HJ 634-2012Soil. Determination of ammonium, nitrite and nitrate by extraction with potassium chloride solution-spectrophotometric methods (English PDF)

3.1 Ammonia nitrogen

The potassium chloride solution extracts ammonia nitrogen from the soil. Under alkaline conditions, the ammonia ions in the extract are stored with hypochlorite ions.

It reacts with phenol to form a blue indophenol dye with maximum absorption at 630 nm. Ammonia in a certain concentration range the nitrogen concentration and absorbance values are in accordance with Lambert-Beer's law.

3.2 Nitrite nitrogen

The nitrite nitrogen in the soil is extracted by potassium chloride solution. Under acidic conditions, the nitrite nitrogen in the extract is opposite to the sulfonamide.

A diazonium salt should be formed and coupled with N-(1-naphthyl)-ethylenediamine hydrochloride to form a red dye with a wavelength of 543 nm.

Maximum absorption. The nitrite nitrogen concentration and absorbance values are in accordance with Lambert-Beer's law over a range of concentrations.

3.3 Nitrate nitrogen

Nitrate nitrogen and nitrite nitrogen in soil are extracted by potassium chloride solution, and the extract is passed through a reduction column to reduce nitrate nitrogen.

For nitrite nitrogen, under acidic conditions, nitrite nitrogen reacts with sulfonamide to form diazonium salt, and then with N-(1-naphthyl) hydrochloride - Ethylenediamine is coupled to form a red dye with maximum absorption at a wavelength of 543 nm. Determination of nitrate nitrogen and nitrite nitrogen total the amount. The difference between the total amount of nitrate nitrogen and nitrite nitrogen and the nitrite nitrogen content is the nitrate nitrogen content.

4.1 Ammonia nitrogen

4.1.1 Concentrated sulfuric acid. rho(H2SO4) = 1.84 g/ml.

4.1.2 Sodium citrate dihydrate (C6H5Na3O7·2H2O).

4.1.3 Sodium hydroxide (NaOH).

4.1.4 Sodium dichloroisocyanurate (C3Cl2N3NaO3·H2O).

4.1.5 Potassium chloride (KCl). excellent grade pure.

4.1.6 Ammonium chloride (NH4Cl). excellent grade pure

Dry at 105 °C for 2 h.

4.1.7 Potassium chloride solution. c(KCl)=1 mol/L

Weigh 74.55 g of potassium chloride (4.1.5), dissolve it with an appropriate amount of water, transfer it to a 1000 ml volumetric flask, dilute to volume with water, and mix.

4.1.8 Ammonium chloride standard stock solution. rho(NH4Cl)=200 mg/L

Weigh 0.764 g of ammonium chloride (4.1.6), dissolve it with an appropriate amount of water, add 0.30 ml of concentrated sulfuric acid (4.1.1), and after cooling, Transfer to a 1000 ml volumetric flask, bring up to volume with water, and mix. The solution can be stored for one month at 4 ° C in the dark. Or direct purchase Buy a commercially available certified standard solution.

4.1.9 Standard use solution of ammonium chloride. rho(NH4Cl)=10.0 mg/L

Measure 5.0 ml of ammonium chloride standard stock solution (4.1.8) in a 100 ml volumetric flask, dilute to volume with water, and mix. Time is now Match.

4.1.10 Phenol solution

Weigh 70 g of phenol (C6H5OH) in 1000 ml of water. The solution is stored in a brown glass bottle at room temperature it can be stored for one year.

Note. Avoid contact with skin and clothing when formulating phenol solution.

4.1.11 Dihydrate sodium nitroprusate solution

Weigh 0.8 g of sodium nitroprusside dihydrate {Na2[Fe(CN)5NO]·2H2O} dissolved in 1000 ml of water. The solution is stored in in brown glass bottles, it can be stored for three months at room temperature.

4.1.12 Buffer solution

Weigh 280 g of sodium citrate dihydrate (4.1.2) and 22.0 g of sodium hydroxide (4.1.3), dissolve in 500 ml of water, and transfer in a 1000 ml volumetric flask, make up to volume with water and mix.

4.1.13 Sodium nitroprusside-phenol developer

Measure 15 ml of sodium nitroprusside dihydrate (4.1.11) and 15 ml of phenol solution (4.1.10) and 750 ml of water, and mix.

The solution is ready for use.

4.1.14 Sodium dichloroisocyanurate color developer

Weigh 5.0 g of sodium dichloroisocyanurate (4.1.4) dissolved in 1000 ml buffer solution (4.1.12) and store at 4 °C.

One month.

4.2 Nitrite nitrogen

4.2.1 Concentrated phosphoric acid. rho(H3PO4)=1.71 g/ml.

4.2.2 Potassium chloride (KCl). excellent grade pure.

4.2.3 Sodium nitrite (NaNO2). excellent grade pure

Dry in a desiccator for 24 h.

4.2.4 Potassium chloride solution. c(KCl)=1 mol/L

Same as 4.1.7.

4.2.5 Standard stock solution of nitrite nitrogen. rho(NO2-N)=1000 mg/L

4.926 g of sodium nitrite (4.2.3) was weighed, dissolved in an appropriate amount of water, transferred to a 1000 ml volumetric flask, and made up to volume with water.

uniform. The solution is stored in a polyethylene plastic bottle and can be stored for six months at 4 °C. Or buy a commercially available certified standard solution directly.

4.2.6 Nitrite nitrogen standard use solution I. rho(NO2-N)=100 mg/L

Measure 10.0 ml of nitrite nitrogen standard stock solution (4.2.5) in a 100 ml volumetric flask, dilute to volume with water, and mix. use Now available.

4.2.7 Nitrite nitrogen standard use liquid II. rho(NO2-N)=10.0 mg/L

Measure 10.0 ml of nitrite nitrogen standard solution I (4.2.6) in a 100 ml volumetric flask, dilute to volume with water, and mix.

Available when used.

4.2.8 Sulfonamide solution (C6H8N2O2S)

Add 600 ml of water to a 1000 ml volumetric flask, then add 200 ml of concentrated phosphoric acid (4.2.1), then add 80 g of sulfonamide.

Make up to volume with water and mix. The solution can be stored for one year at 4 °C.

4.2.9 Hydrochloric acid N-(1-naphthyl)-ethylenediamine solution

Weigh 0.40 g of N-(1-naphthyl)-ethylenediamine (C12H14N2·2HCl) dissolved in 100 ml of water. Store at 4 ° C, Stop using the solution as it darkens.

4.2.10 Chromogenic agent

Separate 20 ml of sulfonamide solution (4.2.8), 20 ml of N-(1-naphthyl)-ethylenediamine hydrochloride solution (4.2.9), 20 ml Concentrated phosphoric acid (4.2.1) was mixed in a 100 ml brown reagent bottle. Store at 4 ° C and stop using when the solution turns black.

4.3 Nitrate Nitrogen

4.3.1 Concentrated phosphoric acid. rho(H3PO4)=1.71 g/ml.

4.3.2 Concentrated hydrochloric acid. rho(HCl) = 1.12 g/ml.

4.3.3 Cadmium powder. Particle size 0.3 mm~0.8 mm.

4.3.4 Potassium chloride (KCl). excellent grade pure.

4.3.5 Sodium nitrate (NaNO3). excellent grade pure

Dry in a desiccator for 24 h.

4.3.6 Sodium nitrite (NaNO2). excellent grade pure

Same as 4.2.3.

4.3.7 Ammonium chloride (NH4Cl).

4.3.8 Copper sulfate (CuSO4.5H2O).

4.3.9 Ammonia water (NH4OH). excellent grade pure.

4.3.10 Potassium chloride solution. c(KCl)=1 mol/L

Same as 4.1.7.

4.3.11 Standard stock solution of nitrate nitrogen. rho(NO3-N)=1000 mg/L

Weigh 6.068 g of sodium nitrate (4.3.5), dissolve it with a proper amount of water, transfer to a 1000 ml volumetric flask, dilute to volume with water, and mix.

The solution was stored in a polyethylene plastic bottle and stored for six months at 4 °C. Or buy a commercially available certified standard solution directly.

4.3.12 Nitrate nitrogen standard use solution I. rho(NO3-N)=100 mg/L

Measure 10.0 ml of nitrate standard stock solution (4.3.11) in a 100 ml volumetric flask, dilute to volume with water, and mix. use Now available.

4.3.13 Nitrate nitrogen standard use liquid II. rho(NO3-N)=10.0 mg/L

Measure 10.0 ml of nitrate nitrogen standard solution I (4.3.12) in a 100 ml volumetric flask, dilute to volume with water, and mix.

Available when used.

4.3.14 Nitrate nitrogen standard use solution III. rho(NO3-N)=6.0 mg/L

Measure 6.0 ml of standard use solution I (4.3.12) in a 100 ml volumetric flask, dilute to volume with water, and mix. Available when used.

4.3.15 Nitrite nitrogen standard stock solution. rho(NO2-N)=1000 mg/L

Same as 4.2.5.

4.3.16 Nitrite nitrogen standard intermediate solution. rho(NO2-N)=100 mg/L

Same as 4.2.6.

4.3.17 Nitrite nitrogen standard use solution III. rho(NO2-N)=6.0 mg/L

Measure 6.0 ml of nitrite nitrogen standard intermediate solution (4.3.16) in a 100 ml volumetric flask, dilute to volume with water, and mix. use Now available.

4.3.18 Ammonia solution. (1+3).

4.3.19 Ammonium chloride buffer solution stock solution. rho(NH4Cl)=100 g/L

Dissolve 100 g of ammonium chloride (4.3.7) in a 1000 ml volumetric flask, add about 800 ml of water, and use an aqueous ammonia solution (4.3.18).

Adjust the pH value to 8.7~8.8, make up to volume with water, and mix.

4.3.20 Ammonium chloride buffer solution. rho(NH4Cl)=10 g/L

Measure 100 ml of ammonium chloride buffer solution (4.3.19) in a 1000 ml volumetric flask, dilute to volume with water, and mix.

4.3.21 Sulfonamide solution

Same as 4.2.8.

4.3.22 Hydrochloric acid N-(1-naphthyl)-ethylenediamine solution

Same as 4.2.9.

4.3.23 Chromogenic agent

Same as 4.2.10.

6.1 Sample collection

Samples were collected in accordance with the relevant regulations of HJ/T 166.

6.2 Preservation of samples

Samples should be transported and stored at 4 °C after collection and analyzed within 3 days. Otherwise, it should be -20 °C (deep cold Stored under freezing), the nitrate nitrogen and ammonia nitrogen in the sample can be stored for several weeks.

When determining the content of deep frozen nitrate nitrogen and ammonia nitrogen, the temperature and time of thawing should be controlled. Thaw at room temperature when the sample is thawed, homogenized and extracted within 4 h, if it is thawed at 4 °C, the thawing time should not exceed 48 h.

Note 1. In order to shorten the thawing time of the sample, it should be broken into small particles before the sample is frozen.

6.3 Preparation of samples

Remove the debris from the collected soil samples, mix by hand or instrument, and pass through the sample sieve. Wear rubber when mixing by hand Rubber gloves. After sieving, the sample is divided into two parts, one part is used to determine the dry matter content. For the determination method, see HJ 613; another part it is used to determine the content of the component to be tested.

6.4 Preparation of samples

Weigh 40.0 g of sample (6.3), put it into a 500 ml polyethylene bottle, and add 200 ml of potassium chloride solution (4.1.7).

The shock was extracted in a constant temperature water bath shaker at 20±2 °C for 1 h. Transfer about 60 ml of the extract to a 100 ml polyethylene centrifuge tube.

Centrifuge at 3000 r/min for 10 min. Then transfer about 50 ml of the supernatant to a 100 ml colorimetric tube.

Prepare the sample and test it.

Note 2. The extract can also be prepared by standing at 4 ° C for 4 h instead of centrifugation.

6.5 Preparation of Blank Samples

Add 200 ml of potassium chloride solution to a 500 ml polyethylene bottle and prepare according to the same procedure as preparation of sample (6.4).

Blank sample.

Note 3. The sample needs to be analyzed within one day, otherwise it should be stored at 4 °C for less than one week.

7.1 Ammonia nitrogen

7.1.1 Calibration

Measure 0, 0.10, 0.20, 0.50, 1.00, 2.00, 3.50 ml of ammonium chloride standard use solution (4.1.9) in a group Prepare a standard series by adding water to 10.0 ml in a 100 ml plug colorimetric tube. The ammonia nitrogen content is 0, 1.0, 2.0, 5.0, respectively.

10.0, 20.0, 35.0 µg.

Add 40 ml of sodium nitroprusside-phenol developer (4.1.13) to the standard series, mix well and let stand for 15 min. Of course After adding 1.00 ml of sodium dichloroisocyanurate coloring agent (4.1.14), mix thoroughly, at least 15 ° C ~ 35 ° C conditions Allow to stand for 5 h. The absorbance was measured at 630 nm with water as a reference. Taking the corrected absorbance of zero concentration as a vertical sitting the ammonia nitrogen content (µg) is plotted on the abscissa and a calibration curve is drawn.

7.1.2 Determination

Measure 10.0 ml of sample (6.4) to 100 ml with a colorimetric tube and measure according to the calibration curve (7.1.1) the amount of absorbance.

Note 4. When the ammonia nitrogen concentration in the sample exceeds the highest point of the calibration curve, the sample is diluted with potassium chloride solution (4.1.7) and re-measured.

7.1.3 Blank test

Measure 10.0 ml blank sample (6.5) to 100 ml with a colorimetric tube and follow the calibration curve (7.1.1).

The absorbance is measured.

7.2 Nitrite nitrogen

7.2.1 Calibration

Measure the 0, 1.00, 5.00 ml nitrite nitrogen standard solution II (4.2.7) and 1.00, 3.00, 6.00 ml Nitrite nitrogen standard use liquid I (4.2.6) in a set of 100 ml volumetric flask, dilute with water to the mark, mix, prepare the standard the quasi-series has nitrite nitrogen contents of 0, 10.0, 50.0, 100, 300, and 600 µg, respectively.

Measure 1.00 ml of the above standard series in a set of 25ml plug colorimetric tubes, add 20 ml of water, and shake well. To each Add 0.20 ml of color developer (4.2.10) to the colorimetric tube, mix well, let stand for 60 min to 90 min, and develop color at room temperature.

The absorbance was measured at a wavelength of 543 nm with water as a reference. To subtract the zero concentration of the corrected absorbance as the ordinate, nitrous oxide the acid nitrogen content (µg) is plotted on the abscissa and a calibration curve is drawn.

7.2.2 Determination

Measure the absorbance according to the calibration curve (7.2.1) colorimetric tube by taking 1.00ml sample (6.4) to 25 ml colorimetric tube.

degree.

Note 5. When the nitrite nitrogen content in the sample exceeds the highest point of the calibration curve, the sample is diluted with potassium chloride solution (4.1.7), and the weight is heavy.

New measurement.

7.2.3 Blank test

Measure 1.00ml blank sample (6.5) to 25 ml colorimetric tube and measure according to calibration curve (7.2.1) colorimetric step Absorbance.

7.3 Nitrate Nitrogen

7.3.1 Preparation of the reduction column before use

Open the piston and let the ammonium chloride buffer solution flow out of the reduction column. If necessary, wash off the salt formed on the surface with water.

Then use 20ml ammonium chloride buffer solution (4.3.20), 20ml ammonium chloride buffer solution (4.3.19) and 20 ml of ammonium chloride buffer solution was filtered through the reduction column (4.3.20) and used.

7.3.2 Calibration

Measure 0, 1.00, 5.00 ml of nitrate nitrogen standard use solution II (4.3.13) and 1.00, 3.00, 6.00 ml of nitrate the standard of acid nitrogen is prepared by using liquid I (4.3.12) in a set of 100ml volumetric flasks, diluted with water to the mark, and mixed.

In the series, the nitrate nitrogen contents were 0, 10.0, 50.0, 100, 300, and 600 µg, respectively.

Close the piston and measure 1.00 ml of the calibration series in the reduction column. Add 10ml ammonium chloride buffer to the reduction column Solution (4.3.20), then open the piston, pass the reduction column at a flow rate of 1 ml/min, and use a 50 ml plug colorimetric tube Collect the eluent. When the liquid level reaches the top cotton, add 20ml ammonium chloride buffer solution (4.3.20), collection house.

There is effluent and remove the colorimetric tube. Finally, the reduction column was washed with 10 ml of ammonium chloride buffer solution (4.3.20).

To the above colorimetric tube, 0.20 ml of a color developing agent (4.3.23) was added, mixed well, and allowed to stand at room temperature for 60 minutes to 90 minutes.

The absorbance was measured at a wavelength of 543 nm with water as a reference. To subtract the zero concentration of the corrected absorbance as the ordinate, nitric acid the salt nitrogen content (µg) is plotted on the abscissa and a calibration curve is drawn.

7.3.3 Determination

Measure 1.00 ml of the sample (6.4) into the reduction column and measure the absorbance according to the calibration curve (7.3.2).

Note. When the total amount of nitrate nitrogen and nitrite nitrogen in the sample exceeds the highest point of the calibration curve, dilute with potassium chloride solution (4.1.7).

Sample, re-measure.

7.3.4 Blank test

Measure 1.00 ml of the blank sample (6.5) into the reduction column and measure the absorbance according to the calibration curve (7.3.2).

8.1 Calculation of results

8.1.1 Ammonia nitrogen

The ammonia nitrogen content omega (mg/kg) in the sample was calculated according to the formula (1).

Mm ··-= 01omega (1)

omega - the content of ammonia nitrogen in the sample, mg / kg;

1m -- the content of ammonia nitrogen in the sample obtained from the calibration curve, µg;

0m -- the content of ammonia nitrogen in the blank sample found from the calibration curve, µg;

V--the sample volume at the time of measurement, 10.0 ml;

f -- the dilution factor of the sample;

R--sample volume (including the volume of the extract and the volume of water in the soil) and the ratio of the dry soil, ml / g;

Calculate according to formula (2).

Dms

OHdmsES

dwmV

-·+= ]/)1([ 2 (2)

ESV - volume of extract, 200ml;

Sm -- the amount of sample, 40.0g;

OHd 2 - water density, 1.0 g / ml;

Dmw -- the dry matter content of the soil, %.

8.1.2 Nitrite nitrogen

The nitrite nitrogen content in the sample is omega (mg/kg), which is calculated according to formula (3).

Mm ··-= 01omega (3)

omega - the content of nitrite nitrogen in the sample, mg / kg;

1m -- the content of nitrite nitrogen in the sample obtained from the calibration curve, µg;

0m -- the content of nitrite nitrogen in the blank sample found from the calibration curve, µg;

V--the sample volume at the time of measurement, 1.00 ml;

f -- the dilution factor of the sample;

R--sample volume (including the volume of the extract and the volume of water in the soil) and the ratio of the dry soil, ml / g;

Calculate according to formula (2).

8.1.3 Total nitrate nitrogen and nitrite nitrogen

The content of nitrate nitrogen and nitrite nitrogen in the sample is omega (mg/kg), which is calculated according to formula (4).

Mm ··-= 01omega (4)

omega - the total amount of nitrate nitrogen and nitrite nitrogen in the sample, mg / kg;

1m -- the content of nitrate nitrogen and nitrite nitrogen in the sample obtained from the calibration curve, µg;

0m -- the content of nitrate nitrogen and nitrite nitrogen in the blank sample found from the calibration curve, µg;

V--the sample volume at the time of measurement, 1.00 ml;

f -- the dilution factor of the sample;

R--sample volume (including the volume of the extract and the volume of water in the soil) and the ratio of the dry soil, ml / g;

Calculate according to formula (2).

8.1.4 Nitrate nitrogen

Nitrate nitrogen content in the sample Nitrate nitrogen omega (mg/kg), calculated according to formula (5).

Nitrate nitrogen omega = total nitrate nitrogen and nitrite nitrogen omega - nitrate nitrogen sub-omega (5)

8.2 Results representation

When the measurement result is less than 1mg/kg, keep two decimal places; when the measurement result is greater than or equal to 1mg/kg, keep three A valid number.

9.1 Ammonia nitrogen

Soil samples with ammonia nitrogen contents of 0.73 mg/kg, 1.59 mg/kg, and 5.69 mg/kg were tested in the laboratory.

The relative standard deviations were 8.41%, 4.77%, and 4.63%, respectively.

The soil samples with ammonia nitrogen content of 1.62 mg/kg were spiked and analyzed in the laboratory. The scalar amount was 40µg.

And 100µg; the soil samples with ammonia nitrogen content of 5.76 mg/kg were spiked and analyzed, and the spiked amount was 200µg.

The recoveries of spiked samples were 80.9%~105%.

9.2 Nitrite nitrogen

In the laboratory, soil samples with nitrite nitrogen contents of 2.46 mg/kg, 4.09 mg/kg, and 8.64 mg/kg were taken.

The relative standard deviations were 5.72%, 1.66%, and 1.25%, respectively.

The actual soil samples with nitrite content of 2.46 mg/kg were spiked and analyzed in the laboratory. The scalar quantity was 400µg; the actual soil samples with nitrite nitr...