The use of soil analyzers for the determination of heavy metals in the soil, the pretreatment method used concentrated acid open digestion method, but the method of long digestion time, large smoke, easy to lose.
The combination of hydrofluoric acid is used for digestion and digestion with digestion bottles under high temperature and high pressure. The digestion time is short, the environment is less polluted (no smoke) and no loss.
1 Test 1.1 Exposure of aqua regia - HClO4 digestion (acid system 1)
Weigh 01500 g of soil sample in a 500 mL beaker, moisten with a little water, add 5 mL of aqua regia and keep it slightly heated. After vigorous reaction of organic matter, add 41 mL of HClO and continue to heat until the soil sample is pale and 012 mol. / L HNO3 dissolved, filtered into 50 mL volumetric flask, constant volume, determined by atomic absorption spectrometry. This method is Method 1.
1.2 High pressure HNO3-HClO4-HF digestion (acid system 2)
Weigh the soil sample 01500 g, add 2 mL of HNO3, HClO4, and HF to the high-pressure digestion bottle (customized), place it in a 200e muffle furnace and keep at a constant temperature for 2 h, and remove it by filtration in a 50-mL volumetric flask. Absorption assay. This method is Method 2.
2 Results and Discussion 2.1 Comparison of the two digestion methods The same sample was determined by Method 1 and Method 2. The results are shown in Table 1.
Table 1 Test results of the two digestion methods 2.2 Comparison of the same acid digestion system and different digestion methods The control system of No. 4 was compared with the acid system 1 and the acid system 2 at the same time. The results are shown in Table 2.
Table 2 Comparison of Two Acid Digestion Systems and Two Digestion Methods Table 1 and Table 2 show that the open-end or high-pressure methods do not have obvious effects on the results with different acid hydrolysis systems, but hydrofluoric acid is used in high-pressure formulas to clarify the solution. It is better than aqua regia and perchloric acid. Acid hydrolysis system 2 In the high pressure digestion method, the decomposition of the sample is relatively complete, and the result is closer to the given value. In the open method, hydrofluoric acid is often incompletely volatilized during the acid hydrolysis process, and the glassware is easily contaminated.
2.3 Precision and spike recovery. Method 4 and Control 2 were used to determine the precision and spike recovery of Control Sample No. 4. Relative standard deviation: Method 1 Cu 910%, Pb 212%, Cd 116%; Method 2 Cu 411%, Pb 018%, Cd016%. Recovery rates for spiked samples: Method 1 Cu 88%, Pb 80%, Cd 85%; Method 2 Cu 95%, Pb 80%, Cd 90%. It can be seen that the precision and spike recovery of Method 2 are better than those of Method 1.
From the operating steps and digestion effects of methods 1 and 2, Method 2 has the following advantages (Table 3).
Table 3 Comparison of Method 1 and Method 2
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