In daily practical experiments, when the liquid samples are collected correctly, we often do not need a pure solution to carry out experiments. In order to get better and more accurate detection results, diluent water or other solutions will be added to obtain the solution with lower concentration. In this process, the solvent diluent is needed. In many laboratories, it is generally believed that direct preparation of buffer by diluent reagent will be more accurate and cheaper, which is not in line with the fact, because the quality of buffer is related to the purity of reagent, the accuracy of reagent weighing, the quality of purified water and other factors such as temperature, preparation container and so on.