HJ 695-2014Soil. Determination of organic carbon. Combustion oxidation nondispersive infrared absorption method (English PDF)

5.4 Sucrose solution. rho (organic carbon, C) = 10.0 g/L

Weigh 2.375 g of sucrose (5.3) which has been dried at 104 °C for 2 h, dissolved in an appropriate amount of water (5.1), and transferred to a capacity of 100 ml.

In the bottle, dilute to the mark with water (5.1) and mix. Stored at room temperature, valid for two weeks.

5.5 Phosphoric acid solution. phi(H3PO4)= 5 %

Measure 59 ml of concentrated phosphoric acid (5.2) dissolved in 700 ml of water (5.1), cool to room temperature, and dilute with water (5.1) until 1000ml. Stored at room temperature, valid for two weeks.

5.6 Carrier gas. nitrogen, purity 99.99%.

5.7 Gas. oxygen, purity 99.99%.

7.1 Sample collection and preservation

The collection and storage of soil samples is carried out in accordance with the relevant provisions of HJ/T 166.

7.2 Preparation of samples

Place the soil sample in the air-drying tray and spread it into a thin layer of 2 ~ 3 cm thick, first removing the residues such as plants, insects, stones, etc.

Crush the clods with a hammer or a porcelain abrasive rod, flip it several times a day, and air dry.

Mix the air-dried soil thoroughly, use the quadruple method, take two parts, one part is retained, one part is ground to all over 2 mm (10 Mesh) soil sieve. Take 10 ~ 20 g of the sieved soil sample and grind it to the entire 0.097 mm (160 mesh) soil sieve.

Load into a brown stoppered glass bottle for testing.

7.3 Determination of dry matter content

The air-dried soil samples after 2 mm (10 mesh) sieve were accurately weighed, and the dry matter content of the soil was determined by reference to HJ 613.

8.1 Instrument Commissioning

Set the condition parameters and debug according to the instructions of the total organic carbon analyzer.

8.2 Drawing of the calibration curve

Use a pipette to accurately measure 0.0, 0.5, 1.0, 2.5, 5.0, 10.0 ml sucrose solution (5.4) in 10.0 ml in the measuring flask, dilute to the mark with water (5.1) and prepare the concentrations of 0.0, 0.5, 1.0, 2.5, 5.0, 10.0 g/L, respectively.

Calibration series. Use a micro-syringe (6.4) to take.200 µl of the calibration series in a quartz cup with a small amount of glass wool on the pad.

The organic carbon content is 0.00, 0.10, 0.20, 0.50, 1.0, and 2.0 mg, respectively, and the quartz cup is placed in the total organic carbon analyzer (6.1).

The response value of the standard series is determined from low concentration to high concentration in turn, and the organic carbon content (mg) is plotted on the abscissa.

The value should be the ordinate and the calibration curve should be drawn.

8.3 Determination

Weigh 0.05g (7.2) of the sample to the nearest 0.0001 g, put it into a quartz cup with a small amount of glass wool on the pad, and slowly add it.

Phosphoric acid solution (5.5), no bubbles appeared in the sample. The quartz cup was placed in a total organic carbon analyzer (6.1) and the response was measured.

Note 2. When the sample concentration is high, the sample size can be appropriately reduced, but should not be less than 0.01g.

8.4 Blank test

Replace the sample with.200 µl of water (5.1) and measure according to step (8.3).

9.1 Calculation of results

The organic carbon content ocomega (in terms of carbon, mass fraction, %) in the soil is calculated according to the formulas (1) and (2).

Dmwmm ×= (1)

aAA

Ocomega

In the formula.

M1--the mass of dry matter in the sample, g;

M--sample sample amount, g;

Dmw -- dry matter content (mass fraction) of soil samples, %;

Ocomega - the content of organic carbon in soil samples (in terms of carbon, mass fraction), %;

A -- sample response value;

0A - blank sample response value;

a -- the intercept of the calibration curve;

b -- The slope of the calibration curve.

9.2 Results representation

When the measurement result is 1%, the relative deviation of the parallel sample measurement results is <=10.0%.

11.2 When testing each batch of samples, a certified standard sample shall be analyzed and its measured value shall be within the guaranteed value range.

11.3 The correlation coefficient of the calibration curve should be greater than or equal to 0.995.

11.4 Each batch of samples shall be tested with a calibration sample at the middle of the calibration curve. The measured values of the calibration samples are relative to the calibration curve.

The relative error of the point concentration should not exceed 10%.