Fluorescence and Scattering

Matrix absorption, secondary fluorescence and scattering phenomena limit sensitivity and precision in many cases, especially with dense matrices. The sensitivity falls off with atomic number elements with Z < 15 are particularly difficult to analyse. Analysis is characteristic of surface layers (5-500 pm depth) only for a solid specimen. Instruments are often large, complicated and costly. 

In addition to absorption problems, measurements will be affected by secondary fluorescence and scattered radiations which will enter the detector and increase the general background. Detection limits under optimum conditions (a heavy element in a light matrix) may be as low as 10 ppm. Quantitative analysis is however difficult below the 20-100 ppm region if a reasonable precision (5% or better) is to be obtained. 

Schrader, B., Micro Raman, Fluorescence, and Scattering Spectroscopy of Single Particles, in Physical and Chemical Characterization of Individual Airborne Particles (K. R. Spurny, Ed.), Chap. 19, pp. 358-379, Ellis Horwood, Chichester, 1986. 

A. excitation could greatly reduce photolytic interference, nonresonant fluorescence, and scattering backgrounds. The method can be calibrated by fundamental calculation or by ozone photolysis by a shortwave UV source. The successful 2-A determination of NO provides confidence in the fundamental principles of this technique and shows its adaptability for nonsimul-taneous measurements of NO, N02, and HN03. 

The recent interest in light absorption, fluorescence, and scattering... 

Fiber-optic probes can provide data on absorbance, diffuse reflectance, fluorescence, and scattering. (Courtesy of Guided Wave, Inc.)... 

A glycogen solution placed in the emission compartment will scatter fight and is used as reference (rrf = 0) to determine the phase delay and fluorescence demodulation. For each measurement, the reference intensity is adjusted so that it is equivalent to the intensity of the fluorescence signal of the sample. Phases and modulations of the fluorescence and scattered fight are obtained relative to the reference photomultiplier or instrumental... 

X-Ray methods are used for qualitative and quantitative elemental analysis, and for determination of crystal and molecular structure, by measurement of the absorption, emission, fluorescence, and scattering of... 

The conformation of natural organic molecules under various solution conditions is of particular interest in water treatment, as the structure of the molecules may influence their packing and water permeability. The fractal dimension reflects the space occupied by the disordered system. Senesi et al. described a method using a UV/VIS spectrophotometer to measure the fractal dimension of humic aggregates (Senesi (1994), Senesi et al (1994,1996,1997)). At low pH the a egates were of a compact, collapsed, less porous structure, whereas at a higher pH they were more expanded, open, and of fluffy structure. While the method appeared to work well for the published data, the simultaneous variation of absorbance, fluorescence, and scattering casts some doubt on the method. 

We have made EXAFS measurements on the SI state of PS2 particles at the SERC Daresbury laboratory, using a slitless monochromator and 13-element solid state Si-Li detector that gives improved resolution of fluorescent and scattered signals. 

In a nonresonance fluorescence transition, the photons involved in absorption and fluorescence processes have different wavelengths (Figure IB). The particular transition shown in Figure IB is called Stokes direct-line fluorescence, which is frequently used for AFS with laser excitation. Nonresonance transitions have the advantage that a wavelength selection device can be used to distinguish between fluorescence and scattered source radiation. 

To measure SPP in the absence of fluorescence and scattered radiation, it is necessary to use a phosphor-oscope or a pulse-source gated detector. A phosphoro-scope is a mechanical device, at present not used, that... 

A. M. Winkler et ah. Fluorescent and scattering contrast agents in a mouse model of colorectal cancer. Proceedings of the SPIE, 6851, 68510L (2008). 

FIGURE 2.4 Fluorescence and scattering efficiency in NIR- and VIS-Raman spectroscopy. 

M. 1. Kaniu, K. H. Angeyo, A. K. Mwala and F. K. Mwangi, Energy dispersive X-ray fluorescence and scattering assessment of soil quality via partial least squares and artificial neural networks analytical modeling approaches, Talanta, 2012, 98, 236-240. 

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