Cadmium- Determination by AAS
COEI-2-CADMIU Determination of cadmium by atomic absorption spectrometry
- Principle
The cadmium is determined in solid oenological products after mineralisation by wet process or directly for liquid oenological products or put in a solution.
The determinations are performed by atomic absorption without a flame (electro-thermal atomisation in a graphite oven).
- Apparatus
2.1. Instrumental parameters (given as an example)
Spectrophotometer equipped with an atomiser with a graphite tube.
- wave length: 228.8 nm
- hollow-cathode lamp (cadmium)
- width of slit: 1 nm
- intensity of the lamp: 3 mA
- correction of continuum by the Zeeman effect
- graphite oven with a tantalised platform
- (tantalisation procedure of the platform described above)
- adjusting the oven for an analysis:
|
step |
temperature (°C) |
time (s) |
gas flow rate ( / mn |
type of gas |
reading of signal |
|
1 |
100 |
35 |
3.0 |
argon |
no |
|
2 |
500 |
10 |
3.0 |
argon |
no |
|
3 |
500 |
45 |
1.5 |
argon |
no |
|
4 |
500 |
1 |
0.0 |
argon |
no |
|
5 |
2250 |
1 |
0.0 |
argon |
yes |
|
6 |
2250 |
1 |
0.0 |
argon |
yes |
|
7 |
2500 |
2 |
1.5 |
argon |
no |
|
8 |
1250 |
10 |
3.0 |
argon |
no |
|
9 |
75 |
10 |
3.0 |
argon |
no |
2.2. Adjustments of the automatic sampler (given as an example)
|
volumes injected in µl |
|||
|
solution of Cd at 8 μg/l |
blank |
matrix modifier |
|
|
blank |
0 |
10 |
2 |
|
calibration N° 1 at 8 μg / l |
1 |
9 |
2 |
|
calibration N° 2 at 16 μg / l |
2 |
8 |
2 |
|
calibration N° 3 at 24 μg / l |
3 |
7 |
2 |
|
calibration N° 4 at 32 μg / l |
4 |
6 |
2 |
|
Sample to be dosed |
5 |
5 |
2 |
- Reagents
- Demineralised water
- Pure nitric acid for analysis at 65%
- Anhydrous palladous chloride (59% in Pd)
- Magnesium nitrate with 6 water molecules (ultra pure)
- Ammonium dihydrogenophosphate
Matrix modifier: palladous chloride and magnesium nitrate mixture (dissolve 0.25 g of PdCl2 and 0.1 g of Mg(NO3)2.6H2O in 50 ml of demineralised water) or ammonium dihydrogenophosphate at 6% (dissolve 3 g of NH4H2PO4 in 50 ml of demineralised water).
Cadmium reference solution at 1 g/l, commercial or prepared as follows: dissolve 2.7444 g Cd(NO3)2.4H2O in a solution of HNO3 0.5 M, adjust to 1 l with HNO3 0.5 M.
Cadmium solution at 10 mg/l: place 1 ml of the reference solution in a 100 ml graduated flask, add 5 ml of pure nitric acid and complete to volume with demineralised water.
Cadmium solution at 0.8 g/l: place 4 ml of the diluted solution in a 50 ml graduated flask, add 2.5 ml of pure nitric acid and complete to volume with demineralised water.
Calibration range at 0, 8, 16, 24 and 32 μg/l of cadmium.
- Preparation of samples
No preparation is necessary for liquid oenological products or in solution form; solid products are mineralised by wet process.
The blank solution is made up of a pure nitric acid solution for analysis at 1%.
- Procedure
Each calibration solution is passed right after the blank solution. Perform 2 successive absorbance readings and establish the calibration curve.
Calculate the cadmium content of the samples while taking into account the test sample of different dilutions.