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Tham khảo tài liệu 'international perspectives on global environmental change part 12', khoa học tự nhiên, công nghệ sinh học phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | HPLC Fingerprints of Porewater Organic Compounds as Markers for Environmental Conditions 319 All chromatograms of L. Peipsi sediment pws were very similar consisting of two main peaks representing HMW and HS fractions. The intensities and positions of the peaks i.e. fractions changed in different sediment layers reflecting age-related changes in the concentrations and transformation of organic constituents. The area of the HMW fraction was always smaller 3 of the total area than the second HS fraction 97 of the total area . The calculated molecular masses for the HMW fraction varied between 200 and 270 kDa. The HMW fraction was absent from samples dating from the 1990s and from older samples from the nineteenth century. The HS fraction with molecular masses between 700 and 3 700 Da was dominant. The calculated average Mw was 1 500 Da which is characteristic for aquatic humic and fulvic acids. The profiles of the determined chemical characteristics and HPLC variables are presented in Fig. 4. The L. Rõuge Tougjarv pwDOM was also separated into two peaks. The components of the second peak eluted as a broad distribution and sometimes with a partially resolved subshoulder. Possibly the composition of the pwDOM from those sediment layers where the sub-shoulder appeared some layers from the 1980s and 1960s might have been somehow different from the major DOM composition. According to DAD spectra components eluted with the first peak contained proteinaceous material while the second peak spectra were characteristic of HS. The retention times of both peaks remained stable down the core. The calculated molecular masses for the HMW fraction varied between 800 and 1 000 kDa Mw . The HMW fraction varied between 6 to 13 of the total peak area and was thus present in a significantly higher amount than in L. Peipsi sediment pws. Possibly HMW material might have been formed from some proteins encapsulated into HS aggregates or micelles. The ability of HS to aggregate into large .
