Global Lifetime Analysis
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- Written by Chavdar Slavov
Typically, in time-resolved spectroscopy the multiple kinetic traces recorded in dependence of wavelength or other experimental variable are analyzed simultaneouslyi in a procedure called global analysis. The most common global analysis procedure is global lifetime analysis (GLA), where the experimental data is approximated by a discrete sum-of-exponentials function. The global parameters spanning the dataset are the lifetimes, while the pre-exponential amplitudes are determined for each kinetic trace. GLA results in the so-called decays-associated spectra (DAS), where the pre-exponential amplitudes for each lifetime component are plotted against an experimental variable, e.g. detection wavelength. The DAS is a compact representation of the kinetic information in the data.
Lifetime Density Analysis
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- Written by Chavdar Slavov
The great number of spatial, energetic and temporal degrees of freedom of the studied molecule ensembles and their matrix produces a continuous distribution of individual exponential decays. In this respect, the approximation of the data profile by a discrete set of exponentials (GLA and GTA) must be interpreted as a curve parameterization, concealing potential contribution of a larger number of underlying decays. Within lifetime density analysis (LDA) a quasi-continuous sum-of-exponents function is used to perform model-independent analysis of the experimental data. The methods yields a lifetime density/distribution map (LDM) which gives a comprehensive overview of the kinetics.
Global Target Analysis
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- Written by Chavdar Slavov
Global target analysis (GTA) is the more general case of global analysis, where kinetic models are directly tested for compliance with the time-resolved data. GTA is essential, because kinetic modeling is the only quantitative way to reveal reaction mechanisms. In essence, GTA consists of devising a kinetic reaction scheme based on previous knowledge about the studied system and certain assumptions. The kinetic scheme is then represented by a system of differential equations. The solution of such a system of differential equations for first-order kinetics is a sum-of-exponentials function similar to the one used in GLA, with the difference that now the lifetimes depend in a complex manner, defined by the kinetic model, on the kinetic rates. An important parameter that emerges from GTA is the species-associated spectrum (SAS), which physically represents the stationary spectra of the model compartments as if they were measured separately.
Artifact analysis
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- Written by Chavdar Slavov
Time-resolved data from ultrafast optical spectroscopy is typically contaminated by different experimental artifacts which hinders the straightforward analysis. Thus, the analysis procedures need to include algorithms for instrument response deconvolution, wavelength dependence of the time-zero position of the recorded signal and of the width of the instrument response function (IRF), coherent artifact analysis, etc.