Thursday, March 27, 2008
What is the Difference Between a Broadband and an Inverse Broadband Probe?
I am sometimes asked, what is the difference between a broadband probe and an inverse broadband NMR probe? Both probes typically have a fixed proton channel, a tunable broadband channel and a fixed 2H lock channel. The difference lies in the coil positions with respect to the sample. Broadband probes are optimized to observe an X nucleus (typically all nuclei with frequencies between 15N and 31P). The broadband, X coil is positioned closest to the sample to maximize the filling factor and hence the X nucleus sensitivity. The 1H coil is outside of the X coil and can be used for either 1H observation or 1H decoupling. The filling factor for this coil is lower than that of the X coil. In an inverse broadband probe, the 1H coil is closest to the sample maximizing the 1H sensitivity. The X coil is outside of the 1H coil and can be used for either X nucleus observation or decoupling. The X nucleus in an inverse broadband probe has much less sensitivity than in a broadband probe. The choice of probe depends entirely on whether the user desires more 1H or more X sensitivity. For example, The 13C spectra of dilute samples should be run in a broadband probe whereas 1H - 13C or 1H - 15N HSQC spectra of dilute samples should be run in an inverse broadband probe.