Page 459 - Tandem Techniques
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chosen that will provide the required resolution. Subsequently, the sample can be expelled from the cell,
with solvent supplied directly from the chromatography pump. The third alternative is to direct the
eluent from the column to a sample loop where it can be stored until the spectrometer is available to
take data. This is basically a fraction collecting system. If necessary, a number of solutes can be stored
in different loops and they can be examined when convenient. When the data has been acquired from
one sample, the solute stored in the next loop can then be displaced into the NMR cell and examined.
Samples that have been examined can either be displaced to waste or collected for further examination.
A photograph of the Varian flow control device for their LC/NMR tandem instrument is shown in
Figure 11.4.
An interesting example of the use of the Varian LC/NMR system in handling two unresolved peaks is
shown in Figure 11.5.
Figure 11.5
NMR Spectra Taken Across an Unresolved Peak Using
the Varian Interface System the LC/NMR System
Courtesy of Varian Inc.
The spectra were obtained using Varian's new LC-NMR Microflow probe, which was developed to
maintain good chromatographic resolution and
