Environmental Engineering LaboratoryBy: Ngoc Thuan Le

Ammonia (NH4+-N phenolate method)

Note: for high ammonia concentration a distillation and titration technique is preferred.

Storage of samples: to destroy residual chlorine to prevent its reaction with ammonia. If prompt analysis is impossible, preserve samples with 0.8ml conc H2SO4/l sample and store at 4oC, pH 1.5-2.0.

Apparatus

Water bath, Volumetric tubes, Spectrophotometer.

Procedure

1. Use pipet place 30ml of sample to volumetric tubes.2. Add 10ml solution of sodium phenolate (나트륨 페놀 라이트)3. 1ml of Na2Fe(CN)5(NO).2H2O 0.15% (w/v) (sodium nitroprusside- 니트로프로싯트

나트륨 액)4. Add 5ml solution of NaClO 4.7% (v/v) (sodium hypochlorite- 차아얨 소산)5. Wait for 30 minutes, at room temp. Solution color will be blue6. Bring volume to 50ml.7. Measure color photometrically at 630nm and compare with calibration curve, using

distilled water blank.8. Prepare blank sample with distilled water.9. Standard curve: prepare solution of ammonia with concentration of 0.005 mgN/ml (5

mgN/ L), use 0.5 – 10 ml, adding DW until 30ml for measurement standard curve.

Calculation

Reagents- Sodium phenolate: phenol 25gr (~23.4ml) + 55ml NaOH 20% (w/v) -cooling,

add 6ml acetone. Bring the volume to 200ml with dW. Storge in the dark, prepare weekly.

- Na2Fe(CN)5(NO).2H2O 0.15% (w/v) (sodium nitroprusside): dissolve 0.15g chemical powder with 100ml dW. Storage in the dark.

- NaClO 4.7% (v/v) sodium hypochlorite, we can use the concentration range of 5~12%: 4.7ml NaClO + dW, bring volume to 100ml.

- NaOH 20% (w/v): 20gr of NaOH, dissolve in 100ml of solution with dW.- Standard sol. 19.1 mg NH4Cl/1000ml (prepare 10X sol.: 191mg NH4Cl in 1 L,

dilute 10 times before using for standard curve measurement)