Determination of binding phosphorus and inorganic phosphorus in phosphate ester

Phosphate esters are anionic surfactants. It has many functions such as wetting, defoaming, levelling, antistatic, etc. It is widely used in textile processing, public cleaning, leather pulp, emulsion polymerization, metal processing and so on. There are more than 50 varieties of phosphate salts, and the types of phosphate esters are alkyl, alkyl ether, nonylphenol polyoxyethylene ether phosphate and potassium, sodium and ammonium salts. The binding phosphorus and inorganic phosphorus in phosphate ester surfactants have great influence on its quality. The analysis and determination of binding phosphorus and inorganic phosphorus in phosphate ester surfactants were discussed. The quality of bonded phosphorus and inorganic phosphorus was determined by ammonium vanadomolybdate method. The method is simple and easy to operate, the experimental results are stable, and it can be used as the control analysis in the factory. It has a certain significance for detecting the quality of phosphate ester surfactants.

1 Determination of binding phosphorus

First measure the mass of total phosphorus, then measure the mass of inorganic phosphorus, total phosphorus minus inorganic phosphorus is equal to the mass of combined phosphorus.

1.1 Experiment

1.1.1 Principles

The organic part of the sample is decomposed by sulfuric acid, nitric acid and perchloric acid, and phosphorus is converted into orthophosphate, which forms yellow complex with vanadate and molybdate in acidic solution. The quality of phosphorus is determined by the absorption value of yellow complex.

1.1.2 Reagents and instruments

Ammonium molybdate aqueous solution: Dissolve 40g ammonium molybdate tetrahydrate in 500mL volumetric bottle, add 400mL hot distilled water to dissolve, and cool to room temperature. Diluted with distilled water to the scale, this solution is solution A.

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

Standard phosphate solution (KH2PO4): accurately weigh 1.1g±0.1mg potassium dihydrogen phosphate (must be dried overnight in the oven at 105℃ to the pharmacopoeia standard) and dissolve in distilled water, diluted to 1L volume bottle.

Instrument: Model 721 spectrophotometer.

1. 1.3 Operations

Operation: Accurately weigh the sample of 0.10-0.15g into 250mL conical bottle, add 6mL concentrated H2SO4, and slowly heat on the electric furnace until dissolved. After cooling, add 4mLn(HNO3)∶n(HClO4)= 3:1 aqueous solution, boil to colorless solution, cool, add 30mL distilled water, add zeolite, continue boiling for 4min, after cooling, transfer to 500mL volumetric bottle, thin to scale. Transfer 50mL into A 100mL volumetric bottle, add 2 to 3 drops of phenolphthalide indicator liquid with a mass fraction of 0.1%, adjust the solution with a concentration of 5mol/LNaOH to pink, add 5mL of mixed reagent (A solution and B solution mixed in equal volume), dilute it with distilled water to the scale, place it for 20min, and measure the absorbance at 460nm wavelength Check the mass of phosphorus on the curve.

Drawing of the standard curve: 0.0, 1.0, 2.0, 3.0, 4.0, 5.0mL of standard phosphate solution and 5mL of mixed reagent were added to the 100mL volumetric bottle, diluted to 100mL with distilled water, and absorbance was measured with a 1cm cupola at 460nm of the 721 spectrophotometer, while a blank experiment was performed. Draw a standard curve.

Calculation: Total phosphorus :ω(P)=V×0.2279×10-2/m×100%

ω(bound phosphorus)= ω(total phosphorus)-ω(inorganic phosphorus)

Where, V refers to the volume (mL) of phosphorus obtained on the standard curve,02279×10-2 refers to the mass (g) of phosphorus corresponding to the standard solution per milliliter, and m refers to the mass (g) of the sample.

1.2 Results and discussion

1.2.1 Selection of maximum wavelength

When the standard phosphorus sample of 3.0mL is measured on the instrument, the wavelength and sensitivity are selected with a 1cm colorimetric dish. Wavelength λ:460nm; Sensitivity :2 stops.

1. 2.2 Choice of acidity

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

1.2.3 Comparison of color development time

Take 5mL standard phosphate solution to do the color development time experiment.

Color development time has little effect on absorbance. After 48h, the absorbance does not change, and the color development time can be selected from 15 to 20min.

2 Determination of inorganic phosphorus

2.1 Experiment

2.1.1 Principles

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

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

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

2.1.2 Reagents and instruments

Same as the determination of total phosphorus.

2.1.3 Procedure

Operation: Accurately weigh the sample of 0.1-0.2g, place it in the centrifuge tube, add hot anhydrous ethanol to 2/3 of the centrifuge tube, stir well, separate with centrifuge, pour out the clear liquid, repeat. Add distilled water to the precipitation to dissolve the precipitation, transfer to A 250mL conical bottle, add 50mL distilled water and 3mL nitric acid, boil for 10min, cool, transfer to a 250mL volumetric bottle, add 2~3 drops of phenolphthalide solution, drop the solution with a concentration of 5mol/LNaOH to pink, then add 5mL of mixed reagent (A and B are mixed in the same volume), and steam The distilled water is diluted to the scale, and the absorbance is measured at 460nm with a spectrophotometer.

Standard curve drawing: same total phosphorus.

Calculation: Inorganic phosphorus =V×0.2279×10-2×2.5/m×100% formula :V - the volume of phosphorus obtained from the phosphate standard curve (mL),0.2279×10-2 - the mass of phosphorus per millilitre of the standard solution (g),m - the mass of the sample (g).

2.2 Results and discussion

2.2.1 Selection of separation conditions

Whether the separation is complete or not has a great influence on the results of inorganic phosphorus analysis. Organic phosphorus is known to dissolve in alcohol, while inorganic phosphorus is insoluble, and ethanol is used to separate inorganic phosphorus from organic phosphorus. In addition, the amount of weighing sample also has an impact on the separation effect, and it is appropriate to choose weighing sample control in 0.1-0.2g. Precipitation washing should pay attention to whether the washing is thorough. When water is added to dissolve, if the centrifugal effect is not good, more centrifugal washing should be done.

2.2.2 Decomposition of polyphosphate

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

3 Conclusion

The quality of inorganic phosphorus and bound phosphorus in phosphate ester can be determined by this method. The results are accurate and easy to operate, and have been used in the analysis of actual samples.