Fluorometric Characteristics of a Wave‐Guide Cell with Low Refractive Index

Abstract

Recently, Teflon AF2400 (AF 1600, and AF 1601) was commercialized (DuPont Fluoroproducts, Wilmington, DE, U.S.A), that has a refractive index (1.29) lower than water (1.33), and which means that the wave‐guiding of light is possible in water. In this study, we used Teflon AF 2400 as a waveguide capillary longpath cell for fluorometry. He‐Cd and Ar⁺ lasers were used as the excitation source, at 325 nm and 514.5 nm respectively. The length of the capillary wave‐guide cell was 18.70 cm. The was wound twice on a flat surface (loop diameters: 2 cm and 3 cm). The excitation was executed through the wave‐guide cell and the fluorescence from the wound capillary cell wall was collected in a perpendicular direction to the loop. With excitation at 325 nm, the fluorescence intensity at 450 nm emitted from the cell wall decreased along with the increase in the refractive index of the solvent. This can be caused by attenuation of the source light due to absorption by the solvent. In our experiment, the solvent of higher refractive index has the higher absorption at 325 nm. On the other hand, the fluorescence intensity at 590 nm, with excitation at 514.5 nm, increases with increased refractive index of the solvent. This result shows that an increase in the refractive index of the solvent is preferable for maintaining the wave‐guiding of the source light. Here, the characteristics of fluorescence spectrometry are discussed in terms of the collection of fluorescence from the wave‐guide capillary cell wall.

Keywords:

• Fluorometry
• Water‐core wave guide
• Teflon capillary of low refractive index
• Solvents

Acknowledgments

We would like to thank Mr. Chikaro Kojima for his help to make the figures in this paper. This research was supported by Grant in Aid (# 14340235) for Scientific Research (B) from the Ministry of Education, Culture, Sports, Science and Technology, and Grant for private universities provided by Ministry of Education, Culture, Sports, Science and Technology and The Promotion and Mutual Aid Corporation for Private Schools of Japan.