STUDY OF THE INTERACTION OF AL(III) WITH A SOIL FULVIC-ACID IN THE ACID PH RANGE BY SELF-MODELING MIXTURE ANALYSIS OF SYNCHRONOUS FLUORESCENCE SPECTRAL DATA
Jcge. Dasilva et al., STUDY OF THE INTERACTION OF AL(III) WITH A SOIL FULVIC-ACID IN THE ACID PH RANGE BY SELF-MODELING MIXTURE ANALYSIS OF SYNCHRONOUS FLUORESCENCE SPECTRAL DATA, Analytica chimica acta, 349(1-3), 1997, pp. 23-31
The association of Al(III) with a soil fulvic acid (fua) was monitored
in the pH range of 2.5-5.0 by synchronous fluorescence (SyF) spectros
copy. Sets of spectra of 100 mg/l fua solutions obtained at increasing
Al(III) concentration (up to about 0.7 mM) at each pH (2.5, 3.0, 3.5,
4.0, 4.5 and 5.0) were preprocessed by the self-modeling mixture anal
ysis method SIMPLISMA, with inverted second derivative spectra in the
pure variable selection step, to determine the number and to calculate
the spectra and concentration profiles of the components. This proced
ure detected two major components at all pH values: (i) one shows an i
ncrease of fluorescence which corresponds to a fluorescent complex for
med between Al(III) and one of the binding sites of the fua; (ii) the
other shows a decrease of fluorescence probably due to the decrease of
the free concentration of a fluorescent binding site that complexes A
l(III) forming a complex that does not show fluorescence. Considering
the component that shows increase of fluorescence, conditional stabili
ty constants [log(K) with standard deviation in parenthesis] were esti
mated: pH=2.5, 4.5(3); pH=3.0, 4.6(3); pH=3.5, 4.8(2); pH=4.0, 5.2(1);
pH=4.5, 6.1(2); and pH=5.0, 6.2(3). These results show that the stabi
lity of the complexes between fua and Al(III) decreases markedly for p
H<4.5. This behavior may have an important influence on the changes of
the environmental speciation of Al(III) upon acidification.