.
- Add APS and TEMED last, swirl gently and pour immediately between the plates (leave ≈1.5 cm for the stacking gel).
- Overlay with isopropanol or water to level the surface and let it set for 20–30 min.
- Pour off the overlay, rinse with water and add the stacking gel.
Good to know
- Setting time depends on temperature and APS freshness: too fast → less TEMED; not setting → make fresh APS.
- Approximate ranges: 8% 30–200 kDa · 10% 20–150 kDa · 12% 15–100 kDa · 15% 10–60 kDa.
⚠ Safety Unpolymerised acrylamide is a neurotoxin — wear gloves and prefer ready-made solutions to powder. Polymerised gel is much safer.
FAQ
When is a gradient gel (4–20%) better?
When proteins of very different sizes must be seen together or the size is unknown. They are hard to cast, so most labs buy them.
This is a widely used standard composition. Amounts depend on the hydrate form and purity of your reagents — check the formula weight (FW) on the bottle and follow your institution's safety rules and the manufacturers' instructions.