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Thursday, October 18, 2007

Proton Probe Tuning for 13C Detected Experiments

I am sometimes asked: Do I have to tune the proton channel of the probe for my 13C detected experiments? The answer is yes. If you are just running a simple 13C with proton decoupling then the efficiency of the decoupler will depend on the tuning of the proton channel. If the proton channel of the probe is very badly tuned, you may see broadening and even splittings in your carbon signals. The signal-to-noise ratio will also suffer. For experiments like DEPT or INEPT, the proton tuning is critical as these sequences require proton pulses of specific flip angles. If the proton channel of the probe is not tuned and matched then the flip angles for the proton pulses in the sequence will be less than they should be and you will not get the results you expect. In the figure below is an example. The bottom trace is a 13C DEPT-135 spectrum of menthol with the proton channel of the probe properly tuned. The spectrum in the upper trace is also a DEPT-135 spectrum of menthol run under the same conditions except that the proton channel of the probe was detuned. It looks more like a DEPT-90 as the proton pulses are closer to 90 degrees than 135 degrees.
Remember to tune the proton channel!

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