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I recently calibrated the 90 for 11B on a Agilent 400MR. The 1H 90 was about 6.8us at 59dB... It turns out to be 22.6us for 11B at 59dB. Is this long enough that I should consider upping the pulse power? More generally, how long is too long a pulse in general? |
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Hi, 11B uses a different amplifier as 1H, thus different parameters as well. Check tpwr and tpwrm/tpwrf (if the latter is created). Both determine pulse power. Than check if u have a good match for the 11B frequency. If u keep having long pulses check it for 13C. Any problem in the X-amplifier must be repeated for all X-nuclei. You can try increasing the power (tpwr n tpwrm/tpwrf), but carefully. You better plug the amplifier to an oscilloscope through an attenuator and check power levels directly. Good luck... |
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... a pulse must be faster than the fastest interaction in your sample. If u have a solid sample u need to check the whole hamiltonian (except zeemann, ie CSA, j-coupling, dipole, quadrupole, paramag) and find your largest interaction (probably quadruploar or dipolar, several tens of kHz). On liq samples look only at the isotropic ones (chem shift n j-coupling, ppm range). |
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The Rabi Frequency (gamma B1) in kHz is 250/t90 when the pulse length is in microseconds. If your chemical shift dispersion is comparable or larger than the Rabi frequency, excitation of resonances far from the carrier frequency will be reduced, especially so for 180 degree pulses. |
I'm not sure of the details of your system (5mm vs 10 mm probe, inverse vs BB observe, amplifier power, etc.) but 22.6 us does seem a bit too long for 11B. I would expect something on the order of 12 - 15 us for 10 mm, maybe 8 to 10 us for 5 mm. Our 500: 5mm BBFO, 100W, 10us P90. - Kirk Marat (Jul 18 '12 at 07:22)