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An instrument that measures the fluorescent radiation emitted by a sample which is exposed to monochromatic radiation, usually radiation from a mercury-arc lamp or a tungsten or molybdenum x-ray source that has passed through a filter; used in chemical analysis, or to determine the intensity of the radiation producing fluorescence. Also spelled fluorimeter.



(also fluorimeter), an instrument used for measuring the decay time τ of fluorescence, which is approximately 10–8–10–9 sec. A fluorometer operates on the following principle. During high-frequency modulated excitation of luminescence, the luminescence is modulated at the same frequency as the excitation; however, because of the finite duration of the luminescence emission, the phase of the luminescence modulation lags behind that of the excitation modulation. In the case of excitation that is sinusoidally modulated at a frequency ω and fluorescence that decays exponentially, the phase angle φ = tan–1 (ωτ). The relation between the amplitude A0 of the excitation modulation and the amplitude A of the luminescence modulation is Fluorometer. Thus, to determine τ either φ or the ratio A0/A must be measured. If the decay is not exponential, the same method may be used to establish the mean lifetime of the excited state and to estimate the extent to which the decay is not exponential.

Figure 1. Schematic diagram of a phase fluorometer

The most widely used fluorometers are phase fluorometers, which measure φ (Figure 1). In an optical-excitation phase fluorometer, a light beam from a source (1) is focused on a modulator (2). A portion of the modulated flux is deflected by a semi-transparent plate (3) and enters a photomultiplier (5). The remainder of the flux is focused on a specimen (4) to excite fluorescence, which is deflected to another photomultiplier (6). The phase difference φ between the photoelectric currents from (5) and (6) is measured by means of a phase meter (7). A cathode-ray tube or phase detector (8) serves as the phase indicator. Fluorometers based on electron-beam and X-ray excitation have also been developed.

In an instrument that is more advanced than a fluorometer, luminescence is excited by short light pulses, and the decay curve is recorded directly.

Instruments that are used for luminescence analysis are also called fluorometers, or fluorimeters. Such instruments measure the intensity of luminescence and contain both a source for exciting the luminescence and a photometer.

References in periodicals archive ?
Immune response was measured by quantifying NO fluorometrically in host tissue or in anemone homogenates by confocal microscopy or DAN assay respectively (described below).
We measured the activities of 7-ethoxyresorufin O-dealkylase (EROD) and 7-pentoxyresorufin O-dealkylase (PROD) by monitoring the production of resorufin fluorometrically according to the method of Burke et al.
AP was determined fluorometrically, using methylumbelliferyl-phosphate (MUP) as a model substrate.
Purified DNA was placed in 1X TE buffer and quantified fluorometrically.
Chlorophyll a and phaeopigment con centrations were determined fluorometrically (Parsons et al.
The release of AFC or AMC from the substrates was measured fluorometrically using a Tecan Satire 11[TM] (Crailsheim, Germany) with an emission/excitation wavelength of 400/505 nm for AFC and with 380/460 nm for AMC.
The concentration of DNA in each sample was fluorometrically quantified using PicoGreen dsDNA quantitation reagent (Invitrogen) against a standard curve of Lambda-phage DNA on a Stratagene MX3000P qPCR system.
45-[micro]m membrane filters (28 mm) and stored at -20[degrees]C before being analyzed fluorometrically (Turner Designs-10) according to Parsons et al.
After separation and postcolumn reduction with platinum reactor, we measured the reduced form of phylloquinone (hydroquinone) fluorometrically by use of a programmable fluorescence detector (model 2475) with excitation and emission wavelengths of 244 and 420 run, respectively.
42 and Se in the filtrate was analysed fluorometrically (Bio-Rad's VersaFluor[TM] Fluorometer).
After exposure to rhodamine B and test compounds, the dye was extracted from the biopsy tissue disks in a defined volume of solvent, and the amount of dye was then measured fluorometrically.
Chlorophyll a concentration was measured fluorometrically after overnight extraction in acetone (4).