Improved analysis of dissolved carbohydrates in stream water with HPLC-PAD

This paper describes improvements made to the determination of dissolved carbohydrates in stream water with high-performance liquid chromatography and pulsed amperometric detection (HPLC-PAD). We eliminated interference from dissolved oxygen, separated xylose and mannose along with other molecules, reduced the chromatographic peak shift associated with carbonate accumulation in the column to less than 1% for all samples, and achieved an 8% increase in recovery of hydrolyzed carbohydrates by replacing ion-exchange desalting cartridges with evaporative removal of HCl under N-2, These modifications lowered detection limits to less than or equal to 0.4 nM for 10 different monosaccharides and enhanced our ability to follow the dynamics of these molecules in stream ecosystems. In the determination of dissolved free monosaccharides, average relative precision was 1.3% and recovery ranged from 92 to 109%, For dissolved total saccharides, average relative precision was 3.3%. Concentrations were stable when filtered (0.2 mum) stream water was stored for 1 day at 22 degreesC, 1 week at 4 degreesC, or 1.5 months at -20 degreesC.