Колориметрическое определение фосфатов

Измерение уровня фосфатов в воде молибденово-синим методом

Colorimetry Advanced (University) 90 мин ~$15,00

Цель

Определить концентрацию фосфатов в пробе воды молибдатно-аммониевым колориметрическим методом.

Предпосылки

The molybdenum blue method is the standard technique for phosphate determination in environmental water analysis. Phosphate ions react with ammonium molybdate in acidic solution to form a phosphomolybdate complex, which is then reduced by ascorbic acid to form an intensely blue colored complex (molybdenum blue). The intensity of the blue color is proportional to phosphate concentration. This method can detect phosphate at concentrations as low as 0.01 mg/L.

Предупреждения по безопасности

  • Ammonium molybdate solution contains sulfuric acid — corrosive
  • Antimony compounds are toxic
  • Use pipette fillers — never mouth-pipette
  • Dispose of molybdate waste in heavy metal waste container

Требуемые СИЗ

goggles gloves lab_coat

Материалы

  • Potassium dihydrogen phosphate (KH₂PO₄) (1 g)
    For stock standard
  • Ammonium molybdate solution (100 mL)
    2.5% in 5M H₂SO₄
  • Ascorbic acid solution (50 mL)
    1% freshly prepared
  • Antimony potassium tartrate (10 mL)
    Catalyst solution
  • Environmental water sample (100 mL)
    Pond, river, or tap water
  • Distilled water (500 mL)

Оборудование

Spectrophotometer Cuvettes (1 cm path length) Volumetric flasks (50 mL, 8 total) Pipettes (1 mL, 5 mL, 10 mL) Water bath (37°C)

Процедура

1

Prepare a 100 ppm phosphate stock solution by dissolving 0.1433 g KH₂PO₄ in distilled water and making up to 1 L. Then prepare working standards: 0, 0.1, 0.2, 0.5, 1.0, 2.0 ppm.

15 мин
2

Prepare the combined reagent: mix 50 mL ammonium molybdate solution, 5 mL antimony potassium tartrate solution, and 30 mL ascorbic acid solution. Use within 4 hours.

10 мин Handle acid carefully
3

To each 50 mL standard flask and the water sample, add 8 mL of combined reagent. Mix well.

10 мин
4

Allow color development for 10 minutes at room temperature (or 5 minutes in 37°C water bath).

10 мин
5

Measure absorbance at 880 nm (or 710 nm if 880 nm is not available). Zero with the blank.

15 мин
6

Plot the calibration curve. Determine the phosphate concentration of the water sample.

15 мин
7

Evaluate the result against environmental standards. Phosphate above 0.02 mg/L may indicate eutrophication risk.

15 мин

Ожидаемые результаты

The calibration curve should be linear in the 0–2 ppm range. The blue color deepens with increasing phosphate. Environmental samples typically show 0.01–0.5 ppm in clean water, higher in agricultural runoff areas.

Уборка

Collect all molybdate-containing solutions in labeled waste. Rinse all volumetric glassware. Clean cuvettes immediately.

Детали

Категория
Colorimetry
Сложность
Advanced (University)
Продолжительность
90 мин
Прим. стоимость
$15,00
Шаги
7
Материалы
6

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Frequently Asked Questions

What is the objective of Колориметрическое определение фосфатов?
Определить концентрацию фосфатов в пробе воды молибдатно-аммониевым колориметрическим методом.
How difficult is Колориметрическое определение фосфатов?
This experiment is rated as Advanced (University). It takes approximately 90 minutes to complete.
What safety precautions are needed for Колориметрическое определение фосфатов?
Key safety precautions include: Ammonium molybdate solution contains sulfuric acid — corrosive; Antimony compounds are toxic; Use pipette fillers — never mouth-pipette.
What materials are needed for Колориметрическое определение фосфатов?
The main materials required are: Potassium dihydrogen phosphate (KH₂PO₄), Ammonium molybdate solution, Ascorbic acid solution, Antimony potassium tartrate, Environmental water sample.
What results should I expect from Колориметрическое определение фосфатов?
The calibration curve should be linear in the 0–2 ppm range. The blue color deepens with increasing phosphate. Environmental samples typically show 0.01–0.5 ppm in clean water, higher in agricultural runoff areas.