PDA-100 Photodiode Array Detector
3-20
Doc. 031644-02 9/03
Reference Wavelength
The reference wavelength is the center wavelength of the reference intensity
determination. Absorbance is measured by comparing the reference intensity to
the sample intensity. Selecting a reference wavelength implies a reference mode
for each of the single wavelengths being collected.
There are two types of reference mode: “active” and “off.”
•
To select the active reference mode, enter a wavelength within the scanning
ability of the PDA-100. The selected wavelength will be used as the reference
wavelength. The reference intensity will vary over time, as signal intensity
changes.
For maximum compensation, select a reference wavelength from the same
lamp as the sample wavelength. For example, if the sample wavelength is
272 nm, you might select a reference wavelength of 325 nm; both
wavelengths are within the UV spectrum of the deuterium lamp (190 nm to
380 nm).
Active reference mode minimizes baseline drift and is ideal for gradient
analyses, where the baseline may shift. Active mode also helps compensate
for fluctuations in ambient temperature caused by air conditioning.
NOTE When active reference mode is selected, be sure to select
a reference wavelength and reference bandwidth in a
quiet area of the spectrum where little absorption
occurs.
•
To deselect the active reference mode, enter “Off” as the reference
wavelength. The intensity reading at the time of autozero will be used as the
reference wavelength.
Operating when the reference wavelength is off ensures the lowest baseline
noise when running an isocratic analysis in a laboratory with stable ambient
temperature. It also ensures that fluctuations in the reference intensity do not
cause additional noise.
