Fluorophores general characteristics

The lifetime, therefore, depends not only on the intrinsic properties of the fluorophore but also the characteristics of the environment. For example, any agent that removes energy from the excited state (i.e., dynamic quenching by oxygen) shortens the lifetime of the fluorophore. This general process of increasing the nonradiative decay rates is referred to as quenching. 

The solubility in water of many fluorophores is achieved by grafting sulfonate groups. Fortunately, these groups only slightly affect the fluorescence characteristics of the parent molecule. In general, there is a small red-shift of the fluorescence spectrum, whose vibrational structure is somewhat blurred, and the fluorescence quantum yield is slightly decreased. 

The ESI-MS characteristics of ohgosaccharides are strongly determined by the identity. The ESI-MS of oligosaccharides is complicated by their hydrophihcity, which limits their surface activity in the ESI droplets. Derivatization strategies to reduce their hydrophihcity, e.g., permethylation or introducing chromophores or fluorophores (Ch. 20.3.5), generally result in an improved response. Permethylated oligosaccharides can be analysed as protonated molecules or as sodium adducts in positive-ion ESI-MS. 

Another mechanism used to manipulate fluorescence characteristics of a fluorophore is called internal charge transfer (ICT). Principles of ICT were first applied in an effort to rationalize increased acidity of phenol." However, until Valeur s reports, generalization of these ideas and systematic exploitation in metal sensing were not realized. 

Principles and Characteristics Atomic and molecular spectroscopy have been revolutionised and revitalised by laser technology. Laser spectroscopy excels in sensitivity and spectral or time resolution. Lasers enable chemists to microprobe systems of fluorophores with an exceptional degree of spectral selectivity, sensitivity, time response, and dynamic range. The four major areas of laser application in analytical atomic spectroscopy, namely LEAFS cfr. Chp. 3.3.1), LA-ICP-AES/MS (cfr. Chp. 3.2.1), LIBS (cfr Chp. 3.3.2) and LEIS, were described by Sneddon etal. [94]. For the types of laser and their general properties which are useful to the analytical atomic spectroscopist, cfr. ref. [95]. 

Principles and Characteristics The analytical capabilities of the conventional fluorescence (CF) technique (c/r. Chp. 1.4.2) are enhanced by the use of lasers as excitation sources. These allow precise activation of fluorophores with finely tuned laser-induced emission. The laser provides a very selective means of populating excited states and the study of the spectra of radiation emitted as these states decay is generally known as laser-induced fluorescence (LIF, either atomic or molecular fluorescence) [105] or laser-excited atomic fluorescence spectrometry (LEAFS). In LIF an absorption spectrum is obtained by measuring the excitation spectrum for creating fluorescing excited state... 

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