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CADMIUM - DOSAGE PAR SAA

COEI-2-CADMIU Determination of cadmium by atomic absorption spectrometry

  1. 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).

  1. 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

  1. 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.

  1. 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%.

 

  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.