Water quality detector-Detailed detection steps of aniline compounds in water

  For aniline compounds in water, azo spectrophotometry can be used to detect the concentration range of 0.08mg/L-2.00mg/L. Its main principle is to combine aniline compounds with sodium nitrite under acidic conditions. Nitrogenation, and then coupled with N (1 naphthyl) ethylenediamine to generate purple dye. The absorbance was detected by a spectrophotometer, and the absorbance was proportional to the aniline content.

Instruments and reagents used for testing

1. Spectrophotometer

2. Electric furnace 300W

3. All-glass stills

4. Distillation unit

5. Zinc grains

6. Sodium hydroxide solution 1mol/L

Weigh 4g of sodium hydroxide and dissolve it in 100mL of laboratory pure water.

7. Sodium nitrite solution 50g/L

Weigh 0.5g of sodium nitrite and dissolve it in 10mL of laboratory pure water.

8. Hydroxylamine hydrochloride solution 200g/L

Weigh 10g of hydroxylamine hydrochloride and dissolve it in 50mL of laboratory pure water, put it in the refrigerator, it will be effective within 1 week.

9. N-(1-naphthyl)ethylenediamine solution

Weigh 0.5g N-(1-naphthyl)ethylenediamine hydrochloride, dissolve it in 100mL laboratory pure water, put it in the refrigerator, it is valid within two months.

10. Sulfuric acid solution 1mol/L

Take 28mL of sulfuric acid (p=1.84g/mL) and slowly add it to 1000mL of laboratory pure water, mix well, calibrate with sodium carbonate, and then adjust to 1mol/L.

11. Aniline Stock Solution

Add 5mL of 0.1mol/L hydrochloric acid solution to a 100mL volumetric flask, close the stopper tightly, weigh accurately, then add 1-2 drops of freshly distilled aniline, tighten the stopper, and weigh again, the difference between the two That is the weight of aniline, dilute to the mark with 0.1mol/L hydrochloric acid solution, shake well, and calculate the amount of aniline contained in each milliliter of the solution.

12. Aniline standard solution

According to the concentration of the stock solution of aniline, take out part of the solution and accurately dilute it with 0.1mo/L hydrochloric acid solution into a standard solution of 10mg/L aniline.

13. Phenolphthalein indicator

Weigh 0.5 g of phenolphthalein and dissolve it in 100 mL of absolute ethanol.

water sample pretreatment

1. Aniline is easily oxidized, so after collecting water samples, it should be stored in an environment of 5-10 °C, and the analysis should be carried out within 24 hours.

2. Take 50mL of the experimental sample, put it in a 250mL distillation flask, add 2-3 drops of phenolphthalein indicator, adjust it to red with 1mol/L sodium hydroxide solution, add 1mL, add 1-2 zinc particles, plug it for distillation bottle stopper.

3. Put 2.5mL sulfuric acid solution into the 50mL colorimetric tube for absorbing the distillate.

4. Put the distillation bottle on the electric furnace, connect the refrigerating tube to heat and distill, and stop heating when the distillate is about 50mL.

5. Dilute the distillate solution to 50mL with water, shake well, take out 25mL with a 50mL colorimetric tube, add 1 drop of sodium nitrite solution, shake well, leave for 15min, add 0.5mL hydroxylamine hydrochloride solution, shake well, tap gently At the bottom of the colorimetric tube, after the bubbles in the solution have completely escaped, add 1 mL of N-(1-naphthyl)ethylenediamine solution, shake well, and place it for 60min to be tested.

Check the specific steps

1. Determination of Aniline Compounds

  The wavelength of the spectrophotometer was set to 550 nm, and then the absorbance of the pretreated water sample was measured with a 10 mm cuvette.

2. Draw the working curve

  Take 8 250mL distillation flasks, draw 0mL, 0.40mL, 0.80mL, 1.60mL, 2.40mL, 3.20mL, 4.80mL, 8.00mL of aniline standard solution respectively, make up with water to 50mL, pretreat according to the detection steps, and then press related operations are measured. Taking the absorbance of each point measured minus the absorbance at zero concentration as the ordinate, the corresponding concentrations are 0mg/L, 0.08mg/L, 0.16mg/L, 0.32mg/L, 0.48mg/L, 0.64mg/L, 0.96mg /L and 1.60mg/L are the abscissas, and the working curve is drawn.

3. Blank test

  Use 50mL of first-grade pure water to replace the water sample for pretreatment operation, and then perform the determination according to the detection steps. The equivalent aniline concentration is measured from the working curve, and the reason should be checked if it exceeds the confidence zone.

  Finally, the absorbance of the water sample minus the absorbance of the blank test is the aniline concentration value of the measured water sample.