Buffer and solution recipes
The solutions every lab makes constantly, each with the weigh-out calculation worked through, the procedure, and the mistakes that actually cost people a day.
1 M Tris-HCl
Step-by-step recipe for 1 M Tris-HCl at any pH from 7.
- 1 L of 1 M stock
- 20 minutes
0.5 M EDTA pH 8.0
The standard 0.
- 1 L of 0.5 M stock
- 30 minutes
1× PBS
Standard 1× and 10× PBS recipes with exact weigh-outs, the final ion concentrations, and the reason 10× stock precipitates in the cold.
- 1 L of 1× PBS
- 15 minutes
10% (w/v) SDS
The standard 10 % SDS stock, with the weigh-out, the respiratory hazard nobody mentions, and why you must never put it in the fridge.
- 100 mL of 10 % (w/v)
- 15 minutes
50× TAE and 10× TBE
Concentrated TAE and TBE stock recipes, what each is actually good for, and why TBE gels run sharper but ruin downstream enzymatic steps.
- 1 L of concentrated stock
- 25 minutes
LB (Lysogeny Broth)
Recipes for the three common LB formulations, how much agar to add for plates, and the antibiotic working concentrations to add once it has cooled.
- 1 L
- 20 minutes plus autoclaving
The four rules that cover most buffer mistakes
- Check the salt form on the bottle. Hydrates and sodium salts have different formula weights — MgCl₂ is 95.21 g/mol anhydrous but 203.30 as the hexahydrate, and EDTA runs from 292.24 to 372.24 depending on form. Using the wrong number is the single most common weigh-out error.
- Titrate before making up to volume. Acid and base add volume.
- Titrate at the working temperature. Especially with Tris.
- Add divalent cations last, and never into a concentrated phosphate or carbonate solution, or you will precipitate them.
Frequently asked questions
Should I adjust pH before or after making up to volume?
Before. Titrating adds a real volume of acid or base — reaching pH 8.0 in a litre of 1 M Tris takes around 42 mL of concentrated HCl. Adjust the pH first, then make up to the final mark.
Why does my buffer read a different pH in the cold room?
Every buffer has a temperature coefficient, and Tris has an unusually large one (−0.028 pH units per °C). A Tris buffer set to pH 8.0 at 25 °C is near pH 8.6 at 4 °C. Titrate at the temperature you will use it at.
Can I autoclave any buffer?
Most, but not all. Autoclaving darkens Tris slightly, degrades glucose (autoclave it separately and add after), destroys most antibiotics, and precipitates calcium phosphate. Filter-sterilise anything heat-sensitive.