Determination of Manganese Content in Water by Formaldehyde Oxime Spectrophotometry

  Formaldehyde oxime is a compound formed by the action of carbonyl-containing aldehydes, ketones and hydroxylamine. This compound can form a brown-red compound with manganese in an alkaline solution. The absorbance of this brown-red compound can be measured. The content of manganese is obtained by the formula.
  Through this property, it can be used to detect the total manganese content in drinking water or other water sources. The minimum detection mass is 1.0ug. If a 50mL water sample is taken for determination, the minimum detection mass concentration is 0.02mg/L.

Instruments used for testing

1. Conical flask 100mL
2. Colorimetric tube with stopper 50mL
3. Spectrophotometer

Reagents used for testing

1. Nitric acid
2. Potassium Persulfate
3. Sodium sulfite
4. Ferrous ammonium sulfate solution
Weigh 700 mg of ferrous ammonium sulfate, add 10 mL of sulfuric acid solution (1+9), and dilute to 1000 mL with laboratory-grade pure water.
5. Sodium hydroxide solution (160g/L)
Weigh 160 g of sodium hydroxide, dissolve it in laboratory first-grade pure water, and dilute to 1000 mL.
6. Disodium EDTA solution (372g/L)
Weigh 37.2 g of disodium EDTA, add about 50 mL of sodium hydroxide solution, stir until completely dissolved, and dilute to 100 mL with laboratory first-grade pure water.
7. Formaldehyde oxime solution
Weigh 10g of hydroxylamine hydrochloride and dissolve it in about 50mL of laboratory first-grade pure water, add 5mL of formaldehyde solution, dilute to 100mL with laboratory first-grade pure water, and store the reagent in a cool place for at least 1 month.
8. Ammonia solution (0.88g/mL)
Measure 70 mL of ammonia water, and then dilute to 200 mL with laboratory-grade pure water.
9. Hydroxylamine hydrochloride solution (417g/L)
Weigh 41.7g of hydroxylamine hydrochloride solution in laboratory first-grade pure water and dilute to 100ml.
10. Ammonia Hydroxylamine Hydrochloride Solution
The above ammonia solution and hydroxylamine hydrochloride solution were mixed in equal volumes.
11. Manganese standard stock solution (1mg/mL)
Weigh 1.2912g of manganese oxide or 1.000g of metal manganese, add nitric acid (1+1) to dissolve, and use laboratory first-grade pure water to dilute to 1000mL.
12. Manganese standard solution (10ug/L)
Pipette 5.00mL manganese standard stock solution and dilute to 500mL with laboratory first-grade pure water.

Detailed inspection steps

1. Water sample pretreatment
  If the collected water sample to be tested contains suspended manganese and organic manganese, you can test it after pretreatment, take a certain amount of water sample in a conical flask, add 0.5 mL of nitric acid and 0.25 g of potassium persulfate per 50 mL of water sample , put a few glass beads, boiled on the electric stove for 30min, removed and cooled slightly, filtered with fast qualitative filter paper, and washed the filter paper with dilute nitric acid solution several times. About 0.5 g of sodium sulfite was added to the filtrate, and the volume was adjusted to a certain volume with pure water as a test solution.

2. Detect water samples
   Take 50mL of clean water sample or test solution in a 50mL colorimetric tube.
   In addition, take 8 50mL colorimetric tubes, add 0mL, 0.10mL, 0.25mL, 0.50mL, 1.00mL, 2.00mL, 3.00mL and 4.00mL manganese standard solution respectively, and add laboratory first-grade pure water to the mark.
Add 1.0 mL of ferrous ammonium sulfate solution and 0.5 mL of disodium EDTA solution to the water sample and standard series tubes. After mixing evenly, add 0.5 mL of formaldehyde oxime solution, and immediately add 1.5 mL of sodium hydroxide solution. After mixing evenly, open the stopper and let stand for 10 min.
   Add 3 mL of ammoniacal hydroxylamine hydrochloride solution and leave it for at least 1 hour. If the room temperature is lower than 15 °C, it can be placed in a warm water bath, and then at a wavelength of 450 nm, use a 5 cm cuvette with laboratory first-grade pure water as a reference to measure its value. absorbance.
   Draw the standard curve, find out the quality of manganese in the water sample tube, and calculate the total manganese content in the tested water sample by formula.