Fluorescence intensity measurements

On continued excitation in the phase fluorimeter, the fluorescence lifetime of polymer 1 films also decreased with time. The lifetime decrease was exponential with an average loss constant of 8.2 1.2 x 10 lf sec-1 (1.5 pm thick film) from measurements at different sites on the film. These findings constitute direct evidence for RET from the polymer to a photoproduct(s) in support of the fluorescence intensity measurements. 

The amount of PS taken up by the Y79 retinoblastoma cells was first determined by fluorescence intensity measurements (reflecting the internalized drug concentration)... 

It is recommended, whenever possible, to carry out ratiometric measurements, i.e. to determine the ratio of the fluorescence intensities measured at two wavelengths according to the following methods ... 

Immunoassays based on phase-modulation spectroscopy have been implemented by two distinctly different approaches. Phase-resolved immunoassays rely on fluorescence intensity measurements, in which the emission of one fluorescent species in a mixture is suppressed, and the remainder is quantitated. Phase fluorescence immunoassays utilize measurements of the phase angle and modulation, which change in response to fluorescence lifetime changes. Common aspects of the theory and instrumentation are discussed in this section, followed by individual discussions of the different approaches. 

All fluorescence intensity measurements described here were performed using a Perkin-Elmer LS-50B luminescence spectrometer. Some of the methods were adapted to much smaller volumes using 96-well plates and the Bio-Tek Synergy HT multiwell plate reader (equipped with KC-4 software) (Bio-Tek Instruments, Winoaski, Vermont, U.S.A.). 

The intensity of anthracene fluorescence from liquid methyl methacrylate was examined over a wide range of concentrations. The fluorescence intensity measured following excitation at 350 nm was observed to be linear with anthracene concentration up to a mass fraction of 3 x 10 % anthracene in MMA. Experimental measurements were made with this concentration of anthracene in the liquid component of the cement. Fluorescence spectra... 

Contaminants in protein samples, including lipids and fluorescent material, interfere with the fluorescence intensity measurements. For some probes, especially weakly acidic dissociable probes such as rz.v-parinarate, extreme pH cannot be used, as the quantum yield is different from that in an undissociated form at low pH. Also, sometimes the purity of probes critically affects the fluorescence intensity, thus requiring purification of the probes. 

Optical devices have also been used as transducers. Laser fiber-optics allows high intensity light to travel a long distance using fibrous size carrier. The stable and intense light beam not only provides calibration stability but also makes all the detecting techniques faster and more sensitive. In addition to the UV-VIS absorbance and fluorescence intensity, measurements of multiple reflections, surface plasmon resonance, and total internal reflection fluorescence had recently been used (12, 13, 14). 

Ogner [1] has described an automated analyser method for the determination of boron-containing anions in plants. This is based on the formation of a fluorescent complex between these anions and carminic acid at pH 7. The plant tissues are ashed at 550 °C and the residue dissolved in 0.5 N hydrochloric acid prior to adjustment to pH 6-7 with sodium carbonate solution. The solution is excited at 470 nm and fluorescence intensities measured at 585 nm. Interferences by the reaction of some cations with carminic acid are overcome by passing the solution through an ion exchange column to exchange the cations for sodium ions. Analytical recoveries of boron anions were in the range 98-104%. The detection limit of the method was 5 xg/l boron. 

Figure 1.32 Qualitative mixing performance by plotting the non-calibrated fluorescence intensity measured near the outlet of the mixing chamber along a cross-sectional line as a function of the position on this line. The mixing performances are shown before (gray curve) and after (black curve) the ultrasonic action. Position 0 refers to the top of the mixing [22] (by courtesy of Elsevier Ltd.).

From the fluorescence intensity measurements it is therefore possible to determine... 

Molecule Protonation (P) or Deprotonation (D) P (So) Forster cycle calculations Fluorescence intensity measurements pK(Ti) Forster cycle calculations Ref... 

A typical arrangement of the apparatus used for fluorescent intensity measurements in mixtures of alkali vapors and quenching gases is shown in... 

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