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.