Page 424 - Tandem Techniques

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Consequently, the important dispersion characteristics are not those that take place in the column, but,
as has already been discussed in some detail, those that occurs in the interface between the
chromatograph and the spectrometer and in the spectrometer itself. These two sources of dispersion, can
not only reduce element sensitivity, but also destroy the separation originally achieved in the column.
The magnitude of the extra column dispersion is particularly important if high-speed columns, packed
with very small particles, are being used since such columns produce very narrow peaks a few
microliters in volume. High-speed columns seem ideally suited for use with flame AAS instruments as
they can be operated at the flow rates necessary for efficient solvent aspiration into the spectrometer
nebulizer. Unfortunately, due to the basic design of most AAS instruments, a significant length of
tubing is necessary in the interface if normal operation of the spectrometer is not to be impeded. Katz
and Scott [4], solved this problem by the use of low dispersion serpentine tubing as the interface
between the exit from the UV detector of the liquid chromatograph, and the spectrometer. A diagram of
their interface is shown in Figure 10.1.

Figure 10.1
The LC/Flame AAS Serpentine Tubing Interface

The principle of low-dispersion tubing has already been discussed, and it is sufficient to say that the
outer interface tube was 49 cm long, 0.25 cm I.D. and merely protected the serpentine tube contained
inside. The inner serpentine tube had a peak-to-peak amplitude of 1 mm. An example of the