lace2003

1
Soil Organic Matter Studies necessity to
understand better the fate of pollutants and the
way to improve quality of risk assessment
Dagmar Gajdošová1, Eladia M. Peña-Méndez2 , Ma.
De Lourdes Pacheco H.3 and J. Havel11Department
of Analytical Chemistry, Faculty of Science,
Masaryk University, Kotlárská 2, 611 37-Brno,
Czech Republic 2 Department of Analytical
chemistry, Nutrition and Food Science, Faculty of
Chemistry, University of La Laguna, Spain 3
Universidad Autónoma del Estado de Hidalgo,
Centro de Investigaciones Químicas, Hidalgo,
Mexico
RESULTS AND DISCUSSIONS Soil organic matter (SOM)
represents the organic part of soil. It includes
high molecular weight organic material
(polysaccharides, proteins, etc.), small
molecules (amino acids, sugars, etc.) and humic
substances (humic acids, fulvic acids and humin).
Humic substances (HS), natural compounds widely
distributed in nature, play important role in the
environment. Several humic acids (HA) extracted
from soil of different sources and countries and
all continents, including Antarctica were
analyzed and characterized by MALDI-TOF mass
spectrometry and Capillary Zone Electrophoresis
(CZE). We have found, that extraction
process can be eliminated and by direct laser
ablation of soil mass spectra of low molecular
weight HA can be obtained. Spectra measured were
compared with those of extracted humic acids.
Additionally, also HA-xenobiotics (pesticides,
heavy metals, uranium etc.) interactions were
studied. The study was based on capillary
electrophoresis. The complexation of HA-
xenobiotics is strong. The interactions were
found to be of different kind depending on the
structure of the xenobiotic molecule and on its
charge (neutral, positive or negative). Metal
ions are strongly bound, but e.g. in case of
uranium several complexes are formed and it was
proved that at high excess of HA-uranium (VI) is
mobilized. Even such ions like chloride, nitrate
are partly bound to HA.

• Soil composition
• Mineral- inorganic (stones, gravel, sand, dust,
  clay)
• Organic matter 1. High molecular-weight organic
  material (polysaccharides, proteins)
• 2. Simpler
  substances such as sugars, amino acids, and other
  small molecules
• 3. Humic
  substances fulvic acids the fraction that is
  soluble in water under all pH conditions
• 
  humic acids - the fraction
  that is not soluble in water under acidic
  conditions (pH lt 2)
• 
  
  (lignin, polyphenols, proteins and amino acids,
  cellulose and other
• 
  
  polysaccharides)
• 
  humin - the fraction that is
  not soluble in water at any pH value and in
  alkali
• Water
• Gas
• Living organisms (gnathostoma, insects,
  bacteria, protozoa, fungi, algae).

MALDI-TOF MS
A Study of SOM and humic acids, especially
(capillary electrophoresis, mass spectrometry)
EXPERIMENT
Rapid characterization of soil low molecular
weight organic matter
MALDI-TOF MSMatrix Assisted Laser Desorption
-Ionization-Time Of Flight Mass Spectrometry is
a powerful tool for the determination of
molecular weightof biomolecules.
MODEL
Mass spectrum of Soil HA IHSS standard
Axima-CFR, MS MALDI TOF (Kratos Analytical,
Shimadzu Group Company, Manchester, United
Kingdom)
Mass spectra modeling of a group of the peaks
around m/z 813.4 ?MH? (at least 5 compounds
with a similar structure are presentPossible
combination of empirical formulas m/z 810. 42
C45H62O13 , 811.43 C45H63O13 , 812.43
C45H64O13 , 813.44 C45H65O13 , 815.46
C45H67O13


A humic acid extracted from pine forest (La
Esperanza, Tenerife, Spain)B soil from pine
forest (La Esperanza, Tenerife, Spain)

• Mass spectra of low molecular weight organic
  matter can be obtained rapidly by direct soil
  ablation (extraction procedure is eliminated).
• Mass spectra modelling shows complexity of mass
  spectra, some empirical formulas are proposed (HA
  are low molecular weight and contain at least
• several hundreds of compounds).

Fig. A
B. Study of humic acids interactions with
xenobiotics (insecticides p,p-DDT, p,p-DDE,
Paraquat, Diquat
toxic inorganic compounds, nitrate,) heavy
metal ions interaction (Hg (II), Cu (II), Cd,
uranyl, etc).
Capillary zone electrophoresis (CZE)
Beckman (Model PACE) System 5500 (Palo Alto, CA,
USA) equipped with diode array detection (DAD)
system, automatic injector, fluid cooled column
cartridge and System Gold Data station. Fused
silica capillary tube of 37 cm (30.5 cm to the
detector) y 75 um I.D. was used.

Example of toxic metal interaction with humic
acids POSITIVE UO22- HA SPECIES UO2 2tot
0.2 mM / HAtot1.6 mM, pH 4
Fig. B
Fig. C
A Migration of UO22-(CO3)-HA species increasing
HAtot UO22 tot 5 mM, carbonate buffer 20
mM, pH 10.5 B Migration of UO22- (CO3) -HA
species at various UO22tot HAtot5 mM,
carbonate buffer 20 mM, pH 10.5
Electropherograms of humic acids extracted from
soil of various origin Conditions background
electrolyte BTE (pH 8.5)

• The complexation of HA-uranium (VI) leads to
  several complexes, uranyl migrates as cationic
  species at low HA concentration (Fig. A) .
  Electrophoretic mobilites are
• decreasing with increasing HA concentration. At
  HA higher than 3 mM negatively charged uranium
  species is formed. However, migration of UO2 2
  depends also on
• carbonate content in system (Fig. B, C).
• Study of HA interaction with organic and
  inorganic xenobiotics shows that it is of various
  kind (complexation, adsorption, intercalation,
  supramolecular complexation,
• etc.) and it is quite different for each
  xenobiotics.

CONCLUSION These results should be taken into
account for evaluation of risks and proposal of
adequate soil (sediments) remediation.
REFERENCES 1 D. Gajdošová, K. Novotná,
P.Prošek and J. Havel Separation and
characterization of humic acids from Antarctica
by capillary electrophoresis and MALDI TOF mass
spectrometry. Inclusion complexes of humic acids
with cyclodextrins, J Chromatogr A, (2003),
1014. 2 D. Gajdošová, L. Pokorná, K. Láska , P.
Prošek, J. Havel Are there humic acids in
Antarctica? in Humic Substances Structures,
Models and Functions, Cambridge RSC, (2001). 11
s. 3 M.L. Pacheco, E. M. Peña-Méndez, J.
Havel Supramolecular interactions of humic
acids with organic and inorganic xenobiotics
studied by capillary electrophoresis ,
Chemosphere 51 (2003) 95-108 4 E. M.
Peña-Méndez, D. Gajdošová, K. Novotná, P. Prošek
and J. Havel Mass Spectrometry of Humic
Substances of different origin including those
from Antarctica. A comparison study (Talanta
11/2004  )