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90-Degree Pulse Width Calibration

(A PDF version of this handout is available from the Handouts page or by clicking Here)

Many NMR experiments rely on 90 degree proton pulses for optimal performance (e.g. HSQC, NOESY). The default values that are determined by the facility may not be optimal for your sample because of differences in solvent, salt concentration, etc. Therefore, you will need to determine its value when you want to maximize the performance of certain experiments. This page will guide you through the procedure for calibrating a 90 degree pulse. Typically, you will look for the 360 pulse, which is a null spectrum, and then divide that value by 4 to get the 90.

picture of a 90degree pulse width dcalibration experiment

Figure 1. Example of a pulse width calibration experiment. The pulse width was arrayed from 2 microsecs to 40 microsecs in steps of 2. Positive maxima occur at 90 and 450 degrees. The spectra with almost no signal are the 180 and 360 degree pulse spectra. The 360-degree spectrum would be used to calculate the 90-degree pulse width.


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