Analyte fluorescence

Fluorimetric methods of analysis make use of the natural fluorescence of the analyte, the formation of a fluorescent derivative or the quenching of the fluorescence of a suitable compound by the analyte. Fluorescence cannot occur unless there is light absorption, so that all fluorescent molecules absorb, but the reverse is not true only a small fraction of all absorbing compounds exhibits fluorescence. The types of molecule most likely to show useful fluorescence are those with delocalised ji-orbital systems. Often, the more rigid the molecule the stronger the fluorescence intensity. Naturally fluorescent compounds include Vitamin A, E (tocopherol). 

Fluorescence detection, because of the limited number of molecules that fluoresce under specific excitation and emission wavelengths, is a reasonable alternative if the analyte fluoresces. Likewise, amperometric detection can provide greater selectivity and very good sensitivity if the analyte is readily electrochemically oxidized or reduced. Brunt (37) recently reviewed a wide variety of electrochemical detectors for HPLC. Bulk-property detectors (i.e., conductometric and capacitance detectors) and solute-property detectors (i.e., amperometric, coulo-metric, polarographic, and potentiometric detectors) were discussed. Many flow-cell designs were diagrammed, and commercial systems were discussed. 

The two SERS bands of eosin at 292 and 500 cm" are developed in spectrum 1 on Fig. 2b. It indicates the major plasmon-dependent mechanism of fluorescence enhancement. Besides the plasmon enhancement, the interference effect between two silver surfaces is possible. We suggest that both these effects are responsible for an observable phenomenon. But more sensitive parameters for the secondary emission enhancement can be tuned through engineering of LP band position and optical density. The low and disadvantageous spectral overlap of LP and molecular absorption bands, as well as the silver deposition excess lead to the significant quenching of analyte fluorescence. 

Nonluminescent impurities may also interfere by quenching analyte fluorescence. They may be removed much as luminescent impurities are removed. 

Hill HR, Martins TB. The flow cytometric analysis of cytokines using multi-analyte fluorescence microarray technology. Methods 2006 38 312-316. 

L. W. Burgess, M.-R. S. Fuh, and G. D. Christian, Use of Analytical Fluorescence with Fiber Optics, in P. Eastwood and L. J. Cline-Love, eds. Progress in Analytical Luminescence, ASTM STP 1009, Philadelphia American Society for Testing and Materials, 1988. 

Summary. Methods for determining the aqueous solubilities of PAHs are subject to errors associated with the preparation, extraction, and quantitative analysis of saturated solutions. There is no one method that has addressed the problems associated with each of these processes. Systematic errors associated with quantitative analyses of saturated solutions should be reduced in methods where selective analytical measurement techniques are used. Chromatographic methods allow separation of nonanalyte signals-in-time from those of the analyte. Fluorescence spectroscopy allows greater selectivity than UV spectroscopy, though less than gas or liquid chromatography. 

Laser Fluorescence Noise Sources. Finally, let us examine a technique with very complex noise characteristics, laser excited flame atomic fluorescence spectrometry (LEAFS). In this technique, not only are we dealing with a radiation source as well as an atomic vapor cell, as In atomic absorption, but the source Is pulsed with pulse widths of nanoseconds to microseconds, so that we must deal with very large Incident source photon fluxes which may result in optical saturation, and very small average signals from the atomic vapor cell at the detection limit [22]. Detection schemes involve gated amplifiers, which are synchronized to the laser pulse incident on the flame and which average the analyte fluorescence pulses [23]. 

See alsa Carbohydrates Overview Sugars - Chromatographic Methods. Derivatization of Analytes. Fluorescence Fluorescence Labeling. Liquid Chromatography Size-Exclusion. Spectrophotometry ... 

With external standardization, an equivalent analyte concentration in the standard and sample should yield the same analyte fluorescence signal. The accuracy of the determinations is dependent on interferences, chemical equilibrium involving the analyte, scattering, and quenching. Analyte interference due to absorption, scattering, or quenching may be... 

See also. Analytical Reagents Specification. Derivat-ization of Analytes. Fluorescence Derivatization Fluorescence Labeling Quantitative Anaiysis. Lipids Fatty Acids. Liquid Chromatography Liquid Chromatography-Mass Spectrometry Pharmaceuticai Applications. Mass Spectrometry Forensic Appiications. Spectrophotometry Derivative Techniques. 

See also Derivatization of Analytes. Fluorescence Derivatization. Liquid Chromatography Amino Acids. Pharmaceuticai Appiications. 

Spectral interferences can be significant in AFS and some of them are unique to AFS. The total fluorescence signal at the detector can include light scattered from the source, fluorescence from nonanalyte atoms and molecules, background emission, analyte emission, and analyte fluorescence. To measure only analyte fluorescence, the other spectral interferences must be eliminated or... 

Major Applications Sensors, measuring chemical analytes, fluorescence lifetime in cells," fluorescent pH detector system ... 

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