Results and Discussion 



Three samples of HA's were isolated from seawater that 

 was collected at Stations (50+53) and (69+74) in the Chukchi 

 Sea and at Station 1 12 in the Bering Sea. They were characterized 

 by the elemental analysis and spectroscopic studies. 



Elemental Analysis 



The results of elemental analysis of the HA samples are 

 summarized in Table 2. 



TABLE 2 



Elemental analysis of Humic Acids. 

 Sample Station %C %H %0 %S 



%Ash 



As can be seen from Table 2, the humic materials are 

 characterized by the high oxygen content (51-53%). which is 

 typical for marine HA in general (Brown, 1987; Alberts et al., 

 1988). The presence of sulphur may indicate the presence of 

 lignosulphonic acids (more or less biochemically degraded), 

 which are one of the precursors of humic acids. As a whole, the 

 humic materials isolated from the rather different environments 

 show many similarities in elemental composition. 



Spectroscopic Studies 



The IR spectra of the HA studied are rather similar (Fig. 1 ). 

 The broad band at about 3,400 cm ' and the inflection at about 

 2.600 cm ' are attributed to O-H stretching. The bands at 

 2,990 cm ' and 2,970 cm ' are due to C-H stretching. Carbonyl 

 stretching gives rise to bands at 1,620 cm ' (conjugated C = 0). 

 Signals from aromatic nuclei (skeletal vibrations) probably 

 both contribute to the latter band and are also responsible for 

 the band at 1,470 cm'. The complex band at about 

 1 , 1 20 cm ' presumably is due to C-O stretching of phenols and 

 alcohols. A fairly well defined band at 980 cm ' is primarily 

 attributed to aromatic C-H in-plane deformation. 



Finally, it should be pointed out that obtained IR spectra 

 exhibited strong similarities in general appearance with those 

 obtained by Paxeus ( 1985) and Dereppe et al. (1980). 



LU 



O 



z 

 < 



z 

 < 



QC 



4000 3000 2000 1600 1200 800 



Fig. I. IR-spectra of tlie isolated samples of humic acid. 



D, cm 



-1 



Ultraviolet and Fluorescence Spectra 



The UV spectra of the HA samples are shown in Fig. 2. 

 The spectra of aqueous solutions of HA do not exhibit 

 characteristics bands except for the shoulders at 210-230 nm. 



The fluorescence spectra of the HA samples are shown in 

 Fig. 3. The spectra show one broad band in the excitation 

 spectrum (310-330 nm) as well as in the emission spectrum 

 (400-420 nm). The fluorescence spectra of the HA agree with 

 those obtained by Hayase and Tsubota (1983) and Cabaniss 

 and Shuman( 1987). 



The pH-dependence of fluorescence intensity of the HA is 

 complex (Fig. 4). Fluorescence intensity is the highest at pH 

 values of 4-5. Decreases in the pH from 4 to 2 are followed by 

 a fall in fluorescence intensity by 5-10%. Raising the pH value 

 to 7.0-7.5 leads to a decrease in the intensity by 15-20%. 

 Further increase in pH value does not affect the fluorescence 

 intensity. 



LU 

 O 

 Z 

 < 

 CO 

 DC 



o 



m 

 < 



HA-2 

 HA-1 

 .HA-3 



200 250 300 350 



Fig. 2. UV-spectra of the isolated samples of humic acids. 



X, nm 



EXCITATION 

 HA! 



EMISSION 



200 250 



300 



350 



400 



450 



1, nm 



Fig. 3. Fluorescence spectra of the isolated HA samples. 



233 



