Determination of Total Nitrogen, Phosphorus and Potassium Colorimetry (Rapid Measurement, Reference)
(Reference national standard: GB6432-86; GB6437-86)
First, the test solution preparation:
Weigh 0.5000 g of uniformly ground (0.5 mm) sample and put it into a 100 ml decoction tube. Add 5 ml of concentrated sulfuric acid, shake well and slowly add 2 ml of hydrogen peroxide. Shake well and put it on a small fire and heat it. Cook until white smoke (response stop violently), remove natural cooling and then add 2 ml of hydrogen peroxide, heat and cook, add 2 ml of hydrogen peroxide after cooling, and repeat until the sample liquid becomes colorless and transparent (if it is cooled, it is light yellow or Brown, still need to add hydrogen peroxide to boil), add water after cooling to 100 ml, shake.
Second, the colorimetric determination of nitrogen, phosphorus and potassium in the test liquid:
1: Nitrogen: Absorption Cook sample solution to be 5.0 ml into a 50 ml volumetric flask, dilute to volume with water, and then absorb 5 ml into a beaker, add ammonium nitrogen reagents after color comparison, the same operation Determination of soil ammonium nitrogen.
2: Phosphorus measurement: Absorption cook 1.0 ml sample solution to be measured in a 50 ml volumetric flask, add colorimetric reagents for color development, and determine the available phosphorus in the soil.
3: Potassium measurement: Absorption Cook sample solution 1.0 ml in a small beaker, add 5 ml of water, add 2 drops of thymolphthalein indicator, and add 2mol/L sodium hydroxide solution to neutral to light blue during shaking. , Heat to boil for 2 minutes to cool and transfer to a 50 ml volumetric flask.
Third, the result is calculated:
1: sample crude protein content% = color solution mg/ml count × 50ml/5ml × 100ml/0.5g × 100/106 × 6.25
2: P% = coloring solution mg/ml × 50/1 × 100ml/0.5g × 100/106
= Color solution mg/ml
3: K%=same as above = turbid liquid mg/ml
Note: The result of P, K content in feed is expressed as element P or K instead of P2O5 or K2O. Therefore, the concentration unit of the standard solution used in colorimetric comparison should also be expressed as single element P or K.
Another: If the laboratory conditional measurement using the national standard method, according to GB6432-86 Kjeldahl method to measure N; according to GB6437-86 ammonium vanadium molybdate method (explicit yellow) colorimetric measurement P, feed generally do not measure potassium, so also There is no national standard method for measuring feed potassium.
The above is for reference only: Institute of Soil Fertility, Chinese Academy of Agricultural Sciences, and Zhu Haizhou, member of the National Agricultural Analysis Method Standardization Technical Committee.
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