2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

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