Fluorescence excitation-emission matrix spectra of different sizes of dissolved organic matter produced by microalgae

The filtration and cross-flow ultrafiltration techniques were used to isolate the culture mediums of Heterosigma akashiwo and Skeletonema costatum into the retentate of 100 kDa-0.7 μm, 10-100 kDa and l-10 kDa and the ultrafiltrate of less than or equal 1 kDa. The different sizes of dissolved organic matter were detected by the three-dimensional fluorescence excitation-e-mission matrix spectrum. The peak, peak number and intensity of fluorescence in the spectra plots were analyzed. It is showed that the humic-like fluorescence substance was mainly composed of less than or equal l kDa molecules. The 15% of the proteinlike fluorescence substances produced by Heterosigma akashiwo were the macro-colloid of 100 kDa-0.7 μm, 8% were the mid-colloid of 10-100 kDa, and the most of them were the micro-molecule of less than or equal l kDa. Compared to the filtrate of Heterosigma akashiwo, the emission wavelengths of protein-like fluorescence peaks in the different sizes of ultrafiltration retentate were blue-shifted, but these in the ultrafiltrate were red-shifted, which suggested that the polarity was decoupled with the size increasing of the protein-like fluorescence substances produced by Heterosigma akashiwo.