Shen ChangHong The total phosphorus is determined by changing various forms of phosphorus into orthophosphate after digestion of water sample. It is measured by mg of phosphorus per litre of water sample. According to the GB / t10647 feed industry term total phosphorus (TP), the total amount of phosphorus existing in inorganic and organic state in feed.
1、 Determination of total phosphorus in water by ammonium molybdate method
Under neutral condition, potassium persulfate was used to digest the water sample and convert the phosphorus contained into orthophosphate. In the acid medium, orthophosphate reacts with ammonium molybdate to form phosphomolybdic heteropoly acid in the presence of antimony salt, which is immediately reduced by ascorbic acid to form a blue complex, and the color is compared at the wavelength of 700nm.
2、 How to use reagents in total phosphorus analyzer?
Unless otherwise specified, all reagents of analytical purity or above shall be distilled water
1. Reagent 1: take the whole bottle of total phosphorus "reagent 1" and put it into a 250ml beaker, add about 80ml of distilled water, stir until it is completely dissolved, use distilled water in a 100ml volumetric flask to fix the volume to the scale line, store it in a reagent bottle and refrigerate it in a refrigerator at 2-8 ℃, with a shelf life of 1 month.
2. Reagent 2: Take 1 small package of total phosphorus "reagent 2" in a small beaker, transfer 5.0ml distilled water with a pipette for dissolution, refrigerate in a refrigerator at 2-8 ℃, if the solution changes color, it can not be used again, and the general shelf life is 2 weeks.
3. Reagent 3: direct use, stored in refrigerator at 2-8 ℃.
4. Standard solution (1000mg / L): accurately weigh 2.1970g of potassium dihydrogen phosphate dried at 110 ℃ for 2h, dissolve it in distilled water, use a 500ml volumetric flask to fix the volume to the mark line, and shake it for standby.
5. Use solution (2.0mg / L): transfer 1.0ml of 1000mg / L standard solution into a 500ml volumetric flask, use distilled water to fix the volume to the scale line, and shake well for standby.
3、 Precautions of total phosphorus tester by ammonium molybdate method
1. During the experiment, the glassware and colorimetric tube used shall be cleaned with sulfuric acid if necessary.
2. Before the prepared sample is tested on the machine, ensure that the outer wall of the colorimetric tube is wiped clean without water drops or hand marks.
3. When analyzing the water sample, shake the water sample evenly and then take the sample. The water sample cannot be filtered.
