Page 456 - Tandem Techniques
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displaced into the NMR cell for NMR examination. This latter technique also allows all the normal
techniques of high-resolution NMR to be used.
The Basic LC/NMR Tandem System
A diagram of a modern LC/NMR tandem system is shown in Figure 11.2. For the most part, modern
LC/NMR systems are not really used as in-line devices, but more often function as automatic fraction
collectors that pass the sample to the NMR spectrometer for examination by a normal static, or stop-
flow, procedure. They are unique in that the cell is designed for a flow-through function and, as a
consequence, must have a small sample volume.
Figure 11.2
The Layout of Modern LC/NMR Tandem System
Courtesy of Varian Instruments Inc.
They also have special valving arrangements, some of which can be quite complex, to direct the column
and solvent flows appropriately for fraction collection and sample monitoring. Nevertheless, as already
stated, the spectra are generally run on a stop-flow principle; the sample being held in the cell while the
spectra are obtained. This is often a direct result of
