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determination of phosphorus and inorganic phosphorus in phosphate ester
Release Date:2018-9-18 Source:xiashundong Views:522

Phosphates are anionic surfactants. It has many functions, such as moistening, defoaming, leveling dyeing, antistatic and so on. It is widely used in textile processing, public cleaning, leather pulp, emulsion polymerization, metal processing and so on. There are more than 50 kinds of phosphate esters, including alkyl, alkyl ether, nonylphenol polyoxyethylene ether phosphate esters and their potassium, sodium and ammonium salts. The binding phosphorus and inorganic phosphorus in phosphate surfactant have great influence on its quality. The analysis and determination of phosphorus and inorganic phosphorus in phosphate surfactant were discussed. Through the decomposition of samples, the quality of phosphorus and inorganic phosphorus was determined by ammonium vanadium molybdate method. The method is simple and easy to operate, and the experimental results are stable. It can be used as a plant control analysis. It has certain significance for detecting the quality of phosphate surfactant.

1 Determination of phosphorus

First, the quality of total phosphorus was measured, then the quality of inorganic phosphorus was measured. The total phosphorus minus inorganic phosphorus was equal to the quality of bound phosphorus.

1.1 experiment

1.1.1 principle

The sample was decomposed into orthophosphate by sulfuric acid, nitric acid and perchloric acid. The orthophosphate, vanadate and molybdate formed yellow complex in acidic solution. The quality of phosphorus was determined by absorption value of yellow complex.

1.1.2 reagent and instrument

Ammonium molybdate aqueous solution: dissolve 40 g ammonium molybdate tetrahydrate in 500 mL volumetric flask, add 400 mL hot distillation water solution, cooling to room temperature. Diluted with distilled water to scale, this solution is A solution.

Ammonium Vanadate Solution: Carefully pour 200 mL nitric acid into 200 mL distilled water, then add 20 g ammonium vanadate to warm, cool and dilute to 500 mL volumetric flask, the solution is stable, this solution is B solution.

Standard Phosphate Solution (KH2PO4): accurately weigh potassium dihydrogen phosphate 1.1g (+0.1mg) in distilled water, which must be dried overnight in an oven at 105 C to the Pharmacopoeia standard) and dissolved in distilled water, diluted to 1L volumetric flask.

Apparatus: type 721 spectrophotometer.

1. 1.3 operation steps

Operation: accurately weigh 0.10 ~ 0.15 g sample in 250 mL conical bottle, add 6 mL concentrated H2SO4, slowly heat in the electric furnace until dissolved. When blackened, boil for 10 minutes, add 4 mLn (HNO3):n (HClO4)=3:1 aqueous solution, boil to colorless solution, cool, add 30 mL distilled water, add zeolite, continue to boil for 4 minutes, cool and move to 500 mL volumetric flask, dilute to the scale. Move 50 mL to 100 mL volumetric flask, add 2-3 drops of 0.1% phenolphthalein indicator solution, mix it with 5 mol/L NaOH solution to pink, add 5 mL mixed reagent (A solution and B solution, etc.), dilute it with distilled water to the scale, store it for 20 minutes, measure the absorbance at 460 nm, check the quality of phosphorus by standard curve.

Drawing standard curve: Add 0.0, 1.0, 2.0, 3.0, 4.0, 5.0 mL standard phosphate solution and 5 mL mixed reagent into 100 mL volumetric bottle, dilute it to 100 mL with distilled water, measure absorbance at 460 nm of 721 spectrophotometer with 1 cm colorimetric dish, and do a blank experiment at the same time. Draw standard curve.

Calculation: total phosphorus: omega (P) =V * 0.2279 * 10-2/m * 100%

Omega (phosphorus) = omega (total phosphorus) - omega (inorganic phosphorus)

Formula: V is the volume (mL) of phosphorus obtained from the standard curve, 02279 *10-2 is the mass (g) of phosphorus corresponding to each milliliter of standard solution, and M is the mass (g) of the sample.

1.2 results and discussion

1.2.1 maximum wavelength selection

When the standard sample 3.0mL for phosphorus was measured on the instrument, the wavelength and sensitivity of 1cm were selected. Wavelength: 460nm; sensitivity: 2 files.

1. 2.2 acidity selection

After the decomposition of the sample, the acidity has a great influence on the color reaction and whether acid is added after neutralization.

Comparison of 1.2.3 chromogenic time

5mL standard phosphate solution was used to make the color time test.

The color time has little effect on absorbance. After placing 48h, the absorbance is not changed. The color time is 15~20min.

2 Determination of inorganic phosphorus

2.1 experiment

2.1.1 principle

Orthophosphate forms yellow complex with vanadate and molybdate in acidic solution. The quality of phosphorus is determined by absorption value of yellow complex.

H3PO4+NH4VO3+16 (NH4) 2MoO4+29HNO3=

(NH4) 3PO4. NH4VO3. 16MoO3+29NH4NO3+16H2O

2.1.2 reagent and instrument

The same as total phosphorus determination.

2.1.3 operation steps

Operation: accurately weigh 0.1-0.2 g sample, place it in centrifugal tube, add hot anhydrous ethanol to 2/3 of the centrifugal tube, stir evenly, separate with centrifuge, pour out the clear liquid, repeat. Add distilled water to the sediment, dissolve the sediment, add 50 mL distilled water, 3 mL nitric acid, boil for 10 minutes, cool, transfer to 250 mL volumetric flask, add 2-3 drops of phenolphthalein solution, drop to pink with 5 mol/L NaOH solution, then add 5 mL mixed reagent (A, B mixed with volume), dilute it to the scale with distilled water, and use spectrophotometer. Measure absorbance at 460nm.

The standard curve is drawn: the same as total phosphorus.

Calculation: inorganic phosphorus = V *0.2279 *10-2 *2.5/m *100% formula: V - Volume of phosphorus (mL) from the phosphate standard curve, 0.2279 *10-2 - mass (g) of phosphorus per milliliter of standard solution, m - mass (g) of sample.

2.2 results and discussion

Selection of 2.2.1 separation conditions

Whether the separation is complete or not has great influence on the analytical results of inorganic phosphorus. It is known that organic phosphorus is soluble in alcohol, while inorganic phosphorus is insoluble, and inorganic phosphorus is separated from organic phosphorus by ethanol. In addition, the amount of sample is also an influence on the effect of separation. It is advisable to select the sample weight in 0.1~0.2g. When washing and washing, we should pay attention to whether washing is thorough. When water is dissolved, if centrifugal effect is not good, it should be centrifuged.

2.2.2 polyphosphate decomposition

Because inorganic phosphorus compounds also have polyphosphoric acid, a small amount of nitric acid is added to boil before the determination to ensure the accuracy of the determination results.

3 conclusion

The method can be used to determine the quality of inorganic phosphorus and bound phosphorus in phosphate. The results are accurate and simple, and have been applied to the analysis of actual samples.

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