horiba FluoroMax-3, Руководство по эксплуатации

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FluoroMax-3 v. 3.1 (3 Mar 2006) System Operation
3-14
Note:
Make sure the
test is carried out
with the actual de-
tector you will be us-
ing. All Spex
®
sys-
tems’ parameters
are specified with a
R928P photomulti-
plier tube at room
temperature.
Calculation of water-Raman signal-to-noise ratio
Introduction
The water-Raman test is a good measure of relative sensitivity between different in-
struments, if the experimental conditions used to compare the systems are the same.
Unfortunately, there are different ways of handling the data, all of which are valid but
which will give quite different values. Therefore, it is important not only to know how
the water-Raman
S
/
N
values are measured, but also how the data were treated. The wa-
ter Raman
S
/
N
test method combines a value for system sensitivity (a signal) with a
value for system noise (no signal) to show the overall performance of the instrument.
Definitions
At HORIBA Jobin Yvon, we define the
S
/
N
ratio as the difference of peak and back-
ground signal, divided by the square root of the background signal.
S
N
S S
S
peak background
background
=
−
Our method
The peak signal is measured at the water-Raman peak (397 nm for 350 nm excitation)
and the noise in a region (450 nm) where no Raman signal is present. An “ideal” sys-
tem would give a signal value of zero at 450 nm. Thus the equation becomes
S
N
S S
S
=
−
397 450
450
nm nm
nm
Another commonly used method is to divide the difference (peak signal minus back-
ground signal) by the rms value of the noise on the background signal. This second
method is used by a few other manufacturers:
S
N
S S
N
peak background
rms background
=
−
,
Other manufacturers’ method
Example
Some actual data from a Fluorolog
®
FL3-11 system (a typical system, a few years old)
serve to show the difference between the two methods. The experimental conditions
were as follows:
Excitation
350 nm with 5 nm bandpass
Emission 360–450 nm with 5 nm bandpass
Increment 1 nm
Integration time 1 s
No smoothing of data points
Standard room-temperature, red-sensitive detector