Total phosphorus detection method and matters needing attention

Determination principle of total phosphorus detection method:

Under neutral conditions, the sample is digested with potassium persulfate, and all the phosphorus contained in it is oxidized to orthophosphate. Orthophosphate reacts with ammonium molybdate in an acidic medium. After the formation of phosphomolybdenum heteropoly in the presence of antimony salt, a blue complex is formed. Place it at room temperature for 15 minutes. Use a cuvette with an optical path of 10mm or 30mm. At a wavelength of 700nm, pure water is used as a reference to measure absorbance.

Steps of detection method:

Step 1. Take 5mL of water sample into the micro-reflux tube, add 1.0ml of potassium peroxodisulfate, pay attention to wipe off the water on the outer wall of the micro-reflux tube, and then put it in the digester at 120 degrees for digestion 30 After cooling down, select the dilution factor according to the situation and transfer it into a 25ml colorimetric tube.

Step 2. Add 0.5ml of color aid and 1ml of color developer dropwise, cover tightly, and shake well to make the drug and the sample fully reflect, and let it stand for 15 minutes.

Step 3. Move the water sample to the colorimetric tube, use a 700nm wavelength light wave for detection, the reading multiplied by the dilution factor is the true value of total phosphorus.

Precautions for total phosphorus detection method:

1. Colorimetric process: select the curve (No. 0), put a blank cuvette into the colorimetric cell, close the lid and wait for the data to stabilize, press the (Set/Blank) key to display total Phosphorus 0mg/L, T u003d100%'; put the water sample cuvette into the colorimetric cell, close the lid and record the value after the reading is stable, the displayed value is the total phosphorus concentration of the water sample; if the water sample is measured after dilution, the displayed value is multiplied by the dilution The multiple is the total phosphorus concentration of the original water sample.

2. The curve (No. 0) is the factory-set curve of the instrument, which can be directly used to measure water samples. If the measurement conditions are changed and the results have a large deviation, please use this reagent and method, and then use the standard solution to calibrate the curve. , Select the calibrated curve for water sample measurement.

3. The quality of the reagent has a great influence on the determination, it is recommended to use the original reagent.

4. The waste liquid generated after the test must be stored in a centralized manner and sent to a qualified unit for processing. To avoid environmental pollution, please do not dump it at will.

5. If there is precipitation in the sample, please carefully pour the supernatant into the cuvette; each link of the water sample measurement process should be continuous. The sample should not be placed for a period of time or repeated measurement in different time periods.