Title: Deuterium Naturally Present in Solvent and Site-Specific Isotope Population of Deuterium-Enriched Solute
Abstract: As the concentration of aqueous <TEX>$CD_3OH$</TEX> solutions was decreased, the OD peaks in <TEX>$^2H$</TEX> NMR spectra grew relative to the <TEX>$CD_3$</TEX> peaks. Isotope impurity for OH groups of <TEX>$CD_3OH$</TEX> and deuterium naturally present in water contributed to the OD peaks. Using these peak area data, the site-specific isotope populations of isotope enriched chemicals were measured. In addition, the method using both <TEX>$^1H$</TEX> and <TEX>$^2H$</TEX> NMR spectroscopy was demonstrated with neat <TEX>$CD_3OH$</TEX> to measure the site-specific isotope populations. The results indicate that although it represents only ~0.015% of hydrogen isotopes, the deuterium naturally present in solvents cannot be ignored, especially when the concentration of deuterium-enriched solutes is varied. Proton/deuteron exchange between methyl and methyl/hydroxyl groups was confirmed to be negligible, while that among hydroxyl groups was detectable.