Page 59 - Tandem Techniques

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a fiber optical system. Alternatively the section of tube is irradiated by an appropriate laser, and the
intensity of the fluorescent light monitored with an appropriate light-sensing cell. The sample is
introduced into the system using electro-osmotic flow by connecting a high potential to the electrode in
the sample reservoir. When sufficient sample has passed into the tube, the high potential is again
connected to the anode in the anode reservoir and the separation developed. Whereas tandem systems
using GC and LC as the basic separation techniques are now commonplace, this is not so for tandem
systems based on capillary electrophoretic separations. However, as already suggested, this may well
change in the near future.

Synopsis

Early analytical procedures were carried out sequentially, not concurrently, and consequently were very
time consuming. Analytical instruments were first introduced in the late 1940s and started to become
established in the 1950s. The first instruments to be introduced were UV and visible spectrometers
followed by the gas chromatograph and IR spectrometer. The development of sophisticated analytical
instruments opened up the possibility of combining a separation technique with an identification
technique and thus permit concurrent analyses. There are two basic separation techniques employed
with tandem systems, GC and LC; these techniques can be sub-divided, depending on the nature of the
stationary phase, to GLC, GSC, LLC, and LSC. A gas chromatograph consists of a gas supply, gas
controllers, injector, column oven and detector. The three most common detectors are the FID, the
katherometer and the electron capture detector. There are two types of column employed in the gas
chromatograph, the packed column and the capillary column. The former provides higher loading
capacities, larger peak volumes but lower resolution, the latter has a very low loading capacity, very
small peak volumes but can provide very high resolution. The packed column requires a simple septum
injector for sampling whereas the capillary column needs more involved systems such as the split
injector. The basic liquid chromatograph consists of a solvent programmer, pump, injection valve,
column and column oven, and a detector. Packed columns are almost exclusively employed in LC,
although some have very small