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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 ?
The basic idea of using GALT to assess Gal-1-P in erythrocytes was extended to measuring the product of the reaction, [alpha]-D-glucose 1-phosphate (Glu-1-P), after enzymatic conversion to D-glucose 6-phosphate (Glu-6-P) and treatment with Glu-6-P dehydrogenase to form NADH, which was measured fluorometrically (8), or by determining the radioisotope content of the Glu-1-P when [sup.
The complex formed with 2-thiobarbituric acid was extracted with 5 mL of butanol and quantified fluorometrically (excitation, 515 nm; emission, 553 nm).
NADPH formed by the reaction was measured fluorometrically at 25[degrees]C in 10-mm pathlength quartz cuvettes using a Perkin-Elmer 650-40 fluorescence spectrophotometer.
These instruments, for example, the LightCycler[TM] (Roche Molecular Biochemicals), fluorometrically monitor real-time formation of PCR products during thermal cycling with SYBR Green I.
AlaAP, ArgAP, and CysAP were measured fluorometrically using alanyl-[beta]-naphthylamide (AlaNNap), arginyl-[beta]-naphthylamide (ArgNNap), and cystinyl-[beta]-naphthylamide (CysNNap) as substrates, according to the modified method of Greenberg (10).
A similar method, which uses peptide nucleic acid probes as allele-specific primer inhibitors in combination with the LightCycler that fluorometrically monitors real-time formation of the amplicon with Sybr Green I, was described recently but only for the detection of the Cys282Tyr mutation (16).
The analyte was detected fluorometrically (excitation wavelength, 295 nm; emission wavelength, 400 nm) utilizing its natural fluorescence.
Only one of our abnormal plasmas was scanned fluorometrically using the technique of Poh-Fitzpatrick (29), and in this plasma, an emission peak was prominent at 636 nm, which is characteristic of this disease (12).
The GA activity was determined fluorometrically using L-aspartic acid (3-(7-amino4-methylcoumarin), from Bachem AG, as substrate (12).
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 concentrations were determined fluorometrically following acetone extraction (Strickland & Parsons 1972).