8. 超音波照射によるルミノール発光のpH依存性について

概要

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The fluorescence spectra of 0.1 mM-luminol were measured in various pH's solutions by a fluorescence photometer The fluorescence emission peak was found at 450 nm and the excited peak was at 391 nm in lower pH's (pH < 6.5) solutions. The emission spectra were broadening and were red-shifted in the higher pH's (pH > 6.5) solutions although the excited spectra were not large changes. The fluorescence intensities were large changes dependent on the pH values of the solutions. It was found that the pKa_1^* value was 6.5 and the pKa_2^* value was estimated as 10.4 from the pH-dependent curves of the luminol (dibasic acid). The multibubble sonoluminescence from aqueous solutions containing luminol were observed in different pH's (pH =1.3 and pH = 10.6) solutions. Although there were no large changes of the spectra of different ultrasound frequencies (100 - 150 kHz) at 300 mV^<p-p>, the luminescence intensities at 141 kHz were changed in pH 1.3 or pH 10.6 solutions. The intensity in pH 10.6 solution was 215 times larger than that in pH 1.3 solution. It was considered that the intermediated state was mono-ionic form of diazo-quinone in pH's >10.4 (pKa_2^*) solutions. Furthermore, it was estimated the neutral form of luminol in lower pH's (< 6.5 = pKa_1^*) solutions. It was found the active ionic form of luminol sonoluminescence from the fluorescence pH-dependent curves (1.3 < pH < 10.6).
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