Environmental Engineering LaboratoryBy: Ngoc Thuan Le

Total Phosphorus (T-P) - ascorbic method

Principle: Ammonium molybdate and potassium antimonyl tartrate react in acid medium with

orthophosphate to form a heteropoly acid-phosphomolybdic acid that is reduced to intensely colored

molybdenum blue by ascorbic acid.

Apparatus

Volumetric tubes, incubator, Spectrophotometer.

Procedure

1. Place 50ml sample with 10ml solution of K2S2O8 4% w/v (potassium peroxodisulfate) in

100ml bottle.

2. Autoclave at 120oC, 30mins

3. Remove bottle from autoclave, take 25ml sample to the test tube.

4. Add 2ml solution of 5V (NH4)6Mo7O24 (ammonium molybdate) and 1V C6H8O7 7.2% (ascorbic

acid).

5. Keep at 20-40oC in incubator for 15 minutes (Don’t need to bring to final-50ml solution).

6. Measure color photometrically at 880nm and compare with calibration curve, using distilled

water blank.

7. Calibration curve: P-PO4 solution 0.005mg/ml (5mg/L)

Concentration range: 0, 1, 4, 5, 10ml

Calculation

a:

Reagents

- K2S2O8 4% w/v, dissolve 4gr K2S2O8 4% in 100ml solution.

- 6g of Ammonium molybdate ((NH4)6Mo7O24.4H2O, 1235.86) + 0.24 gr of antimonyl

Potassium tartrate 3-hydrate (C8H4K2O12Sb2.3H2O, 667.87) and 300ml of H2O. Then,

adding solution of 120ml H2SO4 (2+1) (mean 2V H2SO4+1V H2O) + 5gr ammonium

sulfamate (NH4OSO2NH2, 114.12), bring the solution to 500ml with water.

- Ascorbic 7.2% (w/v): dissolve 7.2 g ascorbic powder in 100ml dW (prepare when

using).

- Working solution: 5V ammonium molybdate solution: 1V ascorbic. This mixture is

stable for 4h.

- Standard solution, dissolve 0.439gr potassium phosphate monobasic (KH2PO4, 136.09)

in water to 1000ml (~ 0.1gr P-PO4 /L, 100mg/L, dilute 20 times before using to have

sol’s 5mg/L).

Environmental Engineering LaboratoryBy: Ngoc Thuan Le

- Solution for confirmation: dilute 25ml of standard solution to 500ml