Zborník príspevkov z vedeckej konferencie - Department of ...

different atomization signal profiles, which indicates that the solid matrix has significant influence on the appearance time
and atomization kinetics. Even using atomization temperature of 2500°C the atomic signal of Sn from the soil samples is
showing high asymmetry and long tailing, which is probable due to the several different chemical forms of the analyte
presented in the sample. The matrix effect and incomplete analyte recovery was confirmed comparing the slopes of
calibration curve and standard addition method. The mentioned comparison gives difference 22±3% for solid sample S-SP.
Because of several adverse effects a modifier is required to suppress these phenomena.
Some experiments were carried out in order to check the possible elimination of the adverse effects that could be
derived from the use of a modier. The furnace heating parameters were fixed at 1000°C (pyrolysis temperature) for 30 s
with 50°C s -1 heating ramp and 2400°C (atomization temperature) for 6 s with 3000°C s -1 heating ramp during preliminary
studies. Palladium (10; 25; 50 g), Mg(NO 3) 2 (1; 5; 10 g), ammonium dihydrogen phosphate (200; 500g) were evaluated
for this purpose using aqueous solutions of tin (20.0 ng) and a soil sample S-SP. It was found that ammonium dihydrogen
phosphate hardly produces any variation in the tin signal, palladium produces an increased sensitivity and Mg(NO 3)2
considerably improved the signal prole of Sn in solid sample. The enhanced atomization profile may be caused by matrix
depletion by MgO. When 50 g of palladium were added to solid or liquid samples a significant tailing of Sn signal was
obtained from both medium due to over-stabilization of the Sn. Taking into consideration these results, the combination of
palladium (25g) and magnesium nitrate (10 g) was used in further experiments.
As can be seen from Fig. 2., the use of Pd and magnesium nitrate mixture made the signal obtained from tin solutions
similar regardless of whether they contained potentially interfering matrix elements in solution (mixture of 5 g Ca, 10 g
Al, 2.5 g Fe, 25 g Si, 0.1 g P) or not. However, when these conditions were applied to solid samples the atomic signal of
Sn shows moderate tailing compared to the Sn signal from solutions. It seems obvious that the modier is less effective with
a solid sample than with solutions, probably due to the fact that in a solution the palladium-tin interaction begins already
during the drying step whereas in solid samples it cannot take place until the matrix is destructed in the pyrolysis step. The
interaction is thus limited because not all the tin is liberated from the matrix. In order to facilitate the action of the modier,
the atomization programe was modied by splitting the pyrolysis in two steps. The first pyrolysis step was performed with
addition of 10 g Mg(NO3) 2 at 500°C, the minimum temperature which permits fusing the matrix with MgO. The magnesium
oxide (from thermal decomposition of Mg(NO3)2) may help to destroy the siliceous matrix and release the Sn trapped in the
matrix. The temperature selected is below the boiling point of SnCl 2, thus avoiding tin losses. During the second pyrolysis
step palladium modifier is applied to obtain a well-dened signal. As we can see in Fig. 2., using a double pyrolysis step the
absorption signal of tin appears sooner and is better dened, the most important is, there is an increase in the peak height of
the absorbance signal, so that the signal obtained from the solid sample is similar to that obtained from solution under the
same conditions. The background absorption becomes insignificant even when the atomization temperature is high as
2400°C.
Absorbance
0,4
0,3
0,2
0,1
0,0
0 1 2 3 4 5
Time, s
Fig. 2.: Atomic absorption signal profiles of Sn in aqueous standard and solid samples in presence of mixed modifier
consisting of 25 g Pd and 10 g Mg(NO 3) 2 (1a-10.0 ng Sn in aqueous standard, 1b-9.8 ng Sn in 0.487 mg soil S-SP, 1c-10.0
ng Sn in aqueous standard in presence of mixture of potentially interfering elements: 2.5 g Ca, 10 g Al, 2.5 g Fe, 25 g
Si, 0.1 g P, 2a-10.0 ng Sn in aqueous standard, 2b-10.2 ng Sn in 0.507 mg soil S-SP; 1: one step pyrolysis, 2: two step
pyrolysis.)
Zborník príspevkov
z 18. medzinárodnej vedeckej konferencie
"Analytické metódy a zdravie loveka", ISBN 978-80-969435-7-9
- 45 -
1c
1a
2b
2a
1b
hotel Falkensteiner, Bratislava
11. - 14. 10. 2010