Tris, or tris(hydroxymethyl)aminomethane, has been widely used as a pH buffer in biological media 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 for several months at room temperature, and does not seem to inhibit many enzyme systems. However, due to the chemical and physical properties of Tris buffer, improper use may lead to erroneous pH measurement of the electrode system.
The influence of pH in TRIS buffer on electrode
Biochemists use TRIS buffers to control the pH within the physiological range (approximately 7 to 8 pH), because phosphate can cause adverse reactions with biological substances in the test sample. However, when pH measurements are to be made on these solutions, another type of "adverse side reaction" must be recognized, involving the pH electrode system.
The influence of chemical and physical properties of Tris buffer on pH
Tris, which is commonly used for physiological measurement (pH 7 to 7.5), does not have a large buffer capacity. Therefore, caution should be exercised when using tris buffer to control sample pH. The rather large temperature coefficient of tris (-0.028pH/ C) is also worth considering. For example, if the meter is calibrated with tris buffer and the tris temperature is 20 C, using a pH value of 25 C will cause errors. Therefore, temperature pH dependence must be used when using tris for standardization. When using tris to control the pH 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 maximum allowable temperature fluctuations.
Advantages of Tris buffer
Because the Tris base is highly alkaline, this buffer system can be used to prepare buffers with a wide range of pH values from acidic to alkaline;
It has little interference to the biochemical process, and does not precipitate with calcium, magnesium ions and heavy metal ions.
Disadvantages of Tris buffer
The pH value of the buffer is greatly affected by the concentration of the solution. The buffer is diluted ten times, and the pH change is greater than 0.1; the Tris buffer should be prepared from high-purity tris and HCl using distilled or deionized water without CO2.
The temperature effect is large, and the temperature change has a great influence on the pH value of the buffer, so it must be prepared at the use temperature, and the Tris-HCl buffer prepared at room temperature cannot be used at 0 C to 4 C;
It is easy to absorb CO2 in the air, so the prepared buffer should be tightly sealed;
This buffer has a certain interference effect on some pH electrodes, so use an electrode compatible with Tris solution.
