Reflectance fluorometry

The development of hydrodynamic techniques which allow the direct measurement of interfacial fluxes and interfacial concentrations is likely to be a key trend of future work in this area. Suitable detectors for local interfacial or near-interfacial measurements include spectroscopic probes, such as total internal reflection fluorometry [88-90], surface second-harmonic generation [91], probe beam deflection [92], and spatially resolved UV-visible absorption spectroscopy [93]. Additionally, building on the ideas in MEMED, submicrometer or nanometer scale electrodes may prove to be relatively noninvasive probes of interfacial concentrations in other hydrodynamic systems. The construction and application of electrodes of this size is now becoming more widespread and general [94-96]. 

By the total internal reflection condition at the liquid-liquid interface, one can observe interfacial reaction in the evanescent layer, a very thin layer of a ca. 100 nm thickness. Fluorometry is an effective method for a sensitive detection of interfacial species and their dynamics [10]. Time-resolved laser spectrofluorometry is a powerful tool for the elucidation of rapid dynamic phenomena at the interface [11]. Time-resolved total reflection fluorometry can be used for the evaluation of rotational relaxation time and the viscosity of the interface [12]. Laser excitation can produce excited states of adsorbed compound. Thus, the triplet-triplet absorption of interfacial species was observed at the interface [13]. 

In the mechanism of an interfacial catalysis, the structure and reactivity of the interfacial complex is very important, as well as those of the ligand itself. Recently, a powerful technique to measure the dynamic property of the interfacial complex was developed time resolved total reflection fluorometry. This technique was applied for the detection of the interfacial complex of Eu(lII), which was formed at the evanescent region of the interface when bathophenanthroline sulfate (bps) was added to the Eu(lII) with 2-thenoyl-trifuluoroacetone (Htta) extraction system [11]. The experimental observation of the double component luminescence decay profile showed the presence of dinuclear complex at the interface as illustrated in Scheme 5. The lifetime (31 /as) of the dinuclear complex was much shorter than the lifetime (98 /as) for an aqua-Eu(III) ion which has nine co-ordinating water molecules, because of a charge transfer deactivation. 

Recently, the formation of the dinuclear Eu(II) complex at the toluene-water interface was found out by a time-resolved total reflection fluorometry. When bathophenanthroline sulfate (bps) was added to the extraction system of Eu(III) with 2-thenoyltrifluoroacetone (Htta), a double component luminescence decay profile was observed and it showed the presence of dinuclear complex at the interface [27]. The observed life times x — 22 and 203 ps were attributed to the dinuclear complex Eu2(tta)2(bps)2 and the mononuclear complex Eu(tta)2bps. The shorter lifetime of the dinuclear complex than x = 98 ps for an aqua-Eu(III) ion suggested a charge transfer deactivation in the dinuclear complex. 

M. Fujiwara, S. Tsukahara, and H. Watarai, Time-resolved total internal reflection fluorometry of ternary europium(III) complexes formed at the liquid-liquid interface, Phys. Chem. Chem. Phys., 1, 2949-2951 (1999). 

Alumina (Chromarods A) was as good as silica gel (Chromarods S 111) for the separation of neutral lipids, but silica gel produced better separation and higher FID response for polar lipids Chromarods S-III (silica gel-coated quartz rods) were used to quantify neutral and polar lipids in cooked beef Nile red solution used for detection of lipids densitometry by reflectance fluorometry detection limit of assay was 25-100 ng for each lipid... 

Ishizaka, S., H. B. Kim, and N. Kitamura, Time-resolved total internal reflection fluorometry study on polarity at a Uquid/Uquid interface. Anal Chem, Vol. 73, (2001) p. 2421. 

---