The Effect of the 2H Lock on Environmental Instability

The ²H lock of an NMR spectrometer continuously monitors the frequency of the ²H resonance of a deuterated solvent used to prepare the NMR sample.  If the frequency of the ²H resonance changes due to an environmental instability while the lock is engaged, a feedback mechanism is used to correct the magnetic field via a B_o shim coil, returning the ²H resonance to its original position.  It is very effective at reducing (if not eliminating) environmental instability from NMR data collected over periods of time spanning minutes or hours.  The effect of the lock is illustrated in the figure below.

Each panel in the figure represents a contour plot of a pseudo 2D ¹H NMR data set for the residual protons of D₂O on a Bruker Fourier 300 NMR spectrometer.  Each panel represents 2048 single-scan 1D ¹H NMR spectra collected over 1.5 hours.  The data in the left-hand panel were collected during the day without the ²H lock.  The data in the center panel were collected in the middle of the night without the ²H lock.  The data in the right-hand panel were collected during the day using the ²H lock.  The ²H lock clearly compensates for environmental instability.  There was no student traffic in the lab during the collection of any of the data.  Outside of the lab are two construction sites which are busiest during the day and quieter at night.  This is reflected in a comparison between the left-hand and center panels of the figure.  The data collected in the middle of the night without the ²H lock show somewhat less instability compared to similar data collected during the day.