Ocean Optics DTS - Manual (Page 49)

Measuring the Spectrum of a Sample
Polychromix DTS TM Near-Infrared Spectrometer 6-3
Operator’s Manual
Document Number 04-91-0201-00 Rev A
6.2.3 Collecting a Spectrum
To collect a spectrum:
a) Place a cuvette containing the reference sample in the sample holder and
collect the background spectrum as described in Section 5.2.1.
The reference sample should contain everything in the sample except the
compound(s) of interest. As an example, if the sample is dissolved in
methanol:water (1:1), that solvent should be used as the reference
sample. Similarly, if the sample is dissolved in a buffer, the buffer should
be used as the reference sample.
NOTE: If appropriate, the background spectrum can be taken using an
empty cuvette.
b) Remove the reference sample, place the sample in the sample holder
and collect the transmittance or absorbance spectrum as described in
Section 4.2. A plot of Transmission vs. Wavelength or Absorbance vs.
Wavelength will be presented.
6.2.4 Standards
The spectrum of a standard should be collected on a periodic basis (in many
laboratories, a sheet of a polymer is employed as a standard). The standard
should have a number of absorbance bandsspread 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.
6.2.5 Sample Related Spectra Issues
If the instrument appears to be working in an acceptable manner (e.g. the
spectra of the standard is acceptable) and unacceptable sample spectra are
obtained, it is probable that the difficulty is related to the sample. Typical
sample related issues are indicated in Table 6-1. General instrument
troubleshooting is discussed in Chapter 7.