How to prepare Tris buffer with different ionic strength

Details:

 ??Tris buffer is widely used in biological buffer, mainly because of its convenient synthesis, strong buffer capacity and low ionic strength. In some systems, the buffer needs to have specific ionic strength, so how to prepare Tris buffer with different ionic strength

Tris biological buffer large package

Definition of ionic strength of buffer solution

It is relatively simple to prepare Tris buffer. You only need to add HCl in different proportions to Tris solution to obtain buffer solutions with different pH values. It is also relatively simple to determine pH with pH meter, and it is a little more complicated to control different ionic strength of buffer solution. The ionic strength of buffer solution 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 product of the number of corresponding ion charges.

Content of hydrolytic ions in weak electrolytes

It should be noted that the concentration in the ionic strength of the buffer is the mass concentration, not the volume concentration. Buffers such as Tris, bicine and mops are weak electrolytes and are not completely dissociated in aqueous solution. For example, in 0.1M Tris solution, not all Tris are dissociated, and some exist in molecular form in the solution. The dissociated ion ion concentration can be calculated according to the dissociation equilibrium and the dissociation constant PKA and Tris concentration at a specific temperature, and the volume concentration can be converted into mass concentration. Cl - ions are completely dissociated, which is obtained from the amount of hydrochloric acid. H + and oh - ions are calculated from pH, and then the ionic strength can be calculated according to the concentration of each ion.

Adjust the ionic strength of Tris buffer

The buffer solution with specific concentration and adjusted pH has been prepared, and the ionic strength at this temperature is basically determined. What if the ionic strength does not meet the requirements at this time First of all, increasing or reducing the amount of HCl will not work, which will change the pH value of the buffer. At this time, we can add NaCl (or KCl) because the strong electrolyte is completely dissociated. We can directly calculate the added amount to adjust the ionic strength. But if you need to reduce the ionic strength, you can't add electrolyte. You can only reduce the content of tris to slightly reduce the ionic strength. Because Tris has buffer performance, a slight dilution will not affect its pH value.

As for the specific calculation of dissociation equilibrium and ionic strength in buffer solution, you need to consult the data by yourself, or you can calculate the ionic strength through special software. Desheng is a biological buffer manufacturer, which can provide large packaging of Tris, mops, HEPES and other buffers.