Introduction - Determination of Anions in Natural and Treated Waters - page 7

wavelength range of 230-720nm and an emission wavelength range of 250-800nm.
These instruments feature keyboard entry of instrument parameters which combined
with digital displays, simplifies instrument operation. A high-output pulsed xenon lamp,
having low power consumption and minimal ozone production, is incorporated within the
optical module.
Through the use of an RS 232C interface, both instruments may be connected to
Perkin-Elmer computers for instrument control and external data manipulation.
With the LS-5B instrument, the printing of the sample photomultiplier can be delayed
so that it no longer coincides with the flash. When used in this mode, the instrument
measures phosphorescence signals. Both the delay of the start of the gate (t d ) and the
duration of the gate (t k ) can be selected in multiples of 10µs from the keyboard. This
corrects excitation and emission spectra. Delay times may be accurately measured by
varying the delay time and noting the intensity at each value.
Specificity in luminescence spectrometry is achieved because each compound is
characterised by an excitation and emission wavelength. The identification of individual
compounds is made difficult in complex mixtures because of the lack of structure from
conventional excitation or emission spectra. However, by collecting emission an
excitation spectra for each increment of the other, a fingerprint of the mixture can be
obtained. This is visualised in the form of a time-dimensional contour plot on a three-
dimensional isometric plot.
Fluorescence spectrometers are equivalent in their performance to single-beam
ultraviolet-visible spectrometers in that the spectra they produce are affected by solvent
background and the optical characteristics of the instrument. These effects can be
overcome by using software built into the Perkin-Elmer LS-5B instrument or by using
application software for use with the Perkin-Elmer 3700 and 7700 computers.
Perkin-Elmer LS-2B micro filter fluorimeter
The model LS-2B is a low-cost easy-to-operate, filter fluorimeter that scans emission
spectra over the wavelength range 390-700nm (scanning) or 220-650nm (individual
interferences filters). The essentials of a filter fluorimeter are as follows:
• a source of ultraviolet/visible energy (pulsed xenon)
• a method of isolating the excitation wavelength
• a means of discriminating between fluorescence emission and excitation energy
• a sensitive detector and a display of the fluorescence intensity.
The model LS-2B has all these features arranged to optimise sensitivity for
microsamples. It can also be connected to a highly sensitive 7µL liquid chromatographic
detector for detecting the constituents in the column effluent. It has the capability of
measuring fluorescence, time-resolved fluorescence and bio- and chemiluminescent
signals. A 40-portion autosampler is provided. An excitation filter kit containing six
filters—310, 340, 375, 400, 450 and 480nm—is available.
1.1.2.4 Infrared and Raman spectrometry
Both these techniques have only limited application to the analysis of water samples.