Chapter 1 Principles, Description, and Functions of the IRAffinity-1
1-16
IRAffinity-1
With FTIR the S/N ratio is defined as the variation near 2200 cm
-1
on the 100%T line. For infrared spectrums, to
avoid obstruction from water vapor peaks (near 4500 - 3500 cm
-1
and 2100 - 1300 cm
-1
) and carbon dioxide
peaks (near 2400 - 2300 cm
-1
), the noise in the unaffected range near 2200 cm
-1
is used (2250 - 2050 cm
-1
).
The S/N ratio is therefore measured and calculated by the following method with IRAffinity-1 series.
1. BKG scan and Sample scan is sequentially measured at 4 cm
-1
resolution, and 2.8 mm/s mirror speed
with 45 accumulations (1minute scan). A 100%T line is obtained.
2. Eliminate winding and slope on the spectrum.
3. The best peak-to-peak value (P-Pmax = noise quantity) of any 50 cm
-1
section within the 2250 -
2050 cm
-1
range is found.
4. The S/N ratio is then calculated by (100/P-Pmax).
5. The average of 10 S/N ratios are used for the instrument check.
1.7 S/N Ratio
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