Fluorescence normal

The results of the gravimetric measurements of the hybridization are presented in Table 10. As in the case of fluorescence, normal hybridization results in a frequency shift that is much higher with respect to the unspecific and cold hybridization. Nonspecific hy-... 

Quenching can actually be used to create analytical methods. An example is that of fluorescent antibody assay. Here, a fluor is bound to an antibody but the binding constant is less than that for the antibody-antigen pair for which the antibody was generated. Binding quenches the fluorescence of the fluor. When a solution containing the native antigen is mixed with the fluor complex, the fluor is released and can fluoresce normally. There are numerous examples of this approach. 

Fluorescence quenching is described in terms of two mechanisms that show different dependencies on quencher concentration. In dynamic quenching, the quencher can diffuse at least a few nanometers on the time scale of the excited state lifetime (nanoseconds). In static quenching, mass diffusion is suppressed. Only those dye molecules which are accidentally close to a quencher will be affected. Those far from a quencher will fluoresce normally, unaware of the presence of quenchers in the system. These processes are described below for the specific case of PMMA-Phe quenched by MEK. 

The excitation spectrum of a fluorescent material, i.e., the incident radiation spectrum required for the induction of fluorescence, is determined by the absorption spectrum of the fluorescent material, which it often closely resembles, and by the efficiency with which the absorbed energy is transformed into fluorescence. Normally, the excitation spectrum is of higher photon energy (shorter wavelength) than that of the corresponding fluorescence emission, and in sensor schemes this has an effect in the choice of preferred fluorescent agent, compatible with appropriate optical detection devices. 

Why do siloxene and its derivatives exhibit fluorescence in contrast to all other colored compounds encountered in silicon chemistry So far, no investigations have been reported, but we can make some plausible conjectures. Fluorescence normally occurs if the absorbed radiant energy is not destroyed in a non-radiative process such as occurs in isolated centers of a molecule, in a lattice, or in a very rigid arrangement. 

Fluorescein retention measurements are converted to relative amount of fluorescence normalized against protein concentration. Test chemical exposure causing disruption of tight junctions will allow fluorescein molecules to penetrate the comeal tissue and become trapped within its epithelial layer. Thus, fluorescein molecules are used as a permeability tracer and applied in defining comeal epithelial and endothelial permeability (Watsky et al. 1989). FITC-retention provides a quantitative assessment for paracellular leakage... 

Fluorescence Normally refers to the visible light given out when a specimen is held in X-ray, UV or some visible light (e.g. sunlight). 

Figure 13.8. Raman spectra of R6G adsorbed from a methanol solution onto glassy carbon (B). The fluorescence normally encountered with 514.5 nm excitation is quenched upon adsorption to the conducting surface. Spectra of (A) solid R6G and (C) clean glassy carbon are shown for comparison. (Adapted from References 10 and 25 with permission.)...

One possible explanation of the data presented here is that fluorescence normally observed in the absence of aluminum is quenched as AF" complexes are formed. Simultaneously a new fluorescence peak for the complex may appear at slightly shifted wavelengths. The complex may have a higher quantum efficiency and therefore show greatly enhanced fluorescence. This hypothesis may be useful in... 

Fig. 46. Emission spectrum of bioluminescence (O), measured directly from the cuvette during warming of intermediate II in the presence of aldehyde, plotted togather with the fluorescence emission spectrum (A) of the phototransformed intermediate II. Ordinate intensity of bioluminescence and fluorescence normalized at the peak. From Balny and Hastings (1975). Reprinted with permission of Biochemistry. Copyright by the American Chemical Society.

Figure 4. (a) Malignant melanoma (Level III, 1.5 mm) on the back, (b) FDAP Except for some follicular-bound fluorescences (normal) there is no tumor-specific fluorescence. 

All the dextrins exhibited both normal and TICT fluorescence. Normal fluorescence was more intense in a- and y-functionalized CD in / -function-alized CD, the TICT emission prevailed. The position of the TICT fluorescence maximum in / -CD (500 nm) is 45 nm blue shifted with respect to that of a- and y-substituted dextrins [222,223]. These data indicate a... 

HGURE 2. Absorption spectrum of CfL aurantiacus at 4 K. The band at 873 nm is due to BChl a 866. The chlorosomal BChl a and BChl a 808 contribute about equally to the band at 801 nm. Dotted line excitation spectrum of BChl a 866 fluorescence, normalized at 872 nm (10). 

Filtered-Particle Inspection. Solids containing extensive inteiconnected porosity, eg, sintered metallic or fired ceramic bodies formed of particles that ate typically of 0.15-mm (100-mesh) screen size, are not inspectable by normal Hquid penetrant methods. The preferred test medium consists of a suspension of dyed soHd particles, which may be contained in a Hquid vehicle dyed with a different color. Test indications can form wherever suspensions can enter cracks and other discontinuities open to the surface and be absorbed in porous material along interior crack walls. The soHd particles that form test indications ate removed by filtration along the line of the crack at the surface where they form color or fluorescent indications visible under near-ultraviolet light (1,3). 

Fluorescent ultraviolet lamps within an apparatus that allows condensation cycles rather than the water spray typical of xenon arc tests have been developed for plastics testing (279). The spectral cutoff wavelength of the lamps used in the apparatus determines the severity of the test. Ultraviolet B (UVB) 313 lamps allow a significant irradiance component below 290 nm, which is normally filtered out by the earth s atmosphere. Ultraviolet A (UVA)... 

For an analyte of molecular weight 5000 and good chromatographic conditions, most photometric detectors can be expected to provide detection limits of 2—5 ng. Improvement into the mid-picogram or lower range normally requires the use of more sensitive detection means such as fluorescence or electrochemical detectors. 

Numerous high pressure Hquid chromatographic techniques have been reported for specific sample forms vegetable oHs (55,56), animal feeds (57,58), seta (59,60), plasma (61,62), foods (63,64), and tissues (63). Some of the methods requite a saponification step to remove fats, to release tocopherols from ceHs, and/or to free tocopherols from their esters. AH requite an extraction step to remove the tocopherols from the sample matrix. The methods include both normal and reverse-phase hplc with either uv absorbance or fluorescence detection. AppHcation of supercritical fluid (qv) chromatography has been reported for analysis of tocopherols in marine oHs (65). 

Table 1 Hsts several of the chemical deterrninations and the corresponding reactions uti1i2ed, which are available on automated clinical analy2ers. With the exception of assays for various electrolytes, eg, Na", K", Cl , and CO2, deterrnination is normally done by photometric means at wavelengths in the ultraviolet and visible regions. Other means of assay include fluorescence, radioisotopic assay, electrochemistry, etc. However, such detection methods are normally required only for the more difficult assays, particularly those of semm or urine constituents at concentrations below )Tg/L. These latter assays are discussed more fully in the Hterature (3,4).

To measure a residence-time distribution, a pulse of tagged feed is inserted into a continuous mill and the effluent is sampled on a schedule. If it is a dry miU, a soluble tracer such as salt or dye may be used and the samples analyzed conductimetricaUy or colorimetricaUy. If it is a wet mill, the tracer must be a solid of similar density to the ore. Materials hke copper concentrate, chrome brick, or barites have been used as tracers and analyzed by X-ray fluorescence. To plot results in log-normal coordinates, the concentration data must first be normalized from the form of Fig. 20-15 to the form of cumulative percent discharged, as in Fig. 20-16. For this, one must either know the total amount of pulse fed or determine it by a simple numerical integration... 

The X-ray determination of REE in geological samples is normally complicated by the relatively low concentrations of the REE, their complex X-ray spectra, the high concentration of matrix elements and the lack of reference standards with certified values for REE. A rapid and sensitive ion exchange and X-ray fluorescence procedure for the determination of trace quantities of rare earths is described. The REE in two U.S.G.S. standards, two inhouse synthetic mixtures and three new Japanese standards have been determined and corrections for inter-rare earth element interferences are made. 

In X-Ray Fluorescence (XRF), an X-ray beam is used to irradiate a specimen, and the emitted fluorescent X rays are analyzed with a crystal spectrometer and scintillation or proportional counter. The fluorescent radiation normally is diffracted by a crystal at different angles to separate the X-ray wavelengths and therefore to identify the elements concentrations are determined from the peak intensities. For thin films XRF intensity-composition-thickness equations derived from first principles are used for the precision determination of composition and thickness. This can be done also for each individual layer of multiple-layer films. 

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