Concentration on fluorescence

Fig. 8.2 Effect of GdnCl concentrations on fluorescence spectra of B. stearothermophilus alanine racemase.

Figure 37. The effect of increased terephthalate ion (TA) concentration on fluorescence intensity at 20 kHz.

The effect of HP and MHP concentration on fluorescence intensity. The amino acid concentration was fixed, and the MHP concentration varied. This revealed that the fluorescence intensity of the amino acids was remarkably quenched, and the emission wavelength shifted to a shorter wavelength. It was especially remarkable to D, L- (or L-) tryptophan, but the excitation wavelength was unchanged (Fig. 1). 

Effects of quencher concentration on fluorescence lifetime and intensity... 

Fast concentration and sample injection are considered with the use of a theory of vibrational relaxation. A possibility to reduce a detection limit for trinitrotoluene to 10 g/cnf in less than 1 min is shown. Such a detection limit can by obtained using selective ionization combined with ion drift spectrometry. The time of detection in this case is 1- 3 s. A detection technique based on fluorescent reinforcing polymers, when the target molecules strongly quench fluorescence, holds much promise for developing fast detectors. 

Fluorescence measurements are fundamentally different to absorption measurements [20,173,180]. The fluorescence intensity depends only on the population of sample molecules and can be calculated in several ways. Independent of "the method chosen at low sample concentrations the fluorescence signal, F, is adequately described by equation (7.26)... 

A detailed study of the photostability of the DAST-type agent Cl Fluorescent Brightener 85 on cellophane film was carried out recently. The initial fading reaction is a photo-sensitised trans-cis isomerisation of the stilbene grouping. The subsequent oxidative attack on the molecule is concentrated on the vulnerable ethene linkage at the centre of this moiety [39]. 

The sensor for the measurement of high levels of CO2 in gas phase was developed, as well90. It was based on fluorescence resonance energy transfer between 0 long-lifetime ruthenium polypyridyl complex and the pH-active disazo dye Sudan III. The donor luminophore and the acceptor dye were both immobilized in a hydrophobic silica sol-gel/ethyl cellulose hybrid matrix. The sensor exhibited a fast and reversible response to carbon dioxide over a wide range of concentrations. 

Dissolve the purified SPDP-modified dendrimer of step 5 in 50 mM sodium phosphate, 0.15M NaCl, pH 7.5, or in DMSO at a concentration of at least lOmg/ml. Add a 10-20 X molar excess of an amine-reactive fluorescent molecule (i.e., NHS-rhodamine or a hydrophilic NHS-Cy5 derivative see section on fluorescent probes). React with mixing for 1 hour at room temperature. Purify the fluorescently labeled SPDP-modified dendrimer using gel filtration or ultrafiltration. Follow the method of either step 7 or 8 to conjugate the dendrimer to another protein or molecule. 

Sichere et al. [25] determined bromine concentrations in the 0.06-120mg/1 range in brines, directly by X-ray fluorescence using selenium as an internal standard to eliminate interference effects. Lower concentrations of bromine must be concentrated on filter paper containing an ion exchange resin. The same concentrations of chlorine can be determined with the addition of barium to reduce the interferences from carbonates and sulfates. Relative standard deviation was better than 1%. The interference of some other ions (e.g., calcium, potassium, magnesium, sodium, and iron) was examined. 

In 1888, Walter studied the quenching of fluorescence, by the concentration effect, of fluorescein solutions. Nicols and Merrit observed in 1907, in solutions of eosine and resoruflne, the symmetry existing between their absorption and fluorescence spectra. In 1910, Ley and Engelhardt determined the fluorescence quantum yield of various benzene derivatives, values that were still referred to until recent years [18], The works by Lehmann and Wood, around 1910, marked the beginning of analysis based on fluorescence [4],... 

Measurement of fluorescence intensity can be used for quantitative analysis of fluorescent compounds where the intensity of fluorescence is proportional to the concentration of the compound. Because of their high sensitivity and selectivity, analytical techniques based on fluorescence detection are commonly used. If a target compound is fluorescent then direct detection of the fluorescence emitted is possible using a fluorimeter (Figure 4.7). 

Perhaps the most obvious strategy for a chemist is to use an actual chemical reaction involving covalent bond formation rather than the interplay of supramo-lecular forces. The following section thus illustrates the use of chemical reactions in the context of luminescence signaling, concentrating on two different phenomena (i) the production of a fluorophore in a chemical reaction, which still requires a conventional fluorescence measurement setup, and (ii) chemiluminescence (CL), where photons are produced by a chemical reaction, but which only needs a detector for registration of the emitted light. 

Moreover, when the concentration of fluorescent compound is high, inner filter effects reduce the fluorescence intensity depending on the observation conditions (see Chapter 6). In particular, the photons emitted at wavelengths corresponding to the overlap between the absorption and emission spectra can be reabsorbed (radiative transfer). Consequently, when fluorometry is used for a quantitative evaluation of the concentration of a species, it should be kept in mind that the fluorescence intensity is proportional to the concentration only for diluted solutions. 

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