In 2012, a team of scientists used NMR spectroscopy to measure all of the position-specific carbon isotope abundances of glucose and other sugars. It was shown that the isotope abundances are heterogeneous. Different portions of the sugar molecules are used for biosynthesis based on the metabolic pathway an organism uses. Therefore, any interpretations of position-specific isotopes of molecules downstream of glucose have to consider this intramolecular heterogeneity.
Glucose is the monomer of cellulose, the polymer that makes plants and trees rigid. After the advent of position-specific analyses of glucose, biogeochemists from Sweden looked the concentric tree rings of a Pinus nigra that recorded yearly growth between 1961 and 1995. They digested the cellulose down to its glucose units and used NMR spectroscopy to analyze its intramolecular isotopic patterns. They found correlations with position-specific isotope enrichments that were not apparent with whole molecule carbon isotope analysis of glucose. By measuring position-specific enrichments in the 6-carbon glucose molecule, they gathered six times more information from the same sample.