Lead- Determination by AAS
COEI-2-PLOMB Determination of lead by atomic absorption spectrometry
- Principle
After mineralisation of the sample in an acid medium, the lead is determined by spectrometry without flame (electro-thermal atomisation).
- Apparatus
2.1. Instrumental parameters: (given as an example)
Atomic absorption spectrophotometer equipped with an atomiser with a graphite tube
- wave length: 283.3 nm
- hollow-cathode lamp (lead)
- width of slit: 0.5 nm
- intensity of the lamp: 5 mA
- correction of continuum: by Zeeman effect
- introduction in hot conditions of the samples in the graphite oven by an automatic distributor (rinsing water contains 2 drops of Triton per litre)
- measurement of signal: peak height
- time of measurement: 1 second
- number of measurements per sample: 2
- pyrolytic graphite tube
- pyrolytic graphite oven containing a platform of L’Vov
- tantalised (tantalisation of a platform: see above).
Parameters for oven
|
temperature (°C) |
time (s) |
gas flow rate (l / min) |
type of gas |
Reading of signal |
|
150 |
20.0 |
3.0 |
argon |
no |
|
150 |
35.0 |
3.0 |
argon |
no |
|
800 |
15.0 |
3.0 |
argon |
no |
|
800 |
30.0 |
3.0 |
argon |
no |
|
800 |
2.0 |
0.0 |
argon |
no |
|
2250 |
0.8 |
0.0 |
argon |
yes |
|
2250 |
1.0 |
0.0 |
argon |
yes |
|
2500 |
1.0 |
1.5 |
argon |
no |
|
1200 |
9.0 |
3.0 |
argon |
no |
|
75 |
10.0 |
3.0 |
argon |
no |
2.2. Adjustments of the automatic sampler
(given as an example)
|
volumes injected in μl |
|||
|
lead solution at 50 μg/l |
blank |
matrix modifier |
|
|
blank |
0 |
10 |
2 |
|
calibration N° 1 |
1 |
9 |
2 |
|
calibration N° 2 |
2 |
8 |
2 |
|
calibration N° 3 |
3 |
7 |
2 |
|
calibration N° 4 |
4 |
6 |
2 |
|
calibration N° 5 |
6 |
4 |
2 |
|
Sample to be measured |
10 |
0 |
2 |
- Reagents
3.1. Pure demineralised water for analysis
3.2. Pure nitric acid for analysis at 65%
3.3. Ammonium dihydrogenophosphate
3.4. Matrix modify: ammonium dihydrogenophosphate at 6%.
Introduce 3 g of ammonium dihydrogenophosphate in a 50 ml graduated flask, dissolve and complete to volume with demineralised water.
Lead reference solution at 1 g/l commercial or prepared as follows: dissolve 1.5985 g of pure Pb(NO3)2 for analysis in a solution of HNO3 0.5 M, adjust at 1 l avec HNO3 0.5 M.
Lead solution at 10 mg / l: place 1 ml of the reference lead solution at 1 g/l in a 100 ml graduated flask; add 1 ml of nitric acid at 65% complete to volume with pure demineralised water for analysis.
Lead solution at 0.1 mg/l: place 1 ml of the lead solution at 10 mg/l in a 100 ml graduated flask, add 1 ml of nitric acid at 65%; complete to volume with pure demineralised water for analysis.
Set of calibration solutions: 0, 50, 100, 150, 200, 300 µg/l of lead.
The automatic distributor cycle allows to directly inject these quantities of lead on the platform from the lead solution at 0.050 mg/l.
- Preparation of samples
- The liquid or solution samples must have concentrations between 0 and 300 μg/l of lead.
- The solid samples will be mineralised by wet process (attack by nitric acid).
- The blank is made up of pure water for analysis containing 1% of nitric acid at 65%.
- Procedure
The calibration curve represents the variations of absorbencies depending on the concentrations enabling to calculate the lead content of the samples.