Page 295 - Tandem Techniques

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The authors demonstrated the efficacy of their system by monitoring the chromatographic separation of
the zinc, cadmium, magnesium and calcium complexes by fluorescence detection using the optimum
excitation and emission wavelength given in Table 7.3. It is seen that for the metals examined, the
optimum excitation and emission wavelengths are very similar, and seems to be more a function of the
characteristics of the chelating agent than those of the metals. The sensitivity of the system indicated a
wide variation between metals, the minimum appearing to be about 5 x 10-12 mol.

The Multiwave Fluorescence Detector

Tanabe et al. [4] developed a novel instrument that employed interference filters in an attempt to
provide multiwave fluorescence detection without using a monochromator. The device operated at four
different wavelengths and a diagram of their apparatus is shown in Figure 7.18. The excitation light
from a 200 W xenon arc lamp was first reflected by a UV mirror (90% average reflectance for light
between 325 and 475 nm) to minimize heat transfer and remove most of the visible light. The excitation
light then passed through interference filters that could transmit light at 320 ± 2 nm, 360 ± 2 nm and
400 ± 2 nm, and was then focused onto the rounded shaped end of a quartz optical fiber bundle. This
fiber bundle directed the light to the detector module, which consisted of a square quartz tube mounted
in a black Teflon cell holder. The fluorescence signal was observed through side windows in the cell.
Two detector assemblies, each consisting of a light sensor and an interference filter, were mounted in
brass holders on either side of the cell. Consequently light emission at four different wavelengths could
be measured simultaneously. Different filters were used for different excitation light frequencies; for
example, with an excitation light wavelength of 400 nm, the filters in the four sensor units were chosen
to transmit light at 420 ± 2 nm, 440 ± 2 nm, 460 ± 2 nm and 500 ± 2 nm respectively. The output from
the sensors was acquired by a computer and the data stored. The separation, monitored by any one of
the fluorescence channels, could then be reconstructed. An example of the use of the apparatus to
resolve a convoluted peak containing two solutes is shown in Figure 7.19.