Chemical and Spectroscopic Properties of Soil Hydrophilic Fulvic Acid Purified by Tangential Flow Ultrafiltration

Abstract

There is a growing recognition that unless soil hydrophilic fulvic acid (HiFA) is studied together with soil hydrophobic FA (HoFA), we will not fully understand the characteristics of the FA fraction in soils. The aim of this study was to characterize soil HiFA, which were extracted from soil and purified by tangential flow ultrafiltration (TFU), by means of elemental (C, H, O, N, S) and isotope (C-13, N-15) analyses, Fourier transform IR (FT-IR) and fluorescence spectroscopy and neutral sugars analysis. Results revealed marked differences between HiFA and HoFA in terms of chemical (elemental, isotopic and neutral sugar compositions) and spectroscopic properties (FT-IR, fluorescence spectra). The HiFA carbon accounted for 46 to 80% of the total FA carbon and thus, an important constituent of the FA fraction. On average, neutral sugars contents in HiFA is twofold larger than in HoFA and are mostly dominated by rhamnose, galactose, and fucose, while in HoFA, mannose was the most abundant neutral sugars, indicating that not only quantity, but also quality of neutral sugars varies between HiFA and HoFA. To further enhance the understanding of the characteristics and composition of soil HiFA including its turnover rate, fate and chemical transformation in soils, it is indispensable to isolate and purify HiFA. As such, purification of soil HiFA by TFU is satisfactory for such purpose.