Salt effect in Tris and mops biological buffer

Details:

In biochemical detection, when we select buffers Tris, mops and caps, we first consider the dissociation constant PKA and buffer range of the buffer. In addition, the salt effect of the detection system can not be ignored, which will also affect the experimental results.

Most biological systems are affected by salt. In addition to meeting the pH value range required by the system, the buffer selected for detection should also ensure as little salt effect as possible. In special cases, salt will also be added during the experiment to adjust and increase the salt effect. Buffers such as Tris, bicine and mops are usually composed of conjugated acid-base pairs and belong to weak electrolytes. If the system contains strong electrolyte (strong acid, strong base), the weak electrolyte will produce salt effect in contact with it. When the solubility decreases, it is salting out effect; On the contrary, it is salting in.

Definition of salt effect:

When a strong electrolyte without the same ions as the weak electrolyte is added to the solution of the weak electrolyte, due to the increase of the total concentration of ions in the solution and the enhancement of the interaction between ions, the opportunity of the combination of anions and cations dissociated by the weak electrolyte to form molecules is reduced, so that the molecular concentration of the weak electrolyte is reduced, the ion concentration is correspondingly increased, and the degree of dissociation is increased, This effect is called salt effect.

For example, Tris, mops and HEPES belong to weak electrolytes, while hydrochloric acid and sodium hydroxide used for buffer pH adjustment belong to strong electrolytes. If the concentration of the latter is too high, it may increase the dissociation degree of buffer and affect the pH balance of buffer. Therefore, in some experiments, Tris acetic acid or Tris glycine is used instead of Tris hydrochloric acid. Both acetic acid and glycine are weak electrolytes, while hydrochloric acid is a strong electrolyte.

When 0.1mol/l NaCl solution is added to 0.1mol/l acetic acid solution, sodium chloride is completely ionized into sodium ions and chloride ions, so that the total number of ions in the solution increases sharply and the electrostatic interaction between ions is enhanced. At this time, acetate ion and hydrogen ion are surrounded by many different ions (sodium ion and chloride ion). The chance of acetate ion combined with hydrogen ion to form acetic acid is reduced, and the ionization degree of acetic acid is increased (from 1.34% to 1.68%).

Now there are many Tris buffer systems, such as Tris glycine, Tricine, BIS Tris, etc., which can not only meet the pH required by the system, but also meet the appropriate salt effect of different detection systems. Desheng is a manufacturer of biological buffer, which can provide raw materials for Tris and its derivative buffer system.