Heteronuclear decoupling

Optimization independent heteronuclear decoupling at fast MAS

Heteronuclear decoupling is important to maximize resolution and improve sensitivity. Several decoupling sequences such as TPPM, SW_f-TPPM, SPINAL, XiX, AM-XiX and PISSARRO perform reasonably well but require careful experimental optimisation of at least one or more parameters. However, the optimised parameters are sensitive to experimental parameters. For samples with relatively high signal to noise, this is not an issue, and decoupling conditions can be  re-optimised. However, samples with poor signal to noise are standard in solid-state and in such cases, optimisation of each parameter is demanding. Therefore, there was a need for heteronuclear sequences that are practically optimization independent, especially in the fast MAS regime where detection of ¹³C and ¹⁵N signals is very insensitive.

In the fast MAS regime (40 kHz and above), we have designed two low-power heteronuclear decoupling sequences that are practically optimization independent. The two new heteronuclear decoupling sequences are a) low-power rCW^ApAand b) the refocused-XiX (r-XiX). The knowledge of the MAS frequency and approximate RF fields is sufficient to predict the necessary parameters for decoupling.