Zborník príspevkov z vedeckej konferencie - Department of ...

applied to attain a stabilization of the most phosphorus matrix without any loss of the analyte. In the presence of 10 g of Pd
plus 10 g of La up to 25g of phosphorus (in the form of NaNH4HPO 4) can be tolerated without changes of sensitivity. It
can be seen from Fig. 3, that using Pd + La(NO 3) 3 modifier, an increase of absorbance at the 213.6 nm line (phosphorus
atomic absorption) for temperatures above 600 °C is less pronounced, in comparison with conditions when only La(NO 3)3
was used as a modifier.
The optimal amounts of analyte and matrix modifiers were determined by interpretation of dependency of normalized
integrated absorbance of analyte versus modifier weight. Peak shapes were also taken into consideration for optimization of
the modifier mass. From figures it is evident, that lanthanum effectively stabilizes phosphorus species in solid samples from
10 g amount and palladium stabilizes Pb completely fom 10 g per atomization.
For practical purposes the addition of ammonium nitrate (200 g per atomization) to mixed modifier increased the
robustness against possible chloride interference and also improves the mineralization of the solid matrix during pyrolysis
stage. The amount of additional matrix modifier, ammonium nitrate, was not optimized. It can be noticed that the palladiumammonium
nitrate-lanthanum mixed modifier provided about 5% higher sensitivity compared with palladium-lanthanum
modifier.
Fig. 2a.: Optimization of the amount of matrix modifier
(constant amount 10 g of palladium modifier and 200
g of NH4NO3 were added, temperature program
according to Table 1, each point of the graph represents
the median of 3 independent measurements)
3.2. Analytical results of the method developed
Fig. 2b.: Optimization of the amount of analyte modifier
(Pd) (constant amount 10 g of La and 200 g of
NH 4NO3 were added, temperature program according to
Table 1, each point of the graph represents the median of
3 independent measurements)
Although calibration in SS-ETAAS has been considered a problematic part, several studies have shown that
calibrations with aqueous standards were satisfactory. Despite the fact, that application of the standard addition technique in
SS-ETAAS is more time-consuming than by the conventional ETAAS, it was applied in this study in order to compare the
results obtained with this technique and the technique of external calibration, using aqueous calibration solutions. To
investigate the feasibility of aqueous calibration curves for quantification, the atomization profiles of solid samples were
compared with the peak profiles of the aqueous standards. As it can be seen in Fig. 3a in the presence of food matrix (BCR
189 wholemeal flour), for both, Pd+ NH 4NO3 and Pd+ NH4NO3+La addition, Pb atomic absorption signal appears before,
i.e. at the lower temperature when compared with matrix-free conditions. This fact can be attributed to the less efficient
analyte stabilization due to the presence of high amount of the interfering matrix. By using Pd+ NH4NO3+La ternary modifier
this effect is more pronounced. Also from Fig. 3a is evident, that some overcorrection is appeared in Pb atomic signal after
half-time of atomization. This side effect is related to incomplete phosphorus bonding due to lower efficiency of the
La(NO 3) 3 modifier in solid samples, compared to aqueous solutions. To avoid erratic result caused by mentioned
phenomenon the integration time was reduced to 3s if solid samples were atomized. On the Fig. 3b it is clearly showed, that
described mixed modifier has serious limitation, when extremely high amounts (10 mg or more) of solid samples were
analyzed.
The detection limit was calculated following the IUPAC recommendations as the concentration of lead which
corresponds to 3 times the standard deviation of blank. The detection limit obtained was 0.15 pg of Pb using described
Zborník príspevkov
z 18. medzinárodnej vedeckej konferencie
"Analytické metódy a zdravie loveka", ISBN 978-80-969435-7-9
- 73 -
hotel Falkensteiner, Bratislava
11. - 14. 10. 2010