HJ 658-2013Soil. Determination of organic carbon. Combustion oxidation-titration method (English PDF)

Foreword

To implement the "Environmental Protection Law of the People's Republic of China", protect the environment, protect human health, and regulate organic carbon in soil the method of determination is to develop this standard.

This standard specifies the combustion oxidation-titration method for the determination of organic carbon in soil.

This standard is the first release.

This standard was formulated by the Science and Technology Standards Department of the Ministry of Environmental Protection.

This standard is mainly drafted by. Dalian Environmental Monitoring Center.

This standard is verified by. Anshan Environmental Monitoring Center Station, Jinzhou Environmental Monitoring Center Station, and Yingkou City Environmental Monitoring Xinzhan, Fushun Environmental Monitoring Center Station, Changchun Environmental Monitoring Center Station, Harbin Environmental Monitoring Center Station.

This standard was approved by the Ministry of Environmental Protection on August 16, 2013.

This standard has been implemented since September 1, 2013.

This standard is explained by the Ministry of Environmental Protection.

Determination of soil organic carbon - combustion oxidation - titration

1 Scope of application

This standard specifies the combustion oxidation-titration method for the determination of organic carbon in soil.

This standard applies to the determination of organic carbon in soil, and is not applicable to the determination of organic carbon in sludge-contaminated soil.

When the sample amount is 0.50 g, the detection limit of this method is 0.004%, the lower limit of determination is 0.016%, and the upper limit of measurement it is 4.00%. When the organic carbon content in the sample is high, the sampling amount can be reduced, but the minimum can not be less than 0.050 g.

2 Normative references

The contents of this standard refer to the following documents or their terms. For undated references, the valid version is appropriate.

Used in this standard.

HJ/T 166 Technical Specifications for Soil Environmental Monitoring HJ/T 613 Determination of dry matter and moisture in soils - Gravimetric method

3 Principle of the method

The air-dried soil sample is heated to more than 900oC in a furnace, and the organic carbon in the sample is oxidized to carbon dioxide.

The carbon dioxide is absorbed by an excess of cesium hydroxide solution to form a cerium carbonate precipitate, and the remaining cerium hydroxide after the reaction is dissolved with oxalic acid.

The droplet is determined, and the volume difference of the oxalic acid standard solution consumed by the blank titration and the sample titration is used to calculate the carbon dioxide generation, according to the dioxin.

The amount of carbon produced is used to calculate the organic carbon content in the soil.

4 Interference and elimination

When the sample is heated above.200 °C, all carbonates are completely decomposed to produce carbon dioxide.

Positive interference is generated and can be removed by adding an appropriate amount of hydrochloric acid.

Carbon dioxide in the air produces a positive interference equivalent to 0.2% organic carbon, which is removed by subtracting the blank.

5 Reagents and materials

Unless otherwise stated, analytically pure reagents that meet national standards were used for the analysis.

5.1 Carbon dioxide-free water. It is ready for use, and the conductivity is <=0.2 mS/m (25°C).

5.2 Concentrated hydrochloric acid. rho(HCl) = 1.19 g/ml.

5.3 n-butanol. phi (C4H9OH) >= 99.0%.

5.4 Ethanol. phi(C2H5OH) = 95%.

5.5 Oxalic acid (H2C2O4·2H2O). a reference reagent.

6 Instruments and equipment

6.1 Tube furnace. using silicon carbon tube as heating body, can heat the sample to above 900 °C, the temperature can be adjusted, the precision is 1 °C;

The high temperature zone is longer than 90 mm.

6.2 Glass Absorbent Bottle. The absorption bottle volume is 450 ml, and the diameter of the glass plate is 10 mm or more.

6.3 Magnetic stirrer. The stirring speed is about 500 r/min and it is continuously adjustable.

6.4 Ceramic boat.

6.5 Air pump.

6.6 Gas Flow Meter. A float flow meter with a needle valve with a flow range of 0 to 1.0 L/min.

6.7 Balance. Accuracy is 0.1 mg.

6.8 Oven. The temperature adjustment range is 0 ~ 250 °C.

6.9 Soil screen. 2 mm (10 mesh), 0.097 mm (160 mesh), stainless steel.

6.10 Acid burette. 50.00 ml.

6.11 Common instruments and equipment used in general laboratories.

1--air flow direction; 2--tube furnace; 3--glass plate absorption bottle; 4--magnetic stirrer; 5--exhaust pump; 6--gas flow meter

Figure 1 Schematic diagram of the tube furnace combustion and absorption device

Note. Other devices equivalent to those of Figure 1 can also be used.

7 Samples

8 Analysis steps

9 Calculation and representation of results

12 Waste treatment

Waste liquids such as waste acid and waste alkali generated by the laboratory and solid wastes should be collected regularly and entrusted to qualified units for disposal.

13 Precautions

13.1 The absorption efficiency of carbon dioxide is greatly affected by the size and distribution of the bubbles, so it is required that the glass plate absorbs the glass plate of the bottle.

The pores are small and the quality of the glass core should be checked before use. The method is as follows. pumping at a flow rate of 0.5 L/min, bubble path (foam height) is 50 ± 5 mm, the glass plate resistance is 4.7 ± 0.7 kPa, and the bubbles are uniform, without extra large bubbles. Magnetic stir Stirring speed of the mixer should be appropriate to distribute the bubbles evenly in the solution.

13.2 Before the first use of the ceramic boat, it should be placed in a small beaker, and a hydrochloric acid solution (5.6) should be added to the beaker to make it dip.

Not complete, take out after a while, drain, dry at 60~70 °C for 16 h, then put the ceramic boat into the tube furnace, adjust the furnace temperature is 900~1000 °C, and it is burned for 10 min to remove the influence of the ceramic boat material on the measurement results.