1. Principle:
The sample is digested in H2SO4, using CuSO4.5H20 as catalyst with K2SO4, to release nitrogen from protein and retain nitrogen as ammonium salt. Concentrated NaOH is added to release NH3, which is distilled, collected in H3BO3 solution, and titrated in HCl.
2. References:
TCVN – 1: 2009, ISO 8968-1: 2001
3. Apparatus:
- Analytical balance, sensibility 0.001g
- Kjeldahl digestion appatus.
- Distillation system.
- Erlen 250ml
- Burret 25ml
4. Apparatus:
- Acid sulfuric H2SO4 (95 – 98%)
- Methyl red/bromocresol green indicator solution.
- Acid boric H3BO3 4%
- Acid HCl 0.1N
- K2SO4 and CuSO4.5H2O
5. Procedure:
Sample Preparation: Pour successively into digestion tube:
- The sample (m): Non Dairy Creamer: 0.8g and the blank: 0.85g saccharose
- K2SO4+CuSO4.5 H2O: 5g
- H2SO4 (95 – 98%): 15ml
Digestion:
- Turn on the fume extraction system of the degestion apparatus prior to beginning the degestion.
- Total time digestion about 1,5 hours.
- After digestion is cooled to room temperature, add 40 – 50ml H2O. Avoid formation of crystalline
- Let mixture cool to room temperature before distillation.
Distillation:
- Add 50ml H3BO3 solution to erlenmeyer 500ml (Additional Methyl red/bromocresol green indicator solution).
- Turn on distillation system. Wait 5 minutes. After the system is ready, the display shows the following message: “Vapodest 20s Standby”
- Digestion tube and erlenmeyer into distillation system (check correct fit of the tube). Close protection door.
- The display show the standby mode
Titration:
- Titrate receiving solution with standard 0.1N HCl solution. And read using volume HCl (V)
6. Calculation:
Note:
-
V0: ml titrant used for blank (ml)
-
V: ml titrant used for sample (ml)
-
N: solution concentration HCl (N)
-
m: weight of sample (g)
-
k= 6.38: conversion factor form total N to protein crude