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Experiment Tutorial
When you are ready to begin your experiment, you should have already installed the PC2000, installed
OOIChem, set up your light source/sample holder, and connected your fiber from the PC2000 to your light
source/sample holder.
Now you are ready to take your measurements. Because of the components making up your CHEM2000 and
CHEM2000-UV-VIS, your system is ideal for absorbance and transmission. The CHEM2000 can also make
relative irradiance measurements. If, however, you wish to utilize your system for other measuring functions,
additional products might be required. Contact an Ocean Optics Applications Scientist for options.
Absorbance Experiments
Absorbance spectra are a measure of how much light is absorbed by a sample. The software calculates
absorbance (
A
λ
) using the following equation:
S
λ
-
D
λ
A
λ
= - log
10
(
R
λ
-
D
λ
)
where
S
is the sample intensity at wavelength
λ
,
D
is the dark intensity at wavelength
λ
,
R
is the
reference intensity at wavelength
λ
.
Common applications include the quantification of chemical concentrations in aqueous or gaseous samples.
To take an absorbance measurement:
1.
Select
Scope
under
Mode of Operation
in the software display area. Make sure the signal is on scale.
Adjust acquisition parameters so that the peak intensity of the reference signal is about 3500 counts. Take
a reference spectrum by first making sure nothing is blocking the light path going to your spectrometer.
The analyte you want to measure must be absent while taking a reference spectrum. Take the reference
reading by clicking the
Reference
button in the software display area. (This command merely stores a
reference spectrum. To save a spectrum, you must select
File | Save Spectral Values
from the menu.)
Storing a reference spectrum is requisite before the software can calculate absorbance spectra.
2.
While still in
Scope Mode
, take a dark spectrum by first completely blocking the light path going to
your spectrometer. (If possible, do not turn off the light source. If you must turn off your light source
to store a dark spectrum, make sure to allow enough time for the lamp to warm up before continuing
your experiment.) Take the dark reading by clicking the
Dark
button in the software display area.
(This command merely stores a dark spectrum. To save a spectrum, you must select
File | Save
Spectral Values
from the menu.) Storing a dark spectrum is requisite before the software can calculate
absorbance spectra.
3.
Begin an absorbance measurement by first making sure the sample is in place and nothing is blocking
the light going to your sample. Then select
Absorbance
under
Mode of Operation
in the software
display area. Click on the
Scan
button in the display area to take a scan. If
Single
is selected, only one
scan will be taken. If
Continuous
is selected, the spectrometer will continuously take scans until you
click on the
Stop
button. To save the spectrum, select
File | Save Spectral Values
from the menu.
!
!
!
!
If at any time any sampling variable changes -- including integration period, averaging, boxcar
smoothing, distance from light source to sample, etc. -- you must store a new reference and
dark spectrum.
