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phosphate. The structural analog, 2-(2-methoxy-4-biphenyl)propionic acid was used as an internal
standard. 100 µl aliquots of the supernatant liquid were separated on a Waters µBondepak C18 column,
using a mixture of 55% of 0.05M potassium phosphate (pH 2.6), and 45% tetrahydrofuran as the mobile
phase. The optimum excitation wavelength was 260 nm and the emission wavelength that was
monitored was 320 nm. An excellent separation was obtained and as a result of the selectivity of the
spectrometer when operated at the optimum excitation wavelength, and monitoring at the optimum
emission wavelength of the substances of interest, the peaks were completely free from undetected
contaminant materials. The recoveries of the drug and metabolite ranged from 97.4% to 105.5%. The
lower limit of detection for the drug, Flurbiprofen, was approximately 1 x 10-6 g/ml, with a linear
dynamic range extending to 50 x 10-6 g/ml. The linear range is small, but no less than would be
expected for fluorescence measurements.

The same type of apparatus was used by Soroka et al. [3] to determine a number of different metals as
their fluorescent 8-hydroxyquinoline-5sulfonic acid complexes. Nearly 80 different metal species were
examined and the optimum excitation wavelengths and emission wavelengths for each were reported.
Some examples of which are given in Table 7.3

Table 7.3 Optimum Excitation Wavelengths and Optimum Emission Wavelengths of the 8-
hydroxyquinoline-5-sulfonic acid Complexes Some Metal Elements
Metal l l, Optimum Excitation l l, Optimum Emission
(nm) (nm)
Zinc 393 506
Cadmium 387 522
Magnesium 393 506
Calcium 393 506

The 8-hydroxyquinoline-5-sulfonic acid chelating reagent must be carefully purified before use, to
eliminate any trace of fluorescing materials that would contribute background noise to the
measurements.