An improved method to quantify bulk carbohydrate in marine planktonic samples

The TPTZ (2,4,6-tripyridyl-s-triazine) method is used to detect monosaccharides from seawater and particulate matter samples because it is sensitive, precise, rapid and easy to perform. Contrary to mechanisms proposed in the literature, we provide evidence that the TPTZ method detects hydroxyl as well as aldehyde groups in monosaccharides when all reducing groups are fully deprotonated in alkaline medium. We use this insight to develop an optimized hydrolysis protocol to increase yields from polysaccharides while minimizing the dehydration of monosaccharides. Compared to the TPTZ method with commonly used hydrolysis protocols and the often-used phenol–sulfuric acid method, our new optimized method detects a wider range of carbohydrates with a more consistent yield relative to glucose and much lower coefficient of variation. When applied to phytoplankton cultures and marine particulate samples, our new method achieves significantly higher bulk carbohydrate yields.