How to prepare Tris buffers with different ionic strengths

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Tris buffer is a common type of biological buffer, mainly because of its convenient synthesis, strong buffering capacity, and the advantages of low ionic strength. And in some systems, the buffer needs to have a specific ionic strength, so how to prepare Tris buffers with different ionic strengths?

Tris biological buffer large package

Definition of buffer ionic strength

To prepare Tris buffer, it is relatively simple. You only need to add different proportions of hydrochloric acid HCl to the Tris solution to obtain buffer solutions with different pH values. It is also relatively simple to use a pH meter to measure pH, but to control the buffer Different ion intensities are a little more complicated. The ionic strength of the buffer is a function of the mass concentration of all ions in the solution, which is half of the sum of the product of the mass concentration of all ions and the square of the corresponding ion charge.

The content of weak electrolyte hydrolyzed ions

It should be noted that the concentration in the ionic strength of the buffer is a mass concentration, not a volume concentration. Buffers such as Tris, Bicine, and MOPS are weak electrolytes and are not completely dissociated in aqueous solutions. For example, in a 0.1M Tris solution, not all Tris are dissociated, and some exist in the solution as molecules. The dissociation can be calculated based on the dissociation equilibrium and the dissociation constant pKa and Tris concentration at a specific temperature. The calculated ion concentration can be converted into mass concentration by volume concentration. Cl- ions are completely dissociated from the amount of hydrochloric acid, H+ and OH- ions are calculated from pH, and then the ionic strength can be calculated based on the concentration of each ion.

Adjust the ionic strength of Tris buffer

I have prepared a buffer solution with a specific concentration and adjusted pH, and the ionic strength at this temperature is basically determined. What if the ionic strength does not meet the requirements at this time? It is impossible to increase or decrease the amount of HCl first, and it will change the pH of the buffer. At this time, we can add NaCl (or KCL), because the strong electrolyte is completely dissociated, and the added amount can be directly calculated to adjust the ionic strength. But if you need to reduce the ionic strength, you can't add electrolytes. Only reduce the content of Tris to slightly reduce the ionic strength. Because Tris has buffering properties, a slight dilution will not affect its pH.

As for the specific calculation of the dissociation equilibrium and ionic strength in the buffer, you need to consult the data yourself, or you can calculate the ionic strength through special software. Desheng is a manufacturer of biological buffers and can provide large packages of various buffers such as Tris, MOPS, HEPES and so on.