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The first thing to do following the insertion of your sample in the magnet, is to set the temperature, as most chemical shifts are temperature dependent, including the lock signal. Use the command edte to open the temperature window in TopSpin. The current temperature is written in the center of the window (25.0 °C), and is labeled as corrected (Corr.) as it was previously calibrated using 99.8% deuterated methanol (CD₃OD).

The temperature set on the computer is slightly different from the actual temperature in the magnet.

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The lock is a separate NMR spectrometer within the spectrometer, which is specific to deuterium. In order to produce a high resolution NMR spectrum of a sample, it is key to keep a constant magnetic field strength over the duration of the experiment. This is achieved by "locking" the spectrometer to the frequency of deuterium, ie by centering the deuterium signal to a predefined frequency. This signal is constantly monitored and compensations for the external magnetic field (B₀) drift are made in order to keep the resonance frequency constant.

Modern NMR magnets do not drift much beyond 4 to 5 Hz per hour. Yet, this would be sufficient to lose spectral resolution (eg J-coupling) over a 1-hour experiment. As a reference, below are the current (as of February 2020) magnet drifts for our NMR spectrometers.

Tune and match

Shim

Data acquisition

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