2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures
2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures
2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology<br />
Table II<br />
Sequential extraction procedure<br />
Step Metal phase Reagent<br />
1 Exchangeable 1 M naOAc (pH = 8.2)<br />
2 Carbonate 1 M naOAc (pH = 5)<br />
3 Mn-Fe oxides 0.04 M nH 2 OH . HCl<br />
in 25 % HOAc<br />
4 Organic 0.02 M HnO 3 , 30% H 2 O 2 (pH = 2),<br />
3.2 M nH 4 OAc in 20% HnO 3<br />
5 Residual conc. HF, HClO 4 , HCl<br />
S o l - G e l T e c h n i q u e<br />
Sol-gel is an amorphous solid prepared via sol-gel processing,<br />
in which a colloidal suspension (sol) is first formed<br />
by mixing a silicon (e.g. tetraethoxysilane-TEOS) alkoxide<br />
precursor, water, a co-solvent and an acid or base catalyst.<br />
Alkoxyl groups are removed by acid- or base-catalysed hydrolysis<br />
reactions (Eq. (1)), and networks of O – Si – O linkages<br />
(gel) are formed in subsequent condensation reactions, which<br />
can produce either water or alcohol as shown in equations<br />
(2) and (3), involving hydroxyl groups 11 . Internal standard is<br />
integrated with the sample during gelation process.<br />
Hydrolysis:<br />
Si(OR) 4 + H 2 O → Si(OR) 3 OH + ROH (1)<br />
Condensation:<br />
X 3 SiOH + HOSiX’ 3 → X 3 Si – O – SiX’ 3 + H 2 O (2)<br />
X 3 SiOR + HOSiX’ 3 → X 3 Si – O – SiX’ 3 + ROH (3)<br />
An archive soil sample with the lowest content of Cr, ni,<br />
Cu, Zn and Pb spiked with solutions of elements of interest<br />
was used for the preparation of calibration samples. Twentytwo<br />
soil samples and three certified reference material of soils<br />
(GBW07405 – 07) were analyzed by developed LA-ICP-MS<br />
method and the obtained contents were compared with results<br />
of independent methods (XRF, ICP-OES).<br />
The real soil samples were treated by the following<br />
procedure: 1.2 g of soil was weighed into a 50 ml beaker<br />
and 3 ml of TEOS, 6 ml of ethanol, 1.5 ml of water, 20 µl<br />
of the Sc standard solution (100 mg ml –1 ) and two drops of<br />
0.01 mol dm –3 HnO 3 were added. The beakers were put into<br />
a thermostated water bath maintained at ~ 75 °C under ultrasonic<br />
stirring for ~ 1.5 h to reach the complete gelation. After<br />
20 min., 5 ml of water was added. The gelled materials were<br />
dried overnight in an oven at 110 °C. The sol-gel samples<br />
were manually ground and pressed into pellets with 12 mm<br />
in diameter and 1 mm thickness 10 .<br />
I n s t r u m e n t a t i o n<br />
A Jobin Yvon 170 Ultrace with laterally viewed ICP<br />
was used for solution analysis. The ICP system combines a<br />
s314<br />
monochromator and a polychromator. The monochromator<br />
was set on the Pb II 220.353 nm line and other four studied<br />
analytes were measured with the polychromator of a Paschen<br />
Runge montage using analytical lines Cr II 267.720 nm,<br />
ni II 231.608 nm, Cu II 324.759 nm and Zn I 213.860 nm.<br />
The XRF analysis was performed on an energy-dispersive<br />
XRF spectrometer (SPECTRO XEPOS) by polarized<br />
radiation, equipped with a Pd X-ray tube and a Si-detector.<br />
The real unknown samples were analyzed by the TUR-<br />
BOQUAnT method, which is able to analyze the elements<br />
na-U.<br />
The LA-ICP-MS was performed with a laser ablation<br />
system UP 213 (new Wave, USA) and an ICP-MS spectrometer<br />
Agilent 7500 CE (Agilent, Japan). A commercial Qswitched<br />
nd:YAG laser, operated at the wavelength of 213<br />
nm with the 5 th harmonic frequency, was used for ablation.<br />
The ablation device is equipped with programmable XYZstages<br />
that allowed sample movements during the ablation<br />
process. The samples were placed into the SuperCell (new<br />
Wave, USA) and were ablated by the laser beam, which was<br />
focused onto the sample surface through a quartz window.<br />
The ablated material was transported by flowing He to the<br />
ICP.<br />
Results<br />
The total contents of trace elements were determined<br />
using ICP-OES after total decomposition. XRF spectrometry<br />
was chosen for result comparison. Relative standard deviation<br />
of the total decomposition method and concentration range<br />
of tested soils can be found in Table I. Higher RSD value<br />
might be due to sample inhomogeneity and uncertainty of<br />
the measurement at low element concentration. Satisfactory<br />
agreement was found for ICP-OES solution analysis and<br />
XRF spectrometry. Correlation coefficient r values exceeded<br />
0.994. Comparison of Pn-ICP-OES and XRF determination<br />
of zinc as an easily leachable element is presented in Fig. 1.<br />
A five-stage sequential extraction procedure was used<br />
for the determination of the speciation of extractable heavy<br />
Fig. 1. Comparison of results obtained by xRF analysis and<br />
PN-ICP-OES of soil extracts for Zn I 213.860 nm