Fluorescent technique

Riboflavin can be assayed by chemical, en2ymatic, and microbiological methods. The most commonly used chemical method is fluorometry, which involves the measurement of intense yeUow-green fluorescence with a maximum at 565 nm in neutral aqueous solutions. The fluorometric deterrninations of flavins can be carried out by measuring the intensity of either the natural fluorescence of flavins or the fluorescence of lumiflavin formed by the irradiation of flavin in alkaline solution (68). The later development of a laser—fluorescence technique has extended the limits of detection for riboflavin by two orders of magnitude (69,70). 

Mercury generally is found in low and trace concentrations. So there is need to determine Hg in ranges corresponding to various types of water samples. Detection levels of Hg can be improved by the use of vapour generation technique. This technique allows to sepai ate the analyte from the sample matrix and so to overcome the matrix interference. The fluorescence technique, with its high sensitivity and linearity, in combination with vapour generation, provides for a possibility to detect Hg in parts per trillion per liter regions. 

In general the limit of detection of the fluorescence technique is of the order of 103 times lower than that for UV absorption spectrometry. 

Ghiggino, K. P., Roberts, A. J. and Phillips, D. Time-Resolved Fluorescence Techniques in Polymer and Biopolymer Studies. Vol. 40, pp. 69— 167. 

George, L.A. Development of a Direct, Low Pressure, Laser-induced Fluorescence Technique for NO2, Ambient Measurements and Urban NO, Ph.D. Thesis, Portland State University Portland, OR, 1991,1-135. 

In current practice the fluorescence assay is often followed by the use of hybridization techniques when more selectivity is required. We have for instance used the fluorescence techniques to obtain data on the nucleic acid content of malaria vaccine proteins produced in Escherichia coli. The rapid turnaround time of the fluorescence assay is particularly useful during the early stages of purification to determine the optimal process conditions. After the final process has been arrived at and a variety of methods used to assess the nucleic acid content (including the hybridization techniques), the fluorescence method can be developed for routine quality-control purposes. In certain cases, particularly at high protein concentrations, the dye may bind to the protein with... 

Sawicki (13) used solid-surface fluorescence techniques extensively in the 1960 s for air pollution research. In 1967, Roth (14) reported the RTF of several pharmaceuticals adsorbed on filter paper. Schulman and Walling (15) showed that several organic compounds gave RTF when adsorbed on filter paper. Faynter et al. (16) reported the first detailed analytical data for RTF and gave limits of detection, linear dynamic ranges, and reproducibilities for the compounds. 

In this chapter, we present the theory and results of measurements on humic acid fractions using fluorescence techniques. The fluorescence techniques are attractive for this application because of the natural fluorescence of humic materials, the hi sensitivity of fluorescence detection, and the ability to directly observe the morphology of the molecule in aqueous solutions without the need for drying or applying harsh chemical conditions. Several interesting types of information are obtained from fluorescence measurements ... 

Zhang, L., "Experimental Research on the Properties of Si02-Hydrosol Flows with Fluorescence Technique, Beijing, Ph.D thesis, Tsinghua University, 2004. 

The PSP toxins represent a real challenge to the analytical chemist interested in developing a method for their detection. There are a great variety of closely related toxin structures (Figure 1) and the need exists to determine the level of each individually. They are totally non-volatile and lack any useful UV absorption. These characteristics coupled with the very low levels found in most samples (sub-ppm) eliminates most traditional chromatographic techniques such as GC and HPLC with UVA S detection. However, by the conversion of the toxins to fluorescent derivatives (J), the problem of detection of the toxins is solved. It has been found that the fluorescent technique is highly sensitive and specific for PSP toxins and many of the current analytical methods for the toxins utilize fluorescent detection. With the toxin detection problem solved, the development of a useful HPLC method was possible and somewhat straightforward. 

Detection of the PSP toxins has proven to be one of the largest hurdles in the development of analytical methods. The traditional means, and still in wide use today, is determination of mouse death times for a 1 mL injection of the test solution. There are a variety of drawbacks to utilization of this technique in routine analytical methods, that have prompted the search for replacements. In 1975 Bates and Rapoport (3) reported the development of a fluorescence technique that has proven to be highly selective for the PSP toxins, and very sensitive for many of them. This detection technique has formed the basis for analytical methods involving TLC (77), electrophoresis (72), column chromatography (7J), autoanalyzers (7 ), and HPLC (5,6,7). 

Structure and Dynamics of a Confined Polymer Chain Studied by Spatially and Temporally Resolved Fluorescence Techniques... 

A fully automated instrumental procedure has been developed for analyzing residual corrosion inhibitors in production waters in the field. The method uses ultraviolet (UV) and fluorescence spectrophotometric techniques to characterize different types of corrosion inhibitors. Laboratory evaluations showed that fluorescence is more suitable for field application because errors from high salinity, contamination, and matrix effect are minimized in fluorescence analysis. Comparison of the automated fluorescence technique with the classic extraction-dye transfer technique showed definite advantages of the former with respect to ease, speed, accuracy, and precision [1658],... 

By their nature, many UV absorbers are amenable to analysis by fluorimetric analysis. In many instances visible fluorescence techniques are less subject to interference by other polymer additives in a polymer extract than are UV methods of analysis. In fluorescence analysis (ex at 367 nm, em at 400-440 nm) of a PS/Uvitex OB chloroform dissolution AOs such as Ionol CP, Ionox 330, Polygard and Wingstay T/W do not interfere detection limit of 10 ppm [41]. 

M.W. Urban and T. Provder, Multidimensional Spectroscopy of Polymers. Vibrational, NMR, and Fluorescence Techniques ACS Symposium Series No. 598, American Chemical Society, Washington, 1X7 (1995). 

From these equations one can approximate kf for benzophenone to be 5 x 10s sec-1. This, however, is the expected rate constant for fluorescence, which should be in competition with radiationless deactivation of the excited state kd. In actuality no fluorescence is observed for benzophenone although the fluorescence techniques are sensitive enough to detect fluorescence occurring with a quantum yield as low as 0/ = 0.001. Therefore kd must be at least 1000 times greater than kf We have... 

Gunasekera,T. S. Veal, D. A. Attfleld,P. V. Potential for broad applications of flow cytometry and fluorescence techniques in microbiological and somatic cell analyses of milk. Int. J. Food Microbiol. 2003, 85, 269-279. 

Mattson S, Christoffersson JO, Jonson R, et al. 1987. X-ray fluorescence technique for in vivo analysis of "natural" and administered trace elements. In Elis, Yasumuru, Morgan, eds. In vivo body composition studies. New York, NY Brookhaven National Laboratory, The Institute of Physical Sciences in Medicine. 

Fluorescence techniques are the most sensitive. With proper dye selection and proper experimental conditions, the absolute sensitivity may reach the limit of single molecules. This feature is especially needed if the target exists in trace amounts. High sensitivity may allow avoiding time-consuming and costly target-enrichment steps. 

The term nonlinear optical property refers to an optical property, which can be modified by exposing the material to intense light irradiation. In this section, we focus on the cascaded first- (/ 1 ) and third-order ( / ) susceptibilities describing nonlinear absorption (ESA and 2PA) and nonlinear refraction (n2) processes. Z-scan, pump-probe, and two-photon upconverted fluorescence techniques are among the most used experimental methods for determining optical nonlinearities. 

Karnaukhov V.N, Yashin V.A. and Krivenko V.G. (1985). Microspectrofluorimeters. Proceedings of First Soviet -Germany International Symposum. Microscopy, Fluorimetry and Acoustic Microscopy. Moscow, p.160-164. Reigosa Roger, M.J. and Weiss, O. (2001). Fluorescence technique. In Handbook of Plant Ecophysiology Technique, (Ed., M.J. Reigosa Roger) Pp. 155-171. Kluwer Academic Publishers, Dordrecht. 

A variety of methods for the measurement of such binding are discussed, including the use of radiolabeling, and immunological and fluorescence techniques. The structures of some of the DNA adducts which have been characterized to date are also described. 

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