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3. Results and discussion
3.1. Method development for liquid sampling ETAAS
A study of the best conditions for graphite furnace determination was carried out. Several mixed chemical modifiers: 5
g Pd + 3 g Mg(NO3) 2 [18], 5 g Pd + 1000 g citric acid + 100 g NH 4F [19], 1000 g citric acid + 100 g NH 4F, 1000
g ascorbic acid + 100 g NH4F and 100 g NH4NO3 + 100 g NH4F were tested in order to improve atomization signal
profile, sensitivity and overcome matrix effects. The operating conditions were optimized considering the maximum
pyrolysis temperature, atomization temperature, atomic peak shape and the best separation between the atomic and
background profiles for each modifier. For the study of optimal furnace parameters 1.0 ng of Sn in standard solution, aqua
regia extract and total dissolution of S-SP sample were used. The elimination of the matrix effect was checked by comparing
the slope of calibration curve and standard addition method (10 L of 50 and 100 g L -1 concentrations of Sn as standard
additions).
Table 2. The analytical performance of tested modifiers
Optimal temperature of (°C) Slope of (s ng -1 )
Modifier
Pyrolysis Atomization
Aqueous
cal. curve
Standard addition of
aqua regia extract (S SP)
Standard addition
of tot. diss. (S-SP)
5g Pd + 3g Mg(NO3) 2 2500 1400 0.105 0.086 (82% a ) 0.055 (52% a )
5g Pd + 1000g CA +
100g NH4F
2500 1400 0.127 0.075 (59% a ) 0.046 (36% a 1000g CA+
+ 100g NH4F
2200 1200
0.145
0.132
)
b 0.136 (96% a )
0.126 (87% a )
(95% a ) b
1000g AA+
+ 100g NH4F
2200 1200
0.148
0.136 b 0.144 (97% a )
0.129 (86% a )
(94% a ) b
100g NH4NO3 +
+ 100g NH4F 2300 1100 0.076 0.053 (70% a ) 0.049 (65% a )
a
slope difference calculated as (slopestandard addition/ slopecalibration curve).100%, b matrix matching calibration by co-injecting of
2.5 g Ca (as Ca(NO3) 2) with the calibration solutions, CA citric acid, AA ascorbic acid
Absorbance
0,3
0,2
0,1
0,0
2a
1b
1c
1d
0 1 2 3 4 5
Time, s
Fig. 1.: Signal profiles of Sn in aqueous standard and 5-times diluted dissolved soil samples in presence of mixed modifier
consisting of 1000 g CA and 100 g NH 4F (pyrolysis temperature 1200°C, atomization temperature 2200°C, 1a-1.0 ng Sn
in aqueous standard, 1b-20 L of dissolved soil S-MS, 1c-20 L of dissolved soil S-MS, 1d-20 L of aqua regia extract of
soil S-MS, 2a-1.0 ng Sn in aqueous standard in presence of 2.5 g Ca, 2b-20 L of dissolved soil S-SP)
The pyrolysis temperatures varied between 700-1600°C. Pyrolysis temperatures lower than 700°C could not be used,
since matrix components were not eliminated efficiently under these conditions, and background was considerable, leading in
some cases to over-correction and, as a consequence, erroneous absorption values for the analytes. The ramp time for the
Zborník príspevkov
z 18. medzinárodnej vedeckej konferencie
"Analytické metódy a zdravie loveka", ISBN 978-80-969435-7-9
- 43 -
1a
2b
hotel Falkensteiner, Bratislava
11. - 14. 10. 2010