Instrument:Quartz digestion tube

Reagent:

1. Nitric acid (HNO3): ρ=1.42g/mL, of superior purity

2. Perchloric acid (HClO4): ρ=1.68g/mL, of superior purity

3. Hydrogen peroxide (H2O2): 30%, analytical grade

Steps:

1. Weigh the tea sample that has been crushed and sieved through a 120 mesh sieve Add 5g to a digestion tube (hard glass tube), add 10mL of nitric acid HNO3 (plug with a perforated tube plug), and let it sit overnight.

2. Insert into the digestion well of the digestion instrument, set the temperature of the digestion instrument to 65 ℃, slowly heat to make the sample bubble and mix, and maintain a constant temperature of 65 ℃ for 15 minutes. 30 minutes in total.

3. Heat up to 135 ℃, hold for 2 hours, and dissolve the sample.

4. If the digestion is not successful, add 5mL of mixed acid HNO3+HClO4 (4+1) after cooling, or add hydrogen peroxide H2O2 dropwise, raise the temperature and maintain it until the solution is transparent.

5. Heat up to 160 ℃ and add acid to about 2mL.