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also provide the necessary high NMR sensitivity. The cell had a sensor volume of 60 µl, which is far
too large for microbore columns, but can be used successfully with wider bore columns. The spectra
were obtained by stopping the column flow when the peaks were in the sensor cell, and running the
spectra in the normal way. Using this technique, it is clear that a multiple peak can be scanned (a form
of peak slicing). It is seen from the insert chromatogram obtained from the UV detector that there are
two unresolved solutes present in the peak, and the NMR spectra taken across the peak clearly differ as
shown in Figure 11.5.

Even though the components are not resolved, a shoulder on the main component peak yields an
identifiable spectrum that is quite different from that taken from the front portion of the peak. The areas
of the NMR spectra that demonstrate the change that results during the final elution of the first peak,
and the start of the elution of the second peak, are depicted by arrows. This type of tandem system can
provide unambiguous confirmation of solute identity that is ideal for forensic purposes.

Capillary LC-NMR Coupling: High Resolution 1H NMR Spectroscopy in the Nanoliter Scale

Although coupling the liquid chromatograph with the NMR spectrometer produces one of the most
powerful analytical systems available, it has done so in the past at a price. If the tandem combination is
to be employed with the modern miniaturized LC systems, then the detection, or sensing volume, must
be greatly reduced, and this reduction is usually accompanied by a dramatic loss in NMR resolution.

In general there are two types of sensing coils used in NMR probes, the 'saddle' coil and the 'solenoid'
coil. These two types of coil take the form depicted in Figure 11.6A. There are also two basic types of
flow cell that are used in LC/NMR and these are depicted in Figure 10.6B. The choice of coil is largely
determined by the choice of flow cell. However, modern chromatographic systems are tending to
smaller and smaller bore columns and thus the cell volume is required to be as small as possible. As a
consequence the flow cell show on the right of Figure 11.6B used in