2. ENVIRONMENTAL ChEMISTRy & TEChNOLOGy 2.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Environmental Chemistry & Technology
L08 COMPARISON OF ENERGy DISPERSIVE
x-RAy FLuORESCENCE SPECTROMETRy,
INDuCTIVELy COuPLED PLASMA OPTICAL
EMISSION SPECTROMETRy AND LASER
AbLATION wITh PLASMA SPECTROMETRy
IN ThE ELEMENTAL ANALySIS OF SOILS
IVOnA HUBOVá a , MARKéTA HOLá a , VLASTIMIL
KUBáň b , ILSE STEFFAn c and VIKTOR KAnICKý a
a Laboratory of Atomic Spectrochemistry, Department of Chemistry,
Faculty of Science, Masaryk University, Brno 611 37,
Czech Republic,
b Department of Chemistry and Biochemistry, Faculty of
Agronomy, Mendel University of Agriculture and Forestry,
Brno 613 00, Czech Republic,
c Department of Analytical Chemistry and Food Chemistry,
Faculty of Chemistry, University of Vienna, Vienna 1090,
Austria,
41396@mail.muni.cz
Introduction
Agricultural soils represent complex multiphase multicomponent
material which requires adequate methods of
chemical analysis. Content of elements represents important
parametre which relates to nutrition of plants on one side and
a contamination with toxic elements on the other side. For
intake of elements by plants only selected elemental forms
(species) are bioavailable. Speciation or fractionation based
on selective leaching of particular species followed by atomic
absorption spectrometry or inductively coupled plasma
optical/mass spectrometry (ICP-OES, ICP-MS) analyses of
resulting solutions are employed for this purpose. nevertheless,
total elemental contents, which comprise also elemental
forms that are insoluble in leaching media or by the action of
plants, might be interesting for overall characterisation of a
particular soil. In this case, total sample decomposition procedures
based on the action of a mixture of mineral acids or
a sample fusion with a suitable melt are applied to dissolve
resistant minerals and desintegrate possibly present silicate
lattice.
However, some methods for direct analysis of solids
are more advantageous because of elimination of possible
analytes losses and minimization of risk of contamination.
For this purpose, X-ray fluorescence (XRF) spectrometry 1 is
frequently and routinely used. Laser-assised plasma spectrometry
techniques, such as laser induced breakdown spectroscopy
2 , and ICP-OES or ICP-MS in connection with laser
ablation (LA) seem to be promising tool for soil analysis. 3–7
The aim of this work consists in establishing new
methods of soil elemental analysis using LA-ICP-OES/MS.
Artificially intentionally contaminated archive soil samples
were employed. Toxic metals Cr, ni, Cu, Zn and Pb were
considered in the method developement. For the method
validation, these soil samples were subjected to ICP-OES
analysis of solutions obtained by total decomposition using
mineral acids. Seleted soil standard reference materials were
s313
also analyzed. Independent results acquired by XRF analysis
of soil sample pellets were used for confirmation of accuracy
of solution analysis by ICP-OES.
Besides the total elemental content determination,
selected soils were characterized by means of the five-step
extraction procedure to asses elemental fractions bound to
particular soil phases. This information might be important
for explanation of possible matrix effects associated with
processes of LA.
A selection and preparation of a suitable binder represents
the indispensable step in the development of ablation
– based methods. In our work we investigated a silica solgel
matter preparation and its mixing with soil samples. The
binder was then successfully applied in LA-ICP-OES/MS
methods. The accuracy of the developed methods was confirmed
by analysis of certified reference materials of soils
(GBW07405 – 07).
Experimental
S o i l S a m p l e s
Experimentally contaminated agricultural soils representing
various soil types belong to archived materials of the
Central Institute for Supervising and Testing in Agriculture
(UKZUZ), Brno, Czech Republic.
Studied trace elements Cr, ni, Cu, Zn, Pb occur in the
concentration ranges as shown in Table I.
The soil samples were ground in a ball mill and dried
to constant weight. The particle size of ground samples was
measured by laser diffractometry and the particle diameter
did not exceed 30 µm.
Table I
Concentration range of tested soils and RSD values for
Pn-ICP-OES
Element C range [mg kg –1 ] RSD [%]
Cr 21–590 3.7–1.7
ni 3.5–262 14–0.9
Cu 11–242 2.5–3.2
Zn 51–1355 2.7–0.5
Pb 22–1015 2.7–1.6
The solution analysis by ICP with pneumatic nebulization,
(Pn-ICP-OES) was carried out after the sample decomposition
with a mixture of HF and HClO 4 (ref. 5 ) The soil-wax
pellets for XRF analysis were prepared as a mixture of 4 g
of a soil powder and 0.9 g of wax. The mixture was homogenized
in a ball mill and then pressed by a hydraulic press
to a pellet with a diameter of 32 mm. Sequential extraction
was performed using five reagents with a different strength
(Table II) 8,9 . The sol-gel method, allowing homogenous dispersion
of internal standard (Sc) and analytes in calibration
pellets, was applied for analysis of tested soils by LA-ICP-
MS 10 .