Sample
mineralization
The
non-soluble fraction of atmospheric
samples (aerosol + residual fraction in
rainwater) is mineralized prior to
analysis. The organic matrix is destroyed
with an oxidizing attack (HNO3),
and mineral aluminosilicate matrixes are
destroyed with HF. The sample is
freeze-dried and weighed (weighing
machine Sartorius MC 1, accuracy 0.01 mg)
in 7 ml flasks, where the mineralization
will take place. Then, the procedure can
be decomposed in two main steps:
1)
900 µl HNO3 65% are added to
each flask. The flasks are closed and put
into larger bottles (60 ml) that act as
expansion cells, overcome acidic
evaporation and help to prevent
contamination. This apparatus is left 2 -
3 hours in an oven at 60 °C, and then 3
- 4 hours at 150 °C, until remains a
black dry residue.
2)
200 µl HNO3 65% and 200 µl HF
40% are added to the remainder. The
samples are put in an oven 2 - 3 hours at
60 °C, and then 3 - 4 hours at 150 °C,
until a white dry residue is obtained.
This residue is ultrasonically dissolved
in 0.5 ml HNO3 1N. The samples
are then made up with Milli-Q water to 5
ml.
All
reagents were provided by Merck
(Darmstadt, Germany), quality Suprapur
(HCl), Normapur (HNO3) and Pro
Analysis (HF).
ICP-AES
analysis
Al,
Na and Zn are analysed by inductively
coupled plasma atomic emission
spectroscopy (ICP-AES). ICP-AES
measurements are performed with a
Jobin-Yvon JY 38 S Ultrace analyser,
equipped with a Scott nebulizer.
Detection limits are 25, 50 and 5 mg
l-1 for Al, Na and Zn,
respectively. Blank values (filter +
reagents) are
always lower than the detection limits.
The
analytical procedure is checked regularly
using certified reference materials
provided by the National Research
Council, Ottawa, Canada; the discrepancy
is generally less than 10%
(Sandroni, 2000). All analyses are
carried out in Class 100 laminar airflow
benches located within a clean room.
More
details can be found in Journel (1998)
and Sandroni (2000).
Filter
holder Sartorius (SM 16510)
