Fluorescence Spectrometer
The fluorescence spectrometer is a complex instrument comprising (in its simplest form) a broad band light source, a monochromator, a sample cell, an appropriate grating, a diode array sensor and associated electronics. Light from the source passes through the monochromator and the excitation light wave length is selected. The excitation light is focused onto the sample contained in a suitable cell and the fluorescent light is focused onto the grating and thence onto a diode array sensor. The monochrometer is programmable and so either the fluorescence spectrum of the solute at a fixed excitation wavelength can be obtained or an emission spectra obtained at a fixed fluorescence wavelength can be recorded. The system is extremely versatile, but unfortunately emission and fluorescence spectra are not very useful for structure identification. However, they can be used very effectively to confirm substance identity.
Author: RPW Scott
Book:Gas Chromatography - Tandem Techniques
Section:GC-Tandem GC-Spectroscopic-Systems UV-Visible-Absorption-Measurement Multi-Wavelength-Dispersive-Spectrometer
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The UV spectrometer used for monitoring the eluent from a GC column employs a source that provides light over a wide range of wavelengths and consequently, with the aid of an appropriate optical scanning system, absorption spectra of any substance eluted from a gas chromatograph can be obtained for identification purposes. The actual procedure, however, differs with the type of spectrometer being used.
There are two basic types of UV spectrometer, the dispersion spectrometer and the diode array spectrometer, the latter being the more popular for use in conjunction with the gas chromatograph. Both types require a broad emission light source such as the deuterium or the xenon lamps the use of the deuterium lamp being the most widespread. The two types of spectrometers have important differences. In the dispersive instrument the light is dispersed before it enters the sensor cell and thus virtually monochromatic light passes through the sensor. However, if
GC-Tandem GC-Spectroscopic-Systems UV-Visible-Absorption-Measurement Multi-Wavelength-Dispersive-Spectrometer
Author: RPW Scott
Book:Gas Chromatography - Tandem Techniques
Section:GC-Tandem Fluorescence-Spectrometer
fluorescence spectrometer must be fitted with a sensor cell of appropriate dimensions. Such a spectrometer system can be highly complex and versatile and allows excitation spectra to be obtained at any fixed fluorescent wavelength or emission spectra to be obtained for any fixed excitation wavelength. In general fluorescence spectra have very limited use in structure elucidation but can be used for identification purposes providing the necessary reference spectra are available. A diagram of a fluorescence spectrometer is shown in figure 13. It consists of two monochromators, the first that selects the wavelength of the excitation light and the second disperses the fluorescent light and provides a fluorescence spectrum. The spectrometer incorporates two distinctly different light paths and as a result the optical system appears quite complicated. If the different light paths are considered separately, that is firstly, the path of the excitation light and secondly, the path of the
GC-Tandem Fluorescence-Spectrometer
Author: RPW Scott
Book:Gas Chromatography - Tandem Techniques
Section:GC-Tandem GC-Spectroscopic-Systems
reference compound and, if a match is obtained (the difference is close to zero) the unknown is considered identified. In a similar manner, for certain compounds, UV and fluorescence spectra can also be used to confirm solute identity and the association of the GC with a UV spectrometer or a fluorescence spectrometer has proven to be much easier due to the significantly greater sensitivity of these spectrometers compared with that of the IR spectrometer.
The use of UV spectra and fluorescence spectra, however, are far less useful than mass spectra or IR spectra for solute identification. Except for certain substances (e.g. those containing aromatic rings) the majority of compounds give very similar UV spectra with very little fine structure to allow confident spectra matching. This is due to a multiplicity of adsorption bands merging to produce a broad envelope the cause of which will be discussed later. Similarly fluorescence spectra have much less detail than IR
GC-Tandem GC-Spectroscopic-Systems
Author: RPW Scott
Book:Liquid Chromatography Detectors
Section:HPLC-Detectors Fluorescence Multi-Wavelength-Fluorescence
The Multi Wavelength Fluorescence Detector
The multi
wavelength fluorescence detector contains two monochromators, one to select the
excitation wavelength and the second to select the fluorescence wavelength or
produce a fluorescence spectrum A diagram of the multi wavelength fluorescence
detector is shown in figure 38.
Figure 38. The
Fluorescence Spectrometer Detector
The detector
comprises a fluorescent spectrometer fitted with suitable absorption cell that
is sufficiently small so as not to degrade the resolution of an LC column. There are
HPLC-Detectors Fluorescence Multi-Wavelength-Fluorescence
Author: RPW Scott
Book:Liquid Chromatography Detectors
Section:HPLC-Detectors Fluorescence Single-Wavelength-Excitation
3. Acenaphthene
4. Phenanthrene
5. Anthracene
6. Fluoranthracene
7. Pyrene
8. Benzo(a)anthracene
9. Chrysene
10. Benzo(b)fluoranthene
11. Benzo(k)fluoranthene
12. Benzo(k)fluoranthene
13. Dibenz(a,h)anthracene
14.Indeno(1,2,3,cd)pyrene
15. Benzo(ghi)perylene
Courtesy of the Perkin Elmer Corporation
Figure 37.
Separation of the Priority Pollutants Monitored by the Simple Fluorescence
Detector
There are some
compromises between the expensive fluorescence spectrometer detector and the
single wavelength excitation fluorescence detector. Some have a single
monochromators that select the wavelength of the excitation light, others
employ a single monochromator to select the emission wavelength or provide
emission spectra
HPLC-Detectors Fluorescence Single-Wavelength-Excitation
Author: RPW Scott
Book:Liquid Chromatography Detectors
Section:HPLC-Detectors Fluorescence
the removal of
any stray scattered incident light.
The
fluorescence signal (If) is given by
where (f)
is the quantum yields (the ratio of the number of photons emitted and the number of
photons absorbed),
(Io)
is the intensity of the incident light,
(c)
is the concentration of the solute,
(k)
is the molar absorbence,
(l)
is the path length of the cell.
Fluorescence
detectors can be simple or complex, the simplest consists of a single
wavelength excitation source and a sensor that monitors fluorescent light
of all wavelengths. For certain samples, this form of fluorescence detector can
be very sensitive and relatively inexpensive. However, employing excitation
light of a single wavelength and only a broad emission wavelength, it is not
very versatile. Conversely, the fluorescence spectrometer fitted with a small
sensor cell is far more
HPLC-Detectors Fluorescence