Inner-filter effect

In addition, Montenegro et al., (2007) determined that the photosensitized RF-mediated degradation of vitamins A, D3, and RF itself in skimmed milk was strongly reduced by the addition of small amounts of lycopene-gum arabic-sucrose microcapsules, prepared by spray-drying. Under these conditions, the bulk properties of the skimmed milk were unmodified. The main photoprotection mechanism of the milk vitamins was the efficient quenching of the 3Rf by the protein moiety of GA. Small contributions (<5%) to the total photoprotection percentage was due to both inner filter effect and 1O2 quenching by the microencapsulated lycopene. 

Here use is made of the approximation ecdl0 a / for OD < 0.05. Low concentrations of both compounds must be used to avoid absorption of the emitted light by an inner filter effect. 

Energy transfer by the trivial mechanism is characterized by (a) change in the donor emission spectrum (inner filter effect), (b) invariance of the donor emission lifetime, and (c) lack of dependence upon viscosity of the medium. 

Use of an algorithm to eliminate the inner-filter effect in a bioreactor 194... 

Some of these problems can be overcome with a different calorimetric design (see later discussion). Other problems, which are more dependent on the chemistry and physics of the process under study than on the instrumentation, require careful attention. Unnoticed side reactions or secondary photolysis are examples, but one of the most serious error sources in photocalorimetry is caused by the quantum yield values, particularly, as explained, when they are small. Unfortunately, many literature quantum yields are unreliable, and it is a good practice to determine n for each photocalorimetric run. Errors in

photon absorption by reaction products. 

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. 

Radiative transfer results in a decrease of the donor fluorescence intensity in the region of spectral overlap. Such a distortion of the fluorescence spectrum is called the inner filter effect (see Chapter 6). 

Attention should be paid to possible problems in the measurement of fluorescence quantum yields (some of which are discussed Section 6.1.5) inner filter effects, possible wavelength effects on Op, refractive index corrections, polarization effects, temperature effects, impurity effects, photochemical instability and Raman scattering. 

Pitfalls in steady-state fluorescence measurements inner filter effects and polarization effects... 

Emission inner filter effect (self-absorption) The fluorescence photons emitted in the region overlapping the absorption spectrum can be absorbed (radiative energy trans-... 

Inner filter effects due to the presence of other substances When the solution contains other chromophores that absorb light in the same wavelength range as the fluorescent compound under study, the chromophores act as filters at the excitation wavelength and the fluorescence intensity must be multiplied by a correction factor. If the chromophores do not interact with the fluorescent compound, the correction factor is simply the fraction of light absorbed by the compound at the chosen excitation wavelength, so that the corrected fluorescent intensity is given by ... 

All these inner filters effects are difficult to correct and it is advisory to work as much as possible with dilute solutions. 

The factor A/Ap arises from the contribution of the acceptor moiety to the overall absorption at the excitation wavelength 7p. Attention should be paid to the inner filter effect caused by absorption of the acceptor at the emission wavelength of the donor. Some correction may be necessary. 

Time-resolved emission of the donor or acceptor fluorescence provides direct information on the transfer rate, without the difficulties that may result from inner filter effects. 

H. He, H. Li, G. Mohr, B. Kovacs, T. Wemer, and O. S.Wolfbeis, Novel type of ion-selective fluorosensor based on the inner filter effect An optrode for potassium, Anal. Chem, 65, 123-127... 

S. P. Srinivas and R. Mutharasan, Inner filter effects and their interferences in the interpretation of culture fluorescence, Biotech, and Bioeng. 30, 769-774(1987). 

Inner-filter effects. The absorption of the fluorescence excitation and emission by the specimen is referred to as the "inner-filter" effect this effect has been treated in the literature (24-27). The inner-filter effect reduces the signal levels and distorts the emission spectrum and the intensity-concentration relationship. The effect is more pronounced in right-angle fluorescence measurements (27) than in the "front face" configuration in which the fluorescence is viewed from the same side as the excitation beam. 

---