Deuterium lock channel

These types of experiments call for efficient doubly tuned coils, ideally with a separate deuterium lock channel. For more complex molecules, such as proteins, considerably more intricate NMR pulse sequences, such as (HNCO) [32,33], require the probe to operate at three or four distinct frequencies. High efficiency is demanded from the proton observe channel. Ideally, the additional circuitry allowing multiple tuning should not interfere with the proton efficiency when compared to a singly tuned proton coil. In practice, some reduction is tolerated. The two most important design criteria for such... 

The deuterium lock channel is the part of the NMR instrument that monitors the frequency of the H s in the sample and adjusts the strength of the applied field so that the frequency of whatever nuclide is being observed is known. The frequency of the NMR signal is monitored every 500 ns and applied field strength is adjusted to maintain a constant value. 

THE DEUTERIUM LOCK FEEDBACK LOOP 3.3.1 The Lock Channel... 

Lithium-6 edited C-spin-echo methods have been described and can be used with success in an investigation of aggregate formation of lithiumorganyls [12]. Since Li resonates close to deuterium, the experiments can in principle be performed in a standard multinuclear probehead by employing the lock channel as the third pulsed radiofrequency channel. 

The deuterium nucleus, used normally for the lock channel, can be employed as an internal NMR thermometer." Using two deuterated compounds, a power pseudo-FID can be constructed from either a conventional continuous wave (CW) deuterium sweep or a pulsed deuterium FID. The Fourier transform of this signal gives a Lorentzian line with double the natural... 

The lock channel regulates the field by monitoring the dispersion mode deuterium resonance rather than the absorption mode signal that is usually considered in NMR, and aims to maintain the centre of this resonance at a constant frequency (Fig. 3.45). A drift in the magnetic field alters the... 

Despite the impressive field stability provided by superconducting magnets, they still have a tendency to drift significantly over a period of hours, causing NMR resonances to drift in frequency leading to a loss of resolution. To overcome this problem, some measure of this drift is required so that corrections may be applied. On all modem spectrometers, the measurement is provided by monitoring the frequency of the deuterium resonance of the solvent. The deuterium signal is collected by a dedicated observe spectrometer within the instrument that operates in parallel with the principle channels, referred to as the lock channel or simply the lock. 

The ideal solvent should contain no protons and be inert, low boiling, and inexpensive. Deuterated solvents are necessary for modem instruments because they depend on a deuterium signal to lock or stabilize the B0 field of the magnet. Instruments have a deuterium channel that constantly monitors and adjusts (locks) the B ) field to the frequency of the deuterated solvent. Typically, H NMR signals are in the order of 0.1 to several Hz wide out of 300,000,000 Hz (for a 300 MHz system), so the B ) field needs to be very stable and homogeneous. 

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