Ocean Optics DTS - Manual (Page 51)

Measuring the Spectrum of a Sample
Polychromix DTS TM Near-Infrared Spectrometer 6-5
Operator’s Manual
Document Number 04-91-0201-00 Rev A
6.3 Using an Integrating Sphere
An integrating sphere is normally used when the analyst wants to obtain the
spectrum of the surface of a solid or a turbid solution. The sample is placed
on the orifice of the sphere and is an integral part of the optical pathway.
6.3.1 The Sample
The following points regarding sample handling should be noted to ensure
the fidelity of collected spectra:
•
Do not get fingerprints on the surface of the sample. If you accidentally
touch the surface, wipe it off with a lint free tissue saturated with methanol
and allow the methanol to evaporate.
•
If a sample is contained in a bottle (flask, etc.) make certain that the
surface through which the infrared radiation passes is clean and is not
scratched, chipped or cloudy.
•
If the sample is believed to be homogeneous, collect spectra at a few
positions on the sample to ensure that you are viewing a representative
sample.
•
If the sample contains imperfections due to handling (e.g. scratches on a
piece of plastic) avoid the areas containing the imperfections.
6.3.2 Collecting a Reflectance Spectrum
To collect a spectrum:
a) Collect the background scan of an appropriate high reflectance material
such as “Spectralon” polymer or roughened gold as described in Section
5.2.
b) Place the sample on the integrating sphere and measure the reflectance.
6.3.3 Standards
The spectrum of a standard should be collected on a periodic basis. The
standard should have a number of absorbance bands spread across the
spectral region. When the spectrum of a standard is collected, the analyst
should check that the intensity of the bands and the wavelength remains
constant over time.
If difficulties are observed with the system, the spectrum of a standard should
be collected and compared to spectra that have been previously collected
using the same conditions.