Electrophoresis buffers
Electrophoresis buffers
Electrophoresis buffers have (at least) two functions. They maintain pH and provide counterions. Maintaining pH at the electrodes (where water is electrolyzed) requires finite buffering capacity. Decreasing ionic strength or buffer volume, necessitates higher buffering capacity. Ideally one wants high buffering capacity and low conductivity (to minimize electrical heating). Mixing cationic buffers and anionic buffers with similar pK's and low ionic mobilities (as described by Liu, Li and Sommer, Analytical Biochemistry 270, 112-122 (1999)) achieves this effectively. Tris-borate buffers are the classical example of this design.
Looking at the Jovin buffer table one can see that the combination of Tris and Tricine does this nicely. Other suitable combinations should be obvious. The combination of 0.05M Tris and 0.05M Tricine is a good starting buffer. If it works in your system you can lower buffer concentration (permitting higher voltages and reducing cost).
Where acid and base pKas differ there are two potential buffer classes. Where the pKa of the acid is above that of the base one has a "weak acid - weak base buffer" where the majority of acids and bases are unionized. Where pKa of the acid is below that of the base one has a "strong acid - strong base buffer" where the majority of acid and base are electrolytes. The latter buffer type is far more common. The virtues of the two types have not been compared.
It's most convenient and precise to make buffers gravimetrically (volumetrically in the case of liquids). The pH meter (with it's attendant complications) is inadvisable. Where DpH/Dc in minimum, Dc/DpH is maximum which poses risks for electrophoresis buffers. Keep in mind that tertiary amines react with persulfate catalyzing acrylamide polymerization.
Below pH~6 protonation of TEMED dramatically slows acrylamide polymerization.
For additional electrophoresis tips see - Lane, LC (2001) Electrophoresis. Pp 394-396 in Encyclopedia of Plant Pathology. Ed Maloy, OC and Murray, TD. Wiley-Interscience (New York)
New! Sodium borate buffers