AMMRL Members:
I have a question about implementation of bilevel WALTZ/CW decoupling on Bruker TopSpin 3.1. By default since I've been in the polymer industry, I have been using WALTZ-16 decoupling. However, when I am looking at a polymer using Si-29 NMR with a string of SiH groups, I am getting two spurious signals where I am trying to look for real signals. I tried experimenting with WALTZ-17, WALTZ-64, WALTZ-65, GARP, and BB decoupling. WALTZ-64 looks similar. WALTZ-17 and WALTZ-65 suppress these peaks in comparison but they are still present. GARP and BB do not result in these peaks but leave too many other spurious peaks removed by the WALTZ sequences.
I came across a 2007 JMR publication from Zhou, Kummerle, Qiu, Redwine, Cong, Taha, Baugh, and Winniford jointly from Bruker and Dow Chemical talking about this issue for polyethylene copolymers and the implementation of bilevel WALTZ and CW decoupling using bi_Waltz-65_64pl and bi_Waltz-65_256.
I tried switching my decoupling to bi_Waltz-65_256 from the "ased" panel but I didn't see any places where you chose the cw power level. Looking into the sequence, it looks like the pl from the CPD portion is multiplied by 1.3 or so (?).
Undecoupled my splitting is 243 Hz. When I implemented this sequence, I had severe broadening of Si not directly connected to H, and my SiH peak now showed a splitting of 52 Hz. And the overall S/N was actually worse than with no decoupling. I am guessing that I somehow implemented this bilevel decoupling incorrectly. Does anybody have any suggestions?
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James M. Gibson, PhD
Lead Analytical Scientist
Momentive Performance Materials
(518)233-3668
James.gibson_at_momentive.com
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Received on Thu Oct 23 2014 - 11:34:12 MST