Concentration and composition of dissolved combined neutral sugars (polysaccharides) in seawater determined by HPLC-PAD

Abstract

The purpose of this study was to examine concentrations and composition of polysaccharides in marine systems. To do so, we explored various procedures for hydrolyzing combined sugars, which would be compatible with high-performance anion-exchange chromatography and pulsed amperometric detection (HPLC-PAD). Hydrolysis in 0.85 M H2SO4 for 24 h gave the same or higher concentrations for natural samples as hydrolysis in dilute HCl or a 12 M H2SO4 pretreatment method. The 24-h hydrolysis was in general less efficient in hydrolyzing commercially available polysaccharides compared to the 12 M H2SO4 pretreatment method, but the methods gave similar concentrations for natural waters. These data indicate that the 24-h hydrolysis method without any pretreatment is adequate for most natural waters and that known standards may not be representative models for naturally occurring combined sugars. Total concentrations of neutral sugars in estuarine and deep oceanic waters ranged from 4 to < 0.02 μM, a range larger than observed by other carbohydrate analysis methods or for total dissolved organic carbon (DOC). Total concentrations of neutral sugars also decreased greatly with depth. These data suggest that dissolved combined neutral sugars are a reactive component of the DOC pool. The molecular composition of these combined sugars was generally similar for surface waters ranging from marsh effluents to oligotrophic oceanic waters; glucose, galactose, mannose + xylose (coeluted), and fucose were the dominant sugars. Our data suggest that the molecular composition of dissolved neutral sugars in surface waters is quite uniform throughout the ocean.