Agilent Technologies 8453 Operator's Manual page 153

Theory of Operation
Firmware Description
Intensity Run Buffer
ChemStation Software
Intensity spectra with their variances are intermediately stored in the
intensity run buffer if the acquisition of spectra is faster than the processing
and data transfer to the ChemStation.
Handheld Controller Software
The intensity run buffer is not used by the Agilent 8453E UV-visible
spectroscopy system, because measuring time resolved intensity spectra is
not supported by the handheld controller software.
Stray-Light Correction
Two intensity spectra are used for stray-light correction, one is measured
with the stray-light filter in the light path and one without. Both spectra are
combined to form one stray light corrected, temperature corrected, gain
corrected, dark current corrected intensity spectrum.
Absorbance Calculation
To form an absorbance spectrum, the stray-light corrected intensity spectrum
of the reference is divided by the stray-light corrected intensity spectrum of
the sample and the logarithm is calculated, see "Optical System Overview" on
page 19.
Wavelength Axis Linearization, Deuterium Line Data,
Wavelength Calibration Table
Photodiodes are located on the array to give a sampling interval of nominal
0.9 nm over the whole wavelength range in the UV wavelength range. In the
visible and short wave near infrared wavelength ranges the sampling interval
is slightly higher. To correct for this optical non-linearity and to convert from
discrete diode distances to a continous, linear scale, an interpolation
algorithm is applied. This algorithm uses a wavelength calibration table and
actual wavelength data, derived from the deuterium emission lines at 486 nm
and 656 nm.
• Wavelength calibration is done for each individual spectrograph during the
production process using emission lines of a mercury lamp, deuterium
lamp, and a zinc-argon lamp. The individual calibration coefficients are
47