Fluorescence quenching scans

Note In the case of HPTLC plates the detection limit for the visual recognition of the violet = 530 nm) colored chromatogram zones was 20 ng per chromatogram zone. With the exception of the two tetrahydrosteroids the cor-ticosteriods could be detected on TLC plates with fluorescent indicators by reason of fluorescence quenching (Fig. 1 A). Figure 2 illustrates the absorption scans of the separations illustrated in Figures 1A and 1B. 

Xexc = 436 nm and X > 560 nm (cut off filter FI 56 (D)). Under the conditions used for scans B and C some substances appear as double peaks on account of fluorescence quenching at the center of the chromatogram zones as a consequence of the substance concentration being too high. 

The extent of fluorescence quenching often depends on the sorbent medium and is generally more severe for silica gel than for chemically bonded sorbents [183]. In many cases the emission signal can be enhanced by application of a viscous liquid to the layer before scanning the plate. Common fluorescence enhancing... 

The location of a compound within a lipid bilayer can be studied using X-ray diffraction [167], neutron diffraction [164], fluorescence quenching techniques [163], differential scanning microcalorimetry [164], or NMR techniques [168,169],... 

Figure 5. Thin-layer chromatogram of tris (2,3-dibromopropyl)phosphate on fluorescein impregnated silica gel solvent methylene chloride. Scan in fluorescence quench mom. (a) 3.7 /ig TRIS (b) 0.44 ttg TRIS.

The Zeiss PMQ 3 chromatogram analyzer is probably the most versatile thin-film scanner available (Fig.3.13). The system can be used for reflectance, transmission, simultaneous reflectance and transmission and fluorescence quenching. It has two direct fluorescence modes, one with filter emission and surface illumination at a direction of 90° to the surface of the plate, and the other with 45° illumination and monochromatic emission. The instrument can be used for scanning thin-layer chromatograms, paper... 

Quantification. Fluorescence quenched zones of samples and standards scanned at 276 nm. 

Fluorescence Quenching of Soil Fulvic Acid Emission Scans... 

Figure 1. Fluorescence quenching of emission spectra due to Cu(II) ion titration of 15 ppm soil fulvic acid at 0.1 M ionic strength and pH 5. The FA sample was excited at 335 nm and emission wavelengths were scanned from 300 to 600 nm. Cu(n) concentrations of each emission spectra are (a) 0 uM, (b) 4.9 uM, (c) 9.8 uM, (d) 14.7 uM, and (e) 22 uM.

---