1, tannic acid contains nitrogen and can be used to combine with copper to form colored substances for determination. It seems that it must be carried out in ethanol-water solution, and the specific conditions have to be explored by ourselves;

2. If the above method is feasible, turn the wavelength knob on the 72 1 spectrophotometer to find the place with the largest absorption wavelength (there may be two or three peaks) and choose the one with the best effect;

3.72 1 spectrophotometer is actually very easy to operate. When measuring, turn on the machine for a few minutes before choosing the maximum absorption wavelength. Put the reference solution (all equivalent reagent components except the tested object, or water as reference) and the sample solution into the colorimetric tank, put them into the tank box, and cover them. At this time, open the light path, adjust it to the zero point of the scale with the zero adjustment knob, pull out the pull rod, and read the absorbance value of the sample;

4. When changing samples, clean the colorimetric tank with sample solution;

5. You can bring two standard samples: one high and one low;

6, the color of the sample should not be too deep, so as to avoid the numerical value is too large, precision decline.