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UV-Photo-Florescenceefinition of Terms
2.5
Background Fluorescence
The fluorescence signal due to the probe/analyzer optical
configuration, stray light, and fluorescence from the background
material.
2.6
Sensitivity
The ability of the analyzer to detect a given level of analyte
based on the molecular fluorescence from the analyte. The actual limits
of detection depend on the properties of the analyte measured and the
process conditions. Parameters such as pH, temperature, oxygen content,
and background solvent, to name but a few may dramatically alter the
fluorescence intensity measured. Typically, detection of parts-per-
million (PPM) and parts-per-billion (PPB) analyte levels can be
detected. In general, fluorescent measurements are 1,000 to 500,000
times more sensitive than absorbance based photometric measurements.
Practically, sensitivity means the minimum analyte concentration that
can be measured above background fluorescence in the process.
2.7
Specificity
The ability of the analyzer to monitor one specific analyte in a
mixture of background materials without interference from the
background materials. In absorbance based photometric measurements,
interference problems are common since many materials absorb light,
making it difficult to isolate the targeted analyte in a complex mixture.
However, Fluorometers are highly specific and less susceptible to
interferences because fewer materials exhibit molecular fluorescence.
Furthermore, if background materials do absorb and emit light, it is rare
that they will emit the same wavelength of light as the analyte of
interest.
2.8
Signal-to-Noise Ratio
Signal refers to the emission collected by the fluorescence probe
and monitored by the analyzer using the internal span filter. Noise
refers to the output from the instrument's electronics, which is present
whether or not sample is being read and any collection of errant
wavelengths not removed by the optical filters. Noise is measured by
placing the fluorescence probe in air and in complete darkness (no stray
light). For process monitoring, the signal-to-noise ratio is not as
important as the signal-to background ratio.
Teledyne Analytical Instruments
5
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