A description of the experiments with PAHs will serve to illustrate the technique of CD-RTP, and provide a basis for assessing its advantages.
Each PAH analyte was dissolved in either methanol or acetone, after which the solvent was gently evaporated. Addition of a 0.10.5-mL aliquot of 1,2-dibromoethane (DBE) was followed by dilution with 0.01-M aqueous CD solution. Upon vigorous shaking, the complex was formed. The cloudy solution obtained was then deoxygenated for fifteen minutes with nitrogen gas prepurified in an Alltech Oxy-Trap.
All spectra were taken on a SPEX FLUOROLOG spectrophotometer with double excitation and emission monochromators. A 450-W xenon CW lamp was used as the excitation source, and a cooled R928 photomultiplier (PMT) tube as the detector. Slits were set to 14.4 nm (excitation) and 3.6 nm (emission). The scan rate was 1 nm s1. All emission spectra were corrected for fluctuations in the intensity of the lamp and PMT responses.
Results and Discussion
The investigation showed the CD-RTP technique to be extremely sensitive, producing intense, well-structured phosphorescence signals at nanomolar concentrations. Detection limits of two typical phosphors, phenanthrene and acenaphthene, were estimated at 5 1013 M and 1 1011 M, respectively. Although the excited triplet state is known to be susceptible to oxygen quenchers, inclusion of the lumiphor inside the CD cavity was observed to offer some protection against quenching by oxygen molecules in the bulk solution. In these experiments, 10