Environmentally shifted fluorescence lifetimes for multicomponent phase-modulation fluorimetric analysis

Several cyclodextrins, surfactants, and a series of three organic solvents-methanol, isoamylic alcohol, and hexanol-with different polarities and viscosities, were used to study the influence of the microenvironment on the fluorescent behavior of three diuretics-furosemide, triamterene, and piretanide. We concluded that on going from methanol to hexanol, the fluorescence lifetime of furosemide from 0.91 to 2.10 ns, that of triamterene from 4.54 to 4.44 ns, and that of piretanide from 5.24 to 10.37 ns. At 40 MHz, the phase shifts (excitation/emission) produced by furosemide, triamterene, and piretanide were 12.0, 29.6, and 30.2° in methanol and 27.8, 48.1, and 69.0° in hexanol. A three-factor, three-level factorial design allowed us to establish a calibration matrix of the three diuretics that covered the three ranges from 10 to 40, 1.5 to 6, and 0.1 to 0.4 μM for furosemide, piretanide, and triamterene, respectively. Data processing incorporated PLS adjustment values. The function was fitted to a phase-resolved fluorescence intensity at the three phase angles selected. Percentages recoveries were from 88 to 115%.