Fluorimetry fluorescence

Fluorimetrie fluorescence analysis, fluorimetry Fluoreszenzibschung fluorescence quenching Fluoreszenzsonde/... 

Fluorimetrie fluorescence marker Fluoreszenz sonde, Fluoreszenzmarker fluorescence quenching Fluoreszenzloschung... 

Fluorimetry is generally used if there is no colorimetric method sufficiently sensitive or selective for the substance to be determined. In inorganic analysis the most frequent applications are for the determination of metal ions as fluorescent organic complexes. Many of the complexes of oxine fluoresce strongly aluminium, zinc, magnesium, and gallium are sometimes determined at low concentrations by this method. Aluminium forms fluorescent complexes with the dyestuff eriochrome blue black RC (pontachrome blue black R), whilst beryllium forms a fluorescent complex with quinizarin. 

Perez Ruiz et al. [26] determined penicillamine and tiopronin in pharmaceutical preparations by flow injection fluorimetry. The procedure is based on the oxidation of these drugs by thallium(III), whereupon the fluorescence of T1(T) produced in the oxidation of penicillamine is monitored using excitation at 227 nm and emission at 419 nm. A linear calibration graph for penicillamine was obtained between 3 x 10-7 and 8 x 10 5 6 M. 

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. 

In 1867 Goppelsroder introduced the term Fluoreszenzanalyse (analysis by fluorescence or fluorimetry) and proposed the first fluorimetric analysis in... 

Triprolidine hydrochloride in syrups and tablets can be analyzed by fluorimetry. A portion of the tablets or syrup is made basic with IN NaOH and extracted with ethylene chloride. The organic phase is then extracted with 0.1N I SO. The fluorescence of the acid extract is determined with a fluorometer using a UG11 filter for excitation and a Wratten 2A filter for emission. The fluorescence of the sample preparation is compared against a Reference Standard prepared in the same manner22. 

The main advantage of fluorescence techniques is their sensitivity and measurements of nanogram (10—9 g) quantities are often possible. The reason for the increased sensitivity of fluorimetry over that of molecular absorption spectrophotometry lies in the fact that fluorescence measurements use a non-fluorescent blank solution, which gives a zero or minimal signal from the detector. Absorbance measurements, on the other hand, demand a blank solution which transmits most of the incident radiation and results in a large response from the detector. The sensitivity of fluorimetric measurements can be increased by using a detector that will accurately measure very small amounts of radiation. 

The problem of background fluorescence has been largely overcome with the introduction of time-resolved fluorimetry. This technique relies on the use of fluorophores with a long-lived fluorescence which can be measured... 

These systems possess the simplest possible variation in that only one parameter, i.e., the fluorescence quantum yield is proton-controlled. The insulation of the fluor and receptor modules in the ground state by the alkyl spacer leads to essentially pH-invariant absorption (position, shape, and intensity) and fluorescence spectra (shape and position only). The same pKa values are obtained from fluorimetry or absorption spectroscopy so that the detection sensitivity of excited state experiments can be used for the measurement of binding constants of the ground state. 

The application of semiconductor lasers to a broad range of areas in spectrometry has recently been reviewed by Imasaka. 67, 68) Topics covered include photoacoustic, absorption, and thermal lens, as well as steady-state and time-resolved fluorescence. Patonay et al. have reviewed the application of diode lasers to analytical chemistry.(69) The performance of several commercially available laser diodes for fluorimetry has recently been compared. 70 ... 

T. Parassassi, F. Conti, M. Glaser, and E. Gratton, Detection of phospholipid phase separation. A multifrequency phase fluorimetry study of l,6-diphenyl-l,3,5-hexatriene fluorescence, J. Biol. Chem. 259, 14011-14017 (1984). 

M. R. Rainbow, S. Arterton, and R. C. Eberhardt, Fluorescence lifetime measurements using total internal reflection fluorimetry Evidence for a conformational change adsorbed to quartz, J. Biomed. Mater. Res. 21, 539-555 (1987). 

Fluorimetry excels photometry for detecting analytes and products by means of sensors on accoimt of its higher sensitivity and the also higher selectivity arising from the small number of species that can emit previously absorbed energy in a radiant form. As a rule, the fluorescence of an analyte or reaction product increases on retention on a solid support as a result of losses... 

The sorbent materials used to construct this type of sensor are widely varied (ion exchangers, adsorbent solids, polymers) and are employed as particles (larger than 30 pm in order to avoid overpressure in the flow system) or films. Most of these sensors are optical and rely on absorption, reflectance or molecular fluorescence measurements. In order to ensure that the sensing microzone is fully compatible with the detector, the sorbent material used must be as transparent as possible (photometry) or give rise to no appreciable light scatter (fluorimetry) so that the baseline (resulting from passage of the carrier) may be as low as possible. 

It is desirable to have means to measure organohalides such as carbon tetrachloride in situ in water and other environmental media. One approach to doing this has been demonstrated by the in situ analysis of chloroform-contaminated well water using remote fiber fluorimetry (RFF) and fiber optic chemical sensors (FOGS) (Milanovich 1986). With this approach, fluorescence of basic pyridine in the presence of an organohalide (Fujiwara reaction) is measured from a chemical sensor immersed in the water at the end of an optical fiber. Carbon tetrachloride undergoes a Fujiwara reaction, so its determination might be amenable to this approach. 

Progress has been made using the ALA-protoporphyrin IX photosensitiser system in in vivo fluorimetry, because the fluorescent protoporphyrin concentration in tumour cells is much higher than in healthy cells. An example of its use is in the successful diagnosis of bladder tumours, giving superior results to visual examination. Anew generation of pentyl and hexyl esters show an even more intense fluorescence. 

In addition to the techniques already discussed, aspects of MC formation in LB films have been investigated by Rutherford backscattering (RBS) (65) and fluorimetry (17,49,50.76,79,81,83,84). The results from the RBS analysis of H2S-exposed CdAr films provided evidence for the formation of spheroidal CdS particles. Investigations of the fluorescence properties of MC particles in LB films are discussed later. 

These discussions provide an explanation for the fact that fluorescence emission is normally observed from the zero vibrational level of the first excited state of a molecule (Kasha s rule). The photochemical behaviour of polyatomic molecules is almost always decided by the chemical properties of their first excited state. Azulenes and substituted azulenes are some important exceptions to this rule observed so far. The fluorescence from azulene originates from S2 state and is the mirror image of S2 S0 transition in absorption. It appears that in this molecule, S1 - S0 absorption energy is lost in a time less than the fluorescence lifetime, whereas certain restrictions are imposed for S2 -> S0 nonradiative transitions. In azulene, the energy gap AE, between S2 and St is large compared with that between S2 and S0. The small value of AE facilitates radiationless conversion from 5, but that from S2 cannot compete with fluorescence emission. Recently, more sensitive measurement techniques such as picosecond flash fluorimetry have led to the observation of S - - S0 fluorescence also. The emission is extremely weak. Higher energy states of some other molecules have been observed to emit very weak fluorescence. The effect is controlled by the relative rate constants of the photophysical processes. 

B) Phase-shift methods. The phase shift method for determining fluorescence lifetimes is based on the principle that if fluorescence is excited by suitably modulated light source, emitted radiation will also be similarly modulated. With reference to a scattering substance, emission from a fluorescent substance will introduce a time lag due to finite time between absorption and emission. This, by definition is the lifetime of the excited state. The time lag will cause a phase-shift relative to the exciting light. Phase fluorimetry requires a modulated light source and a phase sensitive detector. 

Certain compounds, whether present in solution or in solid state (as molecular or ionic crystals) emit light when they are excited by photons in the visible or near ultraviolet domain of the spectrum. This phenomenon, called luminescence, is the basis of fluorimetry, a very selective and sensitive analysis technique. The corresponding measurements are made with fluorimeters or spectrofluorimeters and, for chromatographic applications, with fluorescence detectors. 

To obtain good results in fluorimetry, solutions must be dilute. Above a given limit, fluorescence is no longer proportional to concentration because of the nonlinearity of Beer-Lambert s law. Excitation is proportionally weaker and association complexes are formed between excited and ground state molecules. This leads to the apparently paradoxical result that fluorescence can diminish as analyte concentration increases (Fig. 12.5). 

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