Transmission, Relative irradiance, Concentration – Ocean Optics CHEM2000 User Manual
Page 13
2: Using OOIChem Software
Transmission
Selecting this mode switches the spectral window into Transmission Mode. This is also the spectral
processing mode used for Reflection spectroscopy, as the math necessary to compute reflection is
identical to transmission. Before this can occur, both a dark and reference scan must be stored in Scope
Mode (see
). The transmission of a solution is calculated by the following equation:
S
λ
- D
λ
%T
λ
=
R
λ
- D
λ
x 100%
Where:
S = Sample intensity at wavelength
λ
D = Dark intensity at wavelength
λ
R = Reference intensity at wavelength
λ
Relative Irradiance
Selecting this mode switches the spectral window into Relative Irradiance Mode. The reference spectrum
must be made in Scope Mode with a blackbody of known color temperature. (Maxwell users cannot make
relative irradiance measurements because the light source that comes with the system is not a blackbody
source with a known color temperature. Additional hardware must be purchased.) A dark spectrum is
usually obtained by preventing light from entering the fiber that connects to the spectrometer (see
). Relative irradiance spectra are a measure of the intensity of a light source relative
to a reference emission source. Relative irradiance is calculated by the following equation:
S
(
λ
- D
λ
I
λ
=B
λ
R
λ
- D
λ
)
Where:
B = Relative energy of the reference calculated from the color temperature (in Kelvin)
S = Sample intensity at wavelength
λ
D = Dark intensity at wavelength
λ
R = Reference intensity at wavelength
λ
Concentration
Concentration is the amount of a specified substance in a solution. Graphs of absorbance vs.
concentration are known as Beer’s Law plots. These are calculated by first measuring the light that is
absorbed from a series of solutions with different known concentrations. The length of the sample -- such
as the path length of our cuvette holder – and the wavelength chosen for monitoring the amount of light
absorbed, are constants. Then a linear plot derived from the scans of these standard solutions with known
concentrations is obtained. The plot is then used to determine the unknown concentrations of solutions.
(see
105-00000-CHM-02-0405
PRELIMINARY DRAFT
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