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by any part of the VASH or sample at the incidence angle you require. When making angle adjust-
ments to the device, see that the sample surface is pointing away from the reference beam entrance
port.
The 0° location on both clip style and jaw style sample holders configures the sample for normal
incidence where the reflecting surface is perpendicular to the path of the sample beam. When
using a reference standard, the reflecting surface of the standard should be the same angle of inci-
dence as the sample.
Reflectance Measurements Using a Center Mount Sample Holder
When taking reflectance measurements, a diffuse reflectance standard typically is used to deter-
mine relative reflectance measurements of your samples. If your diffuse reflectance standard is cal-
ibrated, the reflectance factors are provided in the calibration documentation accompanying your
accessory. If your reflectance standard is uncalibrated, you can use the reflectance values given in
Appendix B.
The purpose of the variable angle sample holder is to compare the diffuse reflectance of the sample
at different angles of incidence. The center mount configuration can produce either relative or
absolute reflectance results and certain angles, depending on the design of the sample holder. The
reflectance standards at Labsphere, however, are calibrated at 8
°.
Before using a center mount sample holder, you will need to realign the transfer optics in the
accessory.
1. Load the sample into the sample holder, making sure it is properly centered and
secured to the holding device.
2. Load the sample holder into the center mount port and set the desired angle of inci-
dence on the attached dial.
3. Darken the room and set the instrument for white light operation.
4. Viewing the sample surface through the reflectance port, check that the beam strikes
the center and does not overfill the sample surface. This step will be more difficult at
greater angles of incidence. If the beam is off center, readjust the sample beam optics
to achieve the correct alignment.
5. Remove the sample holder and remove the sample. If your sample holder is the jaw
type, install a diffuse reflectance standard into the device. If your sample holder is the
clip type, the baseline scan is measured with the empty sample holder. If your sample
holder is the Edwards style, take the baseline using the back side of the clamping
device.
6. Load the sample holder into the center mount port and set your instrument parameters
as desired. Set the Y Mode parameter on the Setup Dialog Box of your WinUV appli-
cation to %R.
7. Perform the baseline correction scan.
8. When the baseline scan is complete, remove the sample holder and load the sample
into the sample holder clamping device. For the jaw style device, you must eliminate
the transmitted component of the sample beam. This can be accomplished by backing
the sample with a piece of black felt cloth.
9. Run the scan and record your measurement data.
10. If your sample holder is the jaw style, multiply the values recorded in the resulting