Some standard content:
National Standard of the People's Republic of China
Method for the determination of available boron in soil
1 Subject content and scope of application
This standard specifies the curcumin absorbance method for determining available boron in soil. This standard is applicable to the determination of available boron in various soils. 2 Principle of determination
GB 12298-90
The boron extracted from soil by hot water has a high correlation with the response of crops to boron. Boron in the extract reacts with curcumin in the presence of oxalic acid and forms a rose-red complex after dehydration. The absorbance is determined after dissolving it in ethanol. The red complex solution is in the range of 0.0025-0.05μgB/mL, which conforms to the Lambert-Beer law. 3 Main instruments and equipment
The glassware used in the test should be soaked in 1+3 hydrochloric acid for 2-4 hours before use, then rinsed with water and dried. 3.1 Soil sample sieve (nylon sieve) 2.0mm square hole sieve. 3.2 Analytical balance, sensitivity 0.0001, 0.001g. 3.3 Spectrophotometer.
3.4 Electric constant temperature water bath. Www.bzxZ.net
3.5 Thermostatic electric stove or alcohol lamp.
3.6 Conical flask 250mL (quartz or low-boron glass). 3.7 Reflux condenser (quartz or low-boron glass). Evaporating dish 50mL (quartz or polyethylene products). 3.8
Graduated pipette 1.00, 5.00, 20.0mL. 3.9
3.10 Polyethylene bottle 30, 60, 1000mL.
Medium speed filter paper 11cm.
4 Reagents
All water used in the test is deionized water or double distilled water from a quartz distiller. 4.195% ethanol (GB679 analytical grade).
4.2 Magnesium sulfate solution: 10.00g MgSO47H20 (GB671, analytical grade) dissolved in 100mL water. 4.3 Curcumin-oxalic acid solution: Weigh 0.040g curcumin and 5.00g oxalic acid (HG3-988, high-grade pure) and dissolve in 100mL 95% ethanol (4.1), stir thoroughly to dissolve completely, and store in a brown glass bottle. This solution should be prepared one day before use, sealed and stored in a refrigerator for one week.
4.4 Boron standard solution: Weigh 0.5720g dry boric acid (GB628, high-grade pure) and dissolve in water, dilute to 1L, and store in a plastic bottle. This solution is a 100μg/mL boron stock solution. Dilute the boron stock solution 10 times to obtain the 10μg/mL boron standard working solution, approved by the State Administration of Technical Supervision on March 29, 1990 1.48
Implementation on December 1, 1990
5 Determination steps
5.1 Extraction of available boron in soil
GB 12298-90
Weigh 10.00g of air-dried soil sample that has passed through a 2.0mm sieve into a 250mL conical flask, add 20.0mL of water at a soil-water ratio of 1:2, connect a condenser, boil over low heat for 5min, remove the heat source immediately, continue to reflux and condense for 5min (accurate timing), remove the conical flask, add 2 drops of magnesium sulfate solution (4.2), shake well and filter immediately, pour the suspension in the flask onto the filter paper (3.11) at once, and place the filter paper in a polyethylene bottle. Perform two parallel determinations on the same sample.
Meanwhile, prepare a blank solution with water according to the above extraction steps. 5.2 Colorimetric determination
Pipette 1.00mL of the filtrate into 50mL evaporator III (3.8), add 4.00mL of curcumin-oxalic acid solution (4.3), evaporate to dryness in a constant temperature water bath at 55±3℃, start timing from the time it turns rose red and continue baking for 15min, remove the evaporator and cool to room temperature, add 20.0mL of 95% ethanol (4.1), scrub the dish wall with a rubber dust broom to completely dissolve the contents, filter with medium-speed filter paper into a stoppered container (this solution should not be left for more than 3h), use 95% ethanol (4.1) as the reference solution, and measure the absorbance at a wavelength of 550nm in a spectrophotometer. Use a 1cm optical path colorimetric dish.
Note: (①If the nitrate content in the soil exceeds 20ug/g, it will interfere with the color development. A certain amount of filtrate must be taken and added with saturated calcium hydroxide solution. After evaporating it on a water bath, the nitrate is burned to destroy the nitrate. Then, 0.1mol/L hydrochloric acid is used to dissolve the residue and then color development is performed. ②The color development conditions of the test solution, blank solution and standard series solution (such as temperature, type and volume of container, and evaporation rate) must be strictly consistent.
5.3 Working curve drawing
Use 10μg/mL boron working solution (4.4) according to 0, 0.10.2, 0.4, 0. 6, 0.8, 1.0ug/mL boron concentrations are prepared into a series of boron standard solutions. 1.00mL is taken respectively and the absorbance is determined according to 5.2 for color development and a working curve is drawn. 6 Calculation of analysis results
After subtracting the blank absorbance from the sample absorbance, the boron concentration is obtained from the working curve. The effective boron content of the soil is expressed in mg/kg and is calculated as follows: Effective boron content of soil = 2c
The boron concentration is obtained from the sample absorbance from the working curve, mg/kg; where: c—
2—water-soil ratio.
Note: If the effective boron content of the soil is high, the boron content in the test solution exceeds 1 ug/mL, the filtrate should be diluted for color development. Multiply by the dilution factor when calculating. 7 Allowable difference of parallel results
The results of two parallel determinations are expressed as the arithmetic mean, and two decimal places are retained. The allowable difference of the results of two parallel samples: when the effective boron in the soil is less than 0.2mg/kg boron, it is 0.03mg/kg; when the effective boron is 0.2~0.5mg/kg, it is 0.05mg/kg; when the effective boron is greater than 0.5mg/kg, the difference does not exceed 0.06mg/kg. Additional notes:
This standard was proposed by the Ministry of Agriculture, Animal Husbandry and Fisheries of the People's Republic of China. This standard was drafted by the Analysis and Testing Center of the Chinese Academy of Agricultural Sciences. The main drafters of this standard are Mu Xin, Zhu Ke, Wang Zhirong and Li Yufang. 149
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