High resolution 13C DOSY: The DEPTSE experiment

High Resolution Diffusion-ordered Spectroscopy (HR-DOSY) is a valuable tool for mixture analysis by NMR. It separates the signals from different components according to their diffusion behavior, and can provide exquisite diffusion resolution when there is no signal overlap. In HR-DOSY experiments on 1H (by far the most common nucleus used for DOSY) there is frequent signal overlap that confuses interpretation. In contrast, a 13C spectrum usually has little overlap, and is in this respect a much better option for a DOSY experiment. The low signal-to-noise ratio is a critical limiting factor, but with recent technical advances such as cryogenic probes this problem is now less acute. The most widely-used pulse sequences for 13C DOSY perform diffusion encoding with 1H, using a stimulated echo in which half of the signal is lost. This signal loss can be avoided by encoding diffusion with 13C in a spin echo experiment such as the DEPTSE pulse sequence described here.

Graphical abstractThe resolution advantage of 13C detection over 1H detection in diffusion-ordered spectroscopy (DOSY) brings with it a commensurate sensitivity penalty. This can be reduced by combining polarization transfer with diffusion encoding by spin echo, doubling sensitivity compared to existing stimulated echo methods. In 13C detected DOSY there is a lot less overlap than in 1H DOSY, allowing the identification of component in more complex mixtures. DEPTSE can double the signal achieved in current 13C DOSY experiments by encoding diffusion in a spin echo rather than in a stimulated echo.Download high-res image (125KB)Download full-size imageHighlights► 13C DOSY offers a great resolution improvement over 1H DOSY. ► Using a spin, rather than a stimulated, echo can double sensitivity. ► The DEPTSE sequence combines polarization transfer with spin echo diffusion encoding.