C - Lublin

RESULTS AND DISCUSSION
The highest HAs yields were obtained by extraction with 0.1M NaOH (Table
1) while solid HS fractions extracted from NH with RSO 3 Na (Protocols 2 and 3)
were yellow and did not contain HA residues. Five HA fractions isolated with
RCOONa resin (C2 and C3) and 0.1M NaOH (A1, A2 and A3) have low ash
content and similar elemental composition (not shown).
Table 1. Steps of humic acids extraction procedures and some HAs characteristics.
Protocol Soil
№ pre-treatments
1 Benz.:meth., 2:1;
0.1M HCl
2 RSO 3 Na-H 2 O
Extractant used HAs
fraction
Yield, a
%
Ash b
%
0.1M NaOH, A1 8.3 0.66
RCOONa-H 2 O C2 2.2 0.46
RSO 3 Na-H 2 O;
RCOONa-H 2 O
3 Benz.:meth, 2:1;
RSO 3 Na-H 2 O
0.1M NaOH
RCOONa-H 2 O
A2
C3
4.3
2.7
0.54
0.22
Benz.:meth., 2:1;
RSO 3 Na-H 2 O;
RCOONa-H 2 O
0.1M NaOH A3 5.0 0.52
a,b
All data were averaged from two/three replications, a on a dry source weight
basis, b on a dry HAs weight.
Based on UV-visible characteristics (Table 2) resin-extracted HAs absorb
more UV light compared to alkali-extracted HAs. The latter (except A3) absorb
more strongly at λ = 665 nm, and have lower values of A 254 /A 436 and E 4 /E 6 ratios,
suggesting 7 a higher aromaticity and/or higher particle size of alkali-extracted
material.
The fluorescence emission spectra (Figure 1) of all HA fractions are
characterized by a broad band centered around 465 nm for resin extracted HAs and
between 450 and 460 nm for alkali-extracted ones. Alkali-extracted HAs exhibit
lower fluorescence intensities across the entire emission and synchronous spectra
(not shown) in respect to resin-extracted HAs, suggesting 6,7 that alkali-extracted
material contains higher amount of conjugated aromatic π-electron systems. The
fact that benzene:methanol pre-washing of soil has no effect on fluorescence
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