Introduction to the Working Principle of On-line Analyzer for Determination of Total Phosphorus

What is total phosphorus? The phosphorus in the water may be elemental phosphorus. orthophosphate. Condensed phosphate. Pyrophosphate. Some phosphates and organophosphates. The main source of total phosphorus is domestic sewage. fertilizer. Organophosphorus pesticides and phosphate cleaners used in modern detergents. Total phosphorus is measured after digestion of the water sample to convert all forms of phosphorus to orthophosphate and is expressed in milligrams of phosphorus per liter of water sample. 1. Method principle. Under acidic conditions, orthophosphate reacts with ammonium molybdate and potassium antimony tartrate to produce phosphomolybdenum heteropolyacid, which is reduced to a blue complex by a reducing agent, usually integrating phosphomolybdenum blue. The minimum detection concentration of this method is 0.01mg/L (the corresponding concentration when absorbance a=0.01); the upper limit of measurement is 0.6mg/L. It can be used for the determination of orthophosphate in surface water, domestic sewage and industrial wastewater such as daily chemicals, phosphate fertilizers, phosphating treatment of processed metals, pesticides, iron and steel, and coking. 2. Instruments. Spectrophotometer. 3. Reagents. (1) 1+1 sulfuric acid. (2) 10% (m/V) ascorbic acid solution: dissolve 10 grams of ascorbic acid in water and dilute to 100 ml. This solution is stored in a brown glass bottle and is stable for several weeks in a cold place. If the color turns yellow, discard the reassignment. (3) Molybdate solution: dissolve 13g ammonium molybdate [(NH4)6mo7o24.4H2O] in 100ml water. Dissolve 0.35 g of antimony potassium tartrate (Sbo (C4H4·1/2H2O)) in 100 ml of water. Slowly add ammonium molybdate solution to 300ml (1+1) sulfuric acid, add antimony potassium tartrate solution, and mix well. Reagents are stored in amber glass bottles and kept in a cold place. At least 2 months. (4) Turbidity-color compensation solution: 1+1) mixed volume of sulfuric acid and 10% (m/V) ascorbic acid solution. (5) Phosphate storage solution: Potassium dihydrogen phosphate (KH2PO4) was dried at 110°C for 2 hours, then cooled in a desiccator. Weigh 0.217g, dissolve it in water, and transfer it into a 1000ml volumetric flask. Add 5ml of (1+1) sulfuric acid and dilute to the mark with water. (6) Phosphate standard solution: absorb 10.00ml of phosphate storage solution in a 250ml volumetric flask, and dilute with water to the mark. This solution contained 2.0 ug of phosphorus per milliliter. 4. Measuring steps (only take the in and out water samples as an example) (1) Take back the in and out water samples and shake them well (shake the water samples on the biochemical pool for a period of time to take the supernatant). (2) Take 3 plug-type scale tubes, add distilled water to the upper scale line in the first plug-type scale tube; add 5ml of water sample into the second plug-type scale tube, and then add distilled water to the upper scale line; Soak the plug-type graduated tube in hydrochloric acid for 2 hours, or brush it with a phosphate-free detergent. (3) After use, soak in dilute nitric acid or chromic acid lotion for a while to remove the adsorbed molybdenum blue. The working principle of the total phosphorus monitor: Under the acidic conditions of high temperature and high pressure, phosphorus compounds such as polyphosphate in water are hydrolyzed to form phosphate; for other phosphorus compounds that are difficult to oxidize, they are oxidized to phosphate by the strong oxidant sodium sulfate. Then, according to the measurement range, total phosphorus monitoring instruments include molybdenum blue method and molybdenum alum method. 1. Molybdenum blue method: Phosphate ions react in a strong acid solution containing molybdate to form a yellow phosphomolybdate complex, which is reduced to blue phosphomolybdate by ascorbic acid. Measure the absorbance of phosphomolybdate at a wavelength of 850nm, and compare it with the standard to obtain the total phosphorus content of the sample. 2. Molybdenum alum method: Phosphate ions react in a strong acid solution containing molybdenum salts to form a yellow phosphomolybdic acid complex, and alum reacts with this compound to form yellow alum phosphomolybdic acid. Measure the absorbance of alum phosphomolybdic acid at a wavelength of 430nm, and compare it with the standard to obtain the total phosphorus content of the sample. The working principle of BOQU Total Nitrogen Analyzer: The instrument uses ultraviolet spectroscopy (UV254); when organic substances containing conjugated double bonds or polycyclic aromatic hydrocarbons are dissolved in water, they will absorb ultraviolet rays. Therefore, by measuring the absorption degree of these organic substances to 254nm ultraviolet rays, the measurement results are expressed by the special absorption coefficient of SAC254 as a physical quantity to measure the total amount of organic pollutants in water. According to Beer Lambeau's law, the measurement principle is based on the absorption of ultraviolet light by unsaturated organic molecules, with a wavelength of 254nm. [C]=k log (Iin/Iout)/[C]: sample concentration; K: linear correlation coefficient between ultraviolet absorption and COD. Iin: incident light intensity / Iout: transmitted light intensity / the instrument automatically compensates for turbidity through a dual-beam system (another detector 550nm).
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