Page 271 - Tandem Techniques
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Chapter 7
Liquid Chromatography/Uv Spectroscopy Fluorescence Spectroscopy (LC/UV/FS)
Tandem Systems
LC/UV Tandem Systems
Today, the liquid chromatograph/UV spectrometer combination is hardly recognized as a tandem
instrument, as it is in such common use. The UV diode array spectrometer is one of the most commonly
used LC/UV instruments and consequently, the system is regarded more as a multi-wavelength detector
than as a tandem instrument. In fact, its use as a device to produce UV spectra is relatively limited
compared with its use to select the optimum wavelength for maximum light absorption, and
consequently allow the separation to be monitored at the maximum sensitivity. The limitations of UV
spectra for confirming solute identity have already been discussed in Chapter 2. Certain compounds,
such as those containing aromatic rings, give spectra with sufficient fine structure to aid in solute
identification. Unfortunately, the spectra of the majority of substances are very similar in shape, have
little or no fine structure, and are therefore virtually useless for this purpose.
In addition, the resolution obtainable from the diode array spectrometer is limited by the number of
diodes in the array, and consequently unless a large number of diodes are employed, the limited
resolution could impair the certainty of identification. This limitation will be particularly pertinent when
fine structure is present in the spectrum.
