AQ-00275-000, Rev. 3
20
rail at the transmittance port.
3. Set your instrument parameters as desired. Set the Y Mode parameter on the Setup
Dialog Box of your WinUV application to %T.
4. Perform an instrument baseline correction.
5. Load the sample or sample cuvette at the transmittance port. Initiate the scan and
record the measurement data.
6. The value displayed by the instrument is the sample transmittance. No data correction
is required.
For scattering samples, there are three primary types of transmittance measurement:
total
transmit-
tance,
diffuse transmittance,
and
regular transmittance.
For samples exhibiting a high degree of
scattering, the transmittance measurement procedure just described does not provide a measure-
ment of
total transmittance.
Instead, the result displayed by the instrument will be an instrument-
specific value that is known as the
regular transmittance factor.
For this particular accessory, how-
ever, the
regular transmittance factor
of a scattering sample closely approximates the
total trans-
mittance
of the sample.
Diffuse Transmittance Measurement Procedure
Using an integrating sphere reflectance accessory, the approximate
diffuse transmittance
of a given
test sample can be measured as follows:
1. Perform an instrument baseline correction.
2. Replace the standard positioned at the reflectance sample port with a light trap. This
light trap will capture, and exclude from measurement, the undiffused portion of the
flux transmitted by the sample.
3. Place the test sample in the transmittance sample holder. Perform a scan.
Determination of Regular Transmittance
The approximate
regular transmittance
of a given test sample can be determined by measuring its
total transmittance
and
diffuse transmittance,
as described above, and subtracting the latter from
the former:
where:
T
r
= regular transmittance,
T
t
= total transmittance, and
T
d
= diffuse transmittance.
T
r
= T
t
- T
d
Eq. 1