Effect of tris (hydroxymethyl) aminomethane (Tris) on electrode

Details:

Amino or trimethyl methane has been widely used as a biological buffer for about 35 years. The near ideal properties of this biological buffer are the reason for its popularity. Tris does not absorb water, is easily soluble in water and has high purity. It does not precipitate calcium salts, is stable in solution at room temperature for several months, and does not appear to inhibit many enzyme systems. However, due to the chemical and physical properties of Tris buffer, improper use may lead to incorrect pH measurement of the electrode system.

Effect of pH in Tris buffer on electrode

Biochemists use Tris buffer to control the pH within the physiological range (about 7 to 8 pH), because phosphate can cause adverse reactions with biological substances in the test sample. However, when measuring the pH of these solutions, another type of "adverse side effect" must be recognized, involving the pH electrode system.

Effect of chemical and physical properties of Tris buffer on pH value

Tris in the pH range commonly used for physiological measurements (pH 7 to 7.5) has no large buffer capacity. Therefore, care should be taken when using Tris buffer to control the pH value of the sample. The considerable temperature coefficient (- 0.028ph / ° C) of Tris is also worth considering. For example, if the instrument is calibrated with tris buffer and the tris temperature is 20 ° C, using a pH value of 25 ° C will lead to error. Therefore, temperature pH correlation must be used when Tris is used for standardization. When Tris is used to control the pH value of the sample, the degree of control will depend on the sample temperature. If the sample temperature changes by 2 ° C, the pH control changes by about 0.06 pH units. The required pH control will determine the Zui large temperature fluctuations allowed.

Advantages of Tris buffer

① Because Tris base is highly alkaline, this buffer system can be used only to prepare a buffer with a wide range of pH from acidic to alkaline;

② It has little interference with biochemical process and does not precipitate with calcium, magnesium ions and heavy metal ions.

Disadvantages of Tris buffer

① The pH value of the buffer is greatly affected by the solution concentration. When the buffer is diluted ten times, the change of pH value is greater than 0.1; Tris buffer shall be prepared from high purity Tris and HCl using distilled water or deionized water without CO2.

② The temperature effect is large, and the temperature change has a great impact on the pH value of the buffer, so it must be prepared at the use temperature. The tris HCl buffer prepared at room temperature cannot be used at 0 ℃ ~ 4 ℃;

③ It is easy to absorb CO2 in the air, so the prepared buffer should be tightly sealed;

④ This buffer will interfere with some pH electrodes, so electrodes compatible with tris solution should be used.