University of Ottawa NMR Facility Web Site

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Thursday, June 19, 2008

11B Background Signals

Unfortunately NMR probes and NMR tubes cannot be "transparent" for all of the isotopes one may want to observe. Depending on the NMR probe, it is very common to have background signals for 19F, 23Na, 27Al, 29Si, 65Cu, 10B and 11B. These background signals must be taken into account when interpreting NMR spectra. The background signal for 11B on a Bruker AVANCE 300 with a 5 mm broadband probe is shown in the figure below with several different types of NMR tubes commonly used for routine work in our laboratory. The probe was tuned before running each spectrum and the spectra were collected with proton decoupling. The left hand panel shows the background signal for the NMR probe and the other spectra show the combined background of the probe and the indicated NMR tubes. It is obvious that the magnitude and shape of the 11B background depends on the type of NMR tube used. It should be noted that all of the major NMR tube manufactures offer quartz NMR tubes which have little (if any) 11B background signal.

5 comments:

A Ghosh said...

What is the source of the 11B signal when no tube is inserted? Is it originating from the probe insert? Is it made of glass?

Glenn Facey said...

A Ghosh,

Thanks for the question. I am not 100% certain where the background signal originates in an NMR probe with no sample tube but I believe the it comes primarily from the insert. Another possible source I could imagine would be from any glass variable capacitors.

Glenn

Anonymous said...

Dear Glenn,

People in our facility tell us we do cannot do 11B NMR although we have a Bruker Broadband BBI probe. Is this really the case? Does it depend only on the probe?

Many thanks,
Best wishes,
Charlotte

Glenn Facey said...

Charlotte,
If you have a BBI probe, a console capable of providing the frequency for 11B, and a BB amplifier then you can observe 11B using the outer coil of the BBI probe.

Glenn

Craig Grimmer said...

Good morning all

On the acquisition side, the "depth" pulse sequence(V)/program(B) provides effective suppression of the background signal. On the processing side, backwards linear prediction can do the same.

Craig.