ionization- and reduction-difference spectra of humic and fulvic acids
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Ionization- and Reduction-Difference Spectra of Humic andFulvic AcidsKyoichi Kumada aa Faculty of Agriculture, Nagoya University , Nagoya , Aichi ,464 , JapanPublished online: 30 Oct 2012.
To cite this article: Kyoichi Kumada (1985) Ionization- and Reduction-DifferenceSpectra of Humic and Fulvic Acids, Soil Science and Plant Nutrition, 31:3, 449-461, DOI:10.1080/00380768.1985.10557452
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Soil Sci. Plant Nutr., 31 (3), 449-461, 1985
IONIZATION- AND REDUCTION-DIFFERENCE SPECTRA OF HUMIC AND FULVIC ACIDS
Kyoichi KUMADA
Faculty of Agriculture, Nagoya University, Nagoya, Aichi, 464 Japan
Received September 28, 1984
The ionization difference (LlE,) and reduction difference (dEr) spectra of humic acids (HAs) and fulvic acids (FAs) were determined. In the present study, .JE, and .JE, spectra refer to the difference spectra between the pH 13 and pH 6 solutions and between the pH 10 and NaBH,treated pH 10 solutions, respectively.
The .JE, spectra of 9 out of 17 samples showed absorption bands due to the 4·9-dihydroxyperylene-3.10-quinone moiety. Based on the .JE, spectra, the samples were divided into 4 groups. This grouping was approximately the same as that based on the .JEr spectra.
The contribution of the .JE, and .JEr spectra to the ordinary absorption spectra was discussed. Key Words: fulvic acid, humic acid, ionization difference spectrum, reduction difference spectrum.
Differential spectral techniques have been widely used in lignin chemistry (1). There have been several reports (2, 8-10) on the difference spectra of soil humic acids (HAs), which suggest that difference spectra are useful for differentiating soil humic substances from one another. To confirm this, the ionization difference (JE1) and reduction difference (JE,) spectra of the HAs and fulvic acids (FAs) used in the previous paper (6) were determined.
In the present study, the JE, and JE, spectra refer to the difference spectra between the pH 13 and pH 6 solutions and between the pH 10 and NaBH~-treated pH 10 solutions, respectively.
MATERIALS AND METHODS
HA and FA samples. Seven HAs and 10 F As samples were used. Their origins, methods of preparation, elementary composition and absorption spectra in the UV and visible regions were reported in ~he previous paper (6):
Determination of JE, spectra. Sample solutions containing S to 40 mg of HA or FA in 100 ml of 0.1 N NaOH were prepared according to the procedure described in the previous paper (6). Ten ml of the sample solution was pi petted into a 2S ml volumetric flask, and the flask was filled up to volume with 0.1 N NaOH. This solution was designated as the pH 13 solution. Another 10 ml aliquot of the sample
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450 K.KUMADA
solution was adjusted to pH 6.0 with dilute phosphoric acid (1: 9), and the pH 6 solution prepared by adding phosphoric acid to 0.1 N NaOH was added to make a total volume of 25 ml.
The AE, spectra from 230 to 700 nm were obtained by determining the difference in the optical density between the pH 13 solution and pH 6 solution. The values obtained were plotted in the form oflog JE1 vs. ;. curves. JE11% values at selected wavelengths were calculated, where JE11% is the difference in the optical density of the solution containing 1% HA- and FA carbon. The determination was conducted immediately after the preparation of sample solutions using a Shimadzu UV-240 Spectrophotometer.
Determination of AE. spectra. Ten ml aliquots of the sample solution were placed in 2 beakers, and the pH was adjusted to 10.0 with phosphoric acid. After the addition of solid NaBH, corresponding to about 10 times the amount of the sample weight to one of the beakers, the volume of both solutions was adjusted to 25 ml with the pH 10 solution prepared by adding phosphoric acid to 0.1 N NaOH.
The JE. spectra from 230 to 700 nm were obtained by determining the difference in the optical density between the pH 10 solution and NaBH,-treated pH 10 solution, 24 h after the addition of NaBH,. The values were plotted in the form of log JE. vs. ;. curves, and JE.l% values at selected wavelengths were calculated.
RESULTS AND DISCUSSION
As reported previously (6), the ordinary absorption spectra of 5 out of the 17 samples showed absorption bands attributed to the dissociation of the 4· 9-dihydroxyperylene-3·10-quinone (DHPQ) moiety referred to as Pg absorption. As for the other samples, the absorption curves were smooth, and it was difficult to find any quantifiable features. However, their spectral characteristics varied with the samples, as revealed by the E81% (EJ&nm), E,/E8 (E4oonm/E6oonm) values and other parameters.
AEl spectra Figure 1 and Table 1 show the AE 1 spectra of samples and AE 11% values of prom
inent absorption bands, respectively. First, absorption bands in the visible region will be dealt with. In the absorption
curves of samples #3 HA and FAl and #6 HA, FAl and FA2, the absorption bands at around 615, 565 and 460 nm, corresponding to Pg absorption, were more distinct than in the ordinary absorption curves reported previously (6). Besides, the bands at 530 and 430 nm in #6 HA and a band at 520 nm in #3 HA were also attributed to Pg absorption, because the Pg fractions (01, O2 and Os) (4) separated from #6 soil showed these bands too.
Pg absorption was observed in the AE1 spectra of samples #1 P, #2, #4 and #5 HAs which did not appear in the ordinary absorption spectra (6), as was previously noted by TSUTSUKl and KUWATSUKA (9).
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Ionization- and Reduction-Difference Spectra 4'1
Table 1. ..1El1% values of main absorption bands.
Sample 250nm 290nm 33'nm 370nm 460nm 565nm 61'nm (245-250) (28'-298) (33(}-340) (35'-390) (4S(}-48') (56(}-'70) (61 (}-620)
#1 OH HA 47.8 31. 8 4'.2 (10) & (8) (22)
FA 12.9 9.2 14.0 (') (6) (11)
#1 P HA 68.4 '4.0 36.3 29.8 28.6 (9) (10) (17) (28) (35)
FA 13.6 1'.7 18.1 9.8 (4) (I') (14) (26)
#2 HA 56.7 66.1 59.2 21.6 20.2 (7) (10) (14) (32) (34)
FA 23.4 34.8 (4) (21)
#3 HA 20.9 66.5 46.9 58.8 34.3 20.2 24.8 (3) (11) (21) (23) (25) (34) (51)
FAl 13.3 27.0 37.6 43.2 18.3 9.3 8.8 (3) (8) (17) (30) (30) (41) (59)
FA, 13.8 25.3 44.9 48.2 (2) (6) (17) (30)
#4 HA '4.9 46.5 44.0 44.' 13.0 10.7 (10) (12) (18) (26) (40) (46)
FAl 33.8 36. 1 38.0 (8) (1') (27)
FA, 30.0 41.1 4'.7 (S) (19) (29)
#5 HA 39.3 58.1 SI. 8 33.8 29.1 26.5 (S) (8) (l0) (17) (27) (33)
FA 6.4 18.3 28.4 24.3 (2) (7) (18) (24)
#6 HA 149 41. 5 38.9 78.9 28.6 53.8 (26) (13) (17). (24) (34) (64)
FAl 40.1 26.4 32.0 18.3 9.8 12.2 (12) (16) (22) (28) (38) (64)
FA. 34.4 45.0 48.1 19.5 6.9 5.0 (8) (19) (2') (37) (49) (63)
& Figures in parentheses are the ratios (X) of ..1El1% to El% at the same wavelength.
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452 K.KUMADA
SATO (7) prepared alkaline solutions consisting of a purified Pg fraction and various HAs showing no Pg absorption, and determined their absorption spectra. In the case of one Rp type HA having a high E,/ E6 ratio, Pg absorption was detected when the Pg content was 2%. In an A type HA having a low E,/E6 ratio, however, shoulder-like absorption bands were observed only when the Pg content exceeded 6%. This finding suggests that Pg absorption can be observed only when the Pg content exceeds a certain level, and the lower the E,jE6 ratio of HA, the higher is the level necessary for the Pg fraction to be detected. This is the limitation of the method proposed by Sato for estimating Pg content, as he himself pointed out. In any case, the fact that the dEL spectra of the HAs having lower E,/ E6 values showed Pg absorption can be explained on the basis of the experimental results obtained by Sato.
The dEll% values at 615 nm for samples #6 HA, FAI and FA2 and #3 HA and FAI approximately corresponded to their Pg contents reported in the previous paper (6). However, the dEll% values at 615 nm for #1 P, #5 and #2 HAs were comparable to that of #3 HA. Thus Sato's method, undoubtedly, has limitations, and a new
Wavelength. nm
Fig. 1·1. JEl spectra (group 1).
Wavelength. nm
Fig. 1·2. JEl spectra (upper, group 2; lower, group 3).
700
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Ionization- and Reduction-Difference Spectra 453
Wavelength. nm Wavelength. nm
Fig. 1-3. .1El spectra (group 4). Fig. 2-1. .1E. spectra (grOUP 1).
method should be explored for estimating Pg content. Nevertheless, it is worth noting that 6 out of 7 HAs and 3 out of 10 F As showed Pg absorption in the LIEI spectra. This finding suggests the universal existence of the Pg fraction in soil humic substances.
Except for the samples mentioned above, #1 P FA and #5 FA each showed an absorption band near 485 and 470 nm in the visible region, respectively, suggesting the presence of special kinds of dissociated groups.
In the UV region, there were a number of absorption bands, but most of them were broad and overlapped with each other. Thus iL was rather difficult to determine exactly the positions of peaks and shoulders.
In sample #6 HA, absorption bands were observed at 283, 330, 360 and 400 nm, and the band at 283 nm was the strongest among them. It is not certain whether all of these bands are due to the dissociation of the DHPQ moiety. In general, the absorption bands found in the UV region of the LIEl spectra of the samples showing Pg absorption in the visible region may be due to the dissociation of the DHPQ moiety as well as of other groups, and it is at present hardly possible to distinguish them from one another. For example, the LIEll% values at 285 nm tended to become larger along
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o 2~20~~~--~~--~----~--~700
\ravelength, nm
Fig. 2·2. AE~ spectra (upper, group 2; lower. gt:0up 3).
700 Wavelength. nm
Fig. 2·3. LJE~ spectra (upper. group 2; lower, exception).
with those at 615 nm, but the band at 285 nm was also found in the samples showing no Pg absorption in the visible region. Therefore, the 285 nm band is probably due not only to DHPQ but also to other dissociated groups. The dEII% values of the bands at 360 nm bore no relation to those at 615 nm, suggesting that this band is not due to dissociated DHPQ. The same assumption may be valid for the band at 250 nm, because #6 samples did not show it.
With respect to the dEl spectra, the samples were tentatively divided into the following 4 groups, as listed in Table 2.
Group 1: Samples #6 HA, FAI and FAs and #3 HA and FAI. They are characterized by the presence of bands at 285 and 365 nm as well as Pg absorption in the visible region of dEl spectra and in ordinary absorption spectra.
Group 2: Samples #1 P HA, #5 and #2 HAs. They showed Pg absorption in the visible region of dEl spectra and had 3 bands at 285, 335 and 245 nm. The dEl values of these bands decreased in this order, and #1 P HA did not show the band at 245 nm.
Group 3: Samples #1 OH HA and FA and #1 P FA. They had fairly distinct absorption bands near 250, 290 and 355 nm. The shapes of their dEl spectra were
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Ionization- and Reduction-Difference Spectra 455
Table 2. Groupings of the samples based on JEl and JEr spectra.
Grouping a based on
Sample Esl% E,/E, Pg
(Yc,) .dEl .dEr Origin spectrum spectrum
#1 OH HA 23.8 5.6 0 3 3 Chernozemic Ah
FA 3.8 10.2 0 3 NDb
#1 P HA 88.9 3.4 0 2 2
FA 13.4 6.3 0 3
#2 HA 62.8 4.2 0 2 2 Solonetzic Ah
FA 9.7 10.6 0 4 4
#3 HA 46.2 4.0 1.8 Podzolic Bhf
FAl 17.1 7.0 0.08
FAI 12.1 10.8 0 4 4
#4 HA 24.8 5.8 0 4 4 Cryosolic Ah
FAl 17.5 7.2 0 4 4
FA, 13.5 10.6 0 4 4
#5 HA 86.2 3.4 0 2 2 Andosol Al
FA 13.4 6.9 0 4 3
#6 HA 76.2 2.4 7.8 1 Muck-like buried humic
FAl 19.5 5.3 1.0 1 layer
FA, 10.S 10.6 0.08
a See text. b Not determined. C Excluded from any group.
similar to those of lignin and Rp type HAs reported by KOBO and FUJISAWA (2) and TSUTSUKI and KUWATSUKA (9).
Group 4: The rest of the samples, #2 FA, #3 FA2, #4 HA. FAl and FA2 and #5 FA, were included in this group.
Sample #4 HA showed Pg absorption in the dEl spectrum, but its dE11% value at 615 nm as well as E81% value was small, and the shape of its dEl spectrum in the UV region was different from those of the HAs belonging to group 2. The dEl spectrum of this HA may be described as a composite of those of #4 FAl and the Pg fraction. With the exception of #4 HA, the samples belonging to group 4 were all FAs, and had a common absorption band at 245 nm as well as 2 or 3 bands in the region of 290 to 390 nm. At present, it is difficult to characterize them further.
TSUTSUKI and KUWATSUKA (9) demonstrated that the JE l spectra of A, D, Rp and P type HAs, according to the classification system proposed by KUMADA et al. (3). were different from one another. Groups 1. 2 and 3 described above may cor-
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456 K.KUMADA
respond to P type, A type and Rp type, respectively. Sample #4 HA in group 4 may correspond to B type. Out of the 7 HAs studied by Kono and FUJISAWA (2), numbers 5 and 2 seem to correspond to groups 3 and 2, respectively.
The experimental conditions adopted by the author, Kono and FUJISAWA (2) and TSUTSUKI and KUWATSUKA (9) were different with respect to the composition and pH of medium, but the results obtained were comparable, indicating that LlE, spectra are useful for differentiating soil humic substances from one another.
In lignin chemistry, LlE, spectra are interpreted in terms of various kinds of phenolic hydroxyl groups present. As precisely discussed by TSUTSUKI and KUWATSUKA (9), the LlE, spectra of the HAs belonging to group 3 and Rp type may be interpreted in terms of lignin chemistry to a certain extent, but there exist considerable differences in the LlE, spectra between lignin and the HAs mentioned above. The LlE, spectra of the other HAs are remarkably different from that of lignin. Therefore, the interpretation of the LlE, spectra should be left to future investigation.
LlEr spectra The LlEr spectra of the samples except #1 OH FA are shown in Fig. 2, and the
LlErl% values of their prominent absorption bands and the reference points selected, 460 and 560 nm, are listed in Table 3.
As mentioned above, LlE, spectra enabled us to divide the samples into 4 groups. Accordingly, it may be reasonable to examine whether this grouping is also applicable to LlEr spectra.
Group 1: In the visible region, samples #6 HA and F Al and #3 HA showed 2 absorption bands near 460 and 570 nm. These bands correspond to the shoulder-like bands observed in the ordinary absorption spectra of #6 HA determined at pH 10 in the previous paper (6). Thus they are attributed to Pg absorption. In samples #6 FAa and #3 FAl, only a weak shoulder band near 460 nm was observed, probably due to the low Pg content.
In the UV region, samples #6 HA, F Al and FAll showed 3 bands at 250, 280 and 320 nm, but for samples #3 HA and FAl, 2 bands were observed near 310 and 280 or 260 nm. Judging from the shapes of the LlEr spectra, the third band in #3 HA and FAI might have overlapped with the adjacent bands.
Group 2: Sample #1 P, #2 and #5 HAs belonged to this group. The LlErl% values at 280 and 315 nm were large. The curves were very broad, and the plateau-like absorption extended to 450 nm and further, judging from Fig. 2 and the LlErl% values at 460 and 560 nm. It is assumed that the HAs belonging to this group contain some carbonyl groups which affect light absorption throughout the whole UV and visible region. The Pg fraction revealed in the LlE, spectra may partly account for the strong light absorption in the visible region.
Group 3: Samples belonging to this group were characterized by lignin-like LlE, spectra. The LlEr spectrum of sample #1 OH HA was very broad and consisted of a peak at 320 nm and a shoulder near 280 nm. Sample #5 FA may be included in this
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Ionization- and Reduction-Difference Spectra 457
Table 3. LlErl% values of main absorption bands and at 460 and 560 nm.
Sample 250nm 280nm 315nm 46Onm& 56Onm& (247-260) (278-285) (310-320)
#1 OH HA 54.4 62.8 29.3 14.0 (12) c (20) (41) (42)
FAb
#1 P HA 98.6 91. 0 84.4 50.4 (12) (14) (40) (42)
FA 60.0 21. 9 9.4 (17) (45) (45)
#2 HA 71. 0 79.9 56.7 31.0 (10) (15) (33) (37)
FA 50.8 76.5 25.3 8.2 (10) (27) (51) (51)
#3 HA 59.4 68.5 39.3 22.0 (10) (16) (34) (38)
FAl 44.8 77.5 33.6 14.5 (12) (30) (51) (59)
FAI 85.0 112 32.7 11.5 (14) (30) (55) (60)
#4 HA 45.4 69.5 36.8 17.3 (9) (26) (45) (49)
FAl 37.8 77.3 35.4 15.6 (8) (30) (51) (59)
FAI 45.7 113 40.2 15.4 (14) (35) (57) (63)
#5 HA 87.4 84.3 60.3 34.9 (12) (14) (30) (31)
FA 46.6 48.3 22.3 9.1 (16) (21) (41) (45)
#6 HA 72.2 61. 0 46.4 86.4 46.4 (12) (10) (13) (48) (56)
FA, 39.5 47.4 43.S 33.9 14.1 (11) (14) (19) (46) (54)
FA. 74.1 87.2 80.6 28.3 8.4 (12) (18) (27) (49) (SI) .
a LlEr values at 460 and 560 nm were included for comparison. b #1 OH FA was not determined be-cause of the shortage of sample. D Figures ill parenthesis are the ratios (X> of LlErl% to El% at the same wavelength.
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458 K.KUMADA
group, because the shape of the JEr spectrum was similar to that of #1 OH HA. But #1 P FA should be excluded from this group, because it showed only 1 peak at 280 nm.
Group 4: Except for #5 FA, the samples belonging to this group, #2 FA, #3 FA i ,
#4 HA, FA! and FAs, were characterized by the 2 absorption bands near 315 and 250 nm, and the former was stronger than the latter.
As seen in Table 2, groupings based on JEI and JEr spectra were almost the same, except that sample #5 FA moved from group 4 to group 3 with respect to JEr spectra, and #1 P FA was excluded from any group.
According to this table, the following can be pointed out. (1) The HAs and FAs showing Pg absorption belonged to group 1. (2) Samples #1 P, #2 and #5 HAs having larger E61% values and lower £,/E6 ratios constituted a group, in which the FAs obtained from the same soils were not included. On the other hand, #1 OH and #4 HAs having smaller £81% values and higher £'/£8 ratios belonged to the same groups as the FAs obtained from the same soils, suggesting structural similarities between the HAs having a lower degree ofhumification and the FAs.
TSUTSUKl and KUWATSUKA (10) determined the JEr spectra of several HAs and pointed out the similarity between B and Rp type HAs and lignin. They stated that the JEr spectra of the milled wood lignin of rice straw and the Bjorkan lignin extracted from Picea abies by Adler and Martin had a maximum absorption at 320 nm and a shoulder at 340 nm. But sample #1 OH HA which exhibited a lignin-like JEI spectrum had 2 bands near 315 and 280 nm, differing from those of the lignins that they reported. It should be noted that TSUTSUKI and KUWATSUKA (10) used a buffer solution, and Na phosphate solution was used in the present study, although the pH of both solutions was 10. On the other hand, groups I and 2 seem to correspond to the P and A type HAs reported by TSUTSUKI and KUWATSUKA (10), respectively.
According to the results obtained in the present study, the JEr spectra of HAs and F As are characterized by the presence of absorption bands at 315 nm as wen as 250 and/or 280 nm, and in some HAs, the strong light absorption extended to the visible region. Even if it is almost certain that these bands result from various kinds of carbonyl groups, their chemical structures should be elucidated in the future.
Contribution of JEI and JEr to E Humic substances are characterized by their dark colour, i.e. appreciable light
absorption in the visible region which increases with the decreasing wavelength. But we know little about the mechanisms of light absorption. It is expected that absorption spectroscopy will serve as a means to solve this problem.
It has been said in lignin chemistry that JE1 and JEr spectra are associated with the presence of various kinds of phenolic hydroxyl and carbonyl groups, respectively. Although it is at present uncertain to what extent this interpretation is applicable to humic substances, the present study confirmed that their light absorption in the visible
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Ionization- and Reduction-Difference Spectra 459
region was reduced considerably by lowering the pH of the solution and by adding NaBH" to the solution.
To estimate the contribution of AEI and AEr spectra to ordinary absorption spectra quantitatively, the ratios of dEl and AEr values to E values at various wavelengths were calculated. The results are included in Tables 1 and 2. It is noted that Beer's law holds for AEI and AE~ as well as E values.
As seen in the tables, the dEllE and dEr/E values were similar to each other. Both ratios tended to be very low in the shorter wavelength region, increasing with the increase in wavelength, and reaching 33 to 64% for the AEI/E values and 31 to
Table 4. Contribution of dE 1 and dEr to E in the visible region.
Sample 400nm 500nm 600nm Sample 400nm 500nm 600nm
#1 OH HA la 22 24 34 #4 HA I 30 32 43
n 28 41 39 n 33 49 45
m so 65 73 m 63 81 88
#1 P HA I 14 20 32 FAl I 30 33 39
n 27 44 41 n 38 58 ss m 41 64 73 m 68 91 94
FA I 17 28 42 FA. I 32 36 40
II 32 47 40 n 46 62 60
m 49 75 82 m 78 98 100
#2 HA I 19 25 33 #5 HA I 15 20 30
n 24 36 35 n 22 31 30
m 43 61 68 m 37 SI 60 FA I 30 34 39 FA I 26 32 42
n 40 53 45 II 33 44 43
m 70 87 84 m 59 76 85
#3 HA I 27 21 40 #6 HA I 20 13 46
n 23 37 34 n 31 60 47 m SO 58 74 m 51 93 93
FAl I 32 32 46 FA1 I 25 29 47
II 38 57 56 n 35 51 49
m 60 89 102 m 60 90 96 FA. I 35 34 -39 FA. I 35 42 56
n 43 60 55 n 40 51 59
m 78 94 94 m 75 93 105
& I. dEllE; IT. dErlE; m. I + IT (%).
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460 K.KUMADA
63% for the JEr/E values. In the case of samples showing Pg absorption in the visible region, the JEl/E ratios at 460, 565 and 615 nm were in the ranges of 17 to 37%,27 to 49% and 33 to 64%, respectively, and the values obtained for FAs tended to be higher than those for HAs. The JEr/E values at 460 and 560 nm ranged between 30 to 57% and 31 to 63%, respectively, and the values obtained for FAs were higher than those for HAs. These results distinctly show that the contribution of JEl and JEr spectra to ordinary absorption in the visible region is quite large. This is confirmed further in Table 4, in which the values of JEl/E, JEr/E and the sum at 400, 500 and 600 nm are listed.
According to this table, the following can be pointed out. (1) In most cases, the JEr/E values were higher than the JEl/E values at each wavelength. (2) Both values tended to increase with the increase in wavelength. (3) The sum of JEl/E and JE,/E values at 400 nm ranged from 37 to 63% for HAs and 49 to 78% for FAs. The sum of values at 500 and 600 nm was either nearly equal or the latter was higher than the former. The sum of JEl/E and JEr/E at 600 nm ranged from 60 to 88% for HAs, and from 82 to 105% for FAs. Thus a large part of the light absorption in the visible region of HAs and FAs can be attributed to JEl and JEr.
The DHPQ structure observed in 9 out of 17 samples may be responsible for both the JEl and JE,. In the case of the HAs having high Ei% values, i.e. samples #1 P, #2 and #5 HAs, light absorption unrelated to JEl and JEr should not be overlooked. Part of this may be attributed to the graphite-like structure (5) confirmed for #1 P and #5 HAs (unpublished data).
The results obtained in the present study clearly show that JEl and JE., spectra are not only useful for differentiating individual soil humic substances, but also helpful in explaining their dark colour, i.e. specific light absorption in the visible region. Further investigation is necessary to interpret the diverse absorption bands in these spectra.
Acknowledgments. The author wishes to thank Prof. L.E. Lowe, the University of British Columbia, for many helpful discussions and suggestions during this work.
REFERENCES .
J) NAKANO, J. (ed.), Lignin Chemistry, Uni Publishing Co., Tokyo, 1982. pp. 169-173, 429-430 (in Japanese)
2) KOBO, K. and FUJISAWA, T., Studies on humus-clay complexes. 11. Preparation and properties of humic acids, J. Sel. Soil Manure. Jpn., 33,97-100 (1962) (in Japanese)
3) KUMADA, K., SATO, 0., OHSUMI, Y., and OHTA, S., Humus composition of mountain soils in central Japan with special reference to the distribution of P type humic acid, Soil Scl. Plant Nutr., 13, 151-158 (1967)
4) KUMADA, K. and SATO, 0., Characteristics of the green fraction of P type humic acid, Soil Set. Plant Nutr., 26,309-316 (1980)
5) MATSUI, Y. and KUMADA, K., An X-ray diffraction study of humic acid, Soil Scl. Plant Nutr., 30, 13-24 (1984)
6) KUMADA, K., Elementary composition and absorption spectra of humic and fulvic acids, Soil Sel. Plant Nutr., 31, 437-448 (1985)
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7) SATO, 0., Methods for estimating Pg content in P type humic acid and for calculating .dlog K of its Pb fraction, Soil Sei. Plant Nutr., 20, 343-351 (1974)
8) SUZUKI, M. and KUMADA, K., Several properties of Rp type humic acid, Soil Set. Plant Nutr., 18, 58-64 (1972)
9) TSUTsUIa, K. and KUWATSUKA, S., Chemical studies on soil humic acids. VII. pH-dependent nature of the ultraviolet and visible absorption spectra of humic acids, Soil Set. Plant Nutr., 25, 373-384 (1979)
10) TSUTSUKI, K. and KUWATSUKA, S., Chemical studies on soil humic acids. VIII. Contribution of carbonyl groups to the ultraviolet and visible absorption spectra of humic acids, Soil Sei. Plant Nutr., 25, 501-512 (1979)
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