About buffer solutions

Buffer solutions are used to maintain pH in water solution at a constant temperature. Buffers are mixtures of weak acids paired with weak bases. A good buffer — buffering capacity — works to minimize change in pH even when strong acids or strong bases are added to the solution. Neutral or nearly neutral pH is desirable when working with biological molecules because we believe these represent the molecules as they are in life.

Briefly, pH is a measure of how acid (basic) a solution is. Acids give up hydrogen ions more readily than do bases. Reactions of acids can be followed as dissociation of [HA] [H+][A-], where HA is the acid and A- is the conjugate base. Different chemicals will give up different amounts of H+ at neutral pH, and that is defined as the chemical’s pKa (acid dissociation constant).

There are many formulations of buffer solutions, TBE and TAE are common buffers used in electrophoresis of nucleic acids and protein solutions. We chose chemicals for buffers based on their pKas; we want + 1 pH.

For example, Tris is a weak base, Borate is a weak acid. EDTA is added in low amounts and so contributes negligibly to pH buffering capacity.

	$20 ^{\circ}C$	$25 ^{\circ}C$
Tris base	8.3	8.1
Boric acid	9.28	9.24
Acetate acid	4.76	4.76

Tris: The temperature coefficient, $\frac{\Delta \ pK_{a}}{\Delta T}$ , is approximately $-0.031 ^{\circ}C$ .

Boric: The temperature coefficient is approximately $-0.0066 ^{\circ}C$ .

Acetate: The temperature coefficient is negligible, approximately $-0.0002 ^{\circ}C$ .

Working and Stock solutions

Stock solutions, often labeled as 10X or 50X, are highly concentrated, stable preparations made in advance to save time and reduce errors in the laboratory. For example, it is much easier to accurately pipette 1 mL from a 10x stock solution than it is to accurately pipette 100 µL of a 1x working solution, reducing the impact of pipetting errors. Stock solutions are made ahead of time; working solutions are made just in time: they are diluted to a 1X final, usable concentration, known as the working solution.

Proper labeling

Minimum requirements for labeling stock solutions include the full chemical name, the concentration or dilution, the date the solution was prepared, the course number of the laboratory class, and the initials of the person who prepared the solution. For well-known solutions like TBE or TAE, the initials are appropriate instead of the full chemical names because they are unambiguous and well recognized.

Links to recipes

References

Millipore-Sigma Buffer Reference Center