7.4.1 Electrothermal digestion method 188.8.131.52 Electrothermal plate digestion method Weigh 0.2g ~ 0.3g (accurate to 0.1 mg) sample (7.2) in a 50 ml polytetrafluoroethylene crucible (6.5), add 10 ml after wetting with water Hydrochloric acid (5.1) is heated on a hot plate at 90C ~ 100 in a fume hood to preliminarily decompose the sample. When the digestion solution evaporates to about 3ml remaining, add 9ml of nitric acid (5.2), cover with heat until no obvious particles, add 5ml ~ 8ml hydrofluoric acid (5.3), open the lid, heat the flying silicon at 120C for 30min, cool a little, add 1ml perchloric acid (5.4), heat at 150'C ~ 170'C until white smoke is emitted, and shake the crucible frequently when heating . If there are black carbides on the wall of the crucible, add 1 ml perchloric acid (5.4) and continue heating until the black carbides disappear. Then open the lid and heat the acid until the contents are in the form of liquid beads. ). Add 3 ml of nitric acid solution (5.12), dissolve the soluble residues warmly, transfer the whole amount to a 25 ml volumetric flask, make up to the mark with the nitric acid solution (5.12), shake well, store in a polyethylene bottle, let it stand, take it The supernatant is to be tested. The analysis was completed within 30 days.
Classical method for soil digestion
Graphite digestion instrument + four acid wet digestion + screw cap
1.Accurately weigh the air-dried soil 0.5000 g ± 0.0010 g.
2. 2-3 mL of HF, 2-4 mL of aqua regia, heated with a cover and a tube temperature of 110-120 ° C for 4h.
3. 4-2 mL of aqua regia, 2 mL of perchloric acid, capped, heated at 120 ° C for 4 hours.
4. The temperature of the open tube is 150 ~ 175 ℃, smoke and drive acid, try to get the solution nearly dry (unclear), and lower the temperature slightly.
5. Make up 2 mL of nitric acid in batches at 150 ~ 175 ° C to smoke and drive acid, do not cook.
Repeat 2-3 times until the inside of the tube is clean, agile and clear in color. It is white, light yellow liquid or orange yellow homogeneous gelatinous solid. It usually takes 6h. If it is black and turbid, add perchloric acid, and add 0.5-1 mL of acid in batches. Do not replenish hydrofluoric acid easily. All samples must be replenished in batches! Including blanks! !!
6. Add 2 mL of nitric acid and 10 mL of pure water before leaving the pot (120 ℃), cover and dissolve for 4 h and transfer to a constant volume to 50 mL.