6
some of the Varian accessories. You can collect a baseline immediately before
scanning a sample or use a stored baseline.
The accuracy of your baseline determines the accuracy of your measurement.
You should perform a zero/baseline correction before running your samples
after the instrument has warmed up for ~20 minutes using the same scan
parameters that you will use for your sample.
The Cary WinUV system collects a new baseline when you select any type of
baseline correction in the Baseline tab of the Setup dialog box and then click
Baseline
button in the application window. Depending on the type of correction
you have selected, the Cary will prompt you to perform either one or two
baseline scans. The first is a 100%Tbaseline (for the DRA with the 100%
reference material in the sample positions). The second, if required, is a
0%Tbaseline (with the sample beam blocked).
Once the baselines have been collected, they will be automatically applied to
each collected sample data point as it is displayed (indicated by the red display).
If there is not a corresponding data point in the current baseline, then the file
will be interpolated to provide the correction. The correction applied to each
point is dependent on the selected baseline type in the Baseline tab.
A baseline cannot be applied to a sample where the abscissa range of the sample
exceeds that of the baseline. If you change your abscissa range to one outside
that of the baseline, the Cary will display an error message. Also the red text in
the ordinate display which indicates that baseline correction mode is activated
will disappear.
For reflection measurements using the aperture kit, if the beam spot overfills the
aperture, you can correct for this “stray light” by performing a Zero/baseline
Correction. Normally, the 0%TBaseline scan is run by blocking the beam before
it enters the integrating sphere, which accounts for electronic noise. In this case,
do not block the beam, but instead remove the reflectance port cap to account
for the light reflecting on the edges of the aperture (the remainder of the light
should pass through the integrating sphere and not be detected).
Performing a Zero/Baseline Correction:
Select this option to apply a 100%T
baseline correction (100%TBaseline) and a zero-line correction (0%TBaseline)
to the sample scan (S). This correction is performed with the raw transmission
data and is thus:
(
𝑆
−
(
0%
𝑇𝐵𝑎𝑠𝑒𝑙𝑖𝑛𝑒
)
)
(
100%
𝑇𝐵𝑎𝑠𝑒𝑙𝑖𝑛𝑒
−
0%
𝑇𝐵𝑎𝑠𝑒𝑙𝑖𝑛𝑒
)
With this option, the Cary will prompt you to perform a 100%TBaseline first,
followed by a 0%TBaseline when you perform a baseline collection.
This baseline option corrects for any inherent variations in the electronic zero
line of the instrument. You should use this baseline option if your samples have
areas of very low transmission (high absorbance) as any variations in the
