Optimizing Spectral Acquisition - Agilent Technologies InfinityLab LC Series User Manual

5 Optimizing the Detector
Optimizing for Sensitivity, Selectivity, Linearity and Dispersion
Furthermore, the absorbance is no longer strictly linear with concentration for
wavelengths at a steep slope of a compound's spectrum.
Substances with fine structures and steep slopes like benzene are very rare.
In most cases the width of absorbance bands in the spectrum is more like 30 nm
as with anisic acid (
In most situations, a slit width of 4 nm will give the best results.
Use a narrow slit (1 or 2 nm) if you want to identify compounds with fine spectral
structures or if you need to quantify at high concentrations (> 1000 mAU) with a
wavelength at the slope of the spectrum. Signals with a wide bandwidth can be
used to reduce baseline noise. Because (digital) bandwidth is computed as
average of absorbance, there is no impact on linearity.
Use a wide (8 nm) slit when your sample contains very small concentrations.
Always use signals with bandwidth at least as wide as the slit width.

Optimizing Spectral Acquisition

Storage of all spectra consumes a lot of disk space. It is very useful to have all
spectra available during optimization of a method or when analyzing unique
samples. However when running many samples of the same type, the large size
of data files with all spectra may become a burden. The detector provides
functions to reduce the amount of data, yet retaining the relevant spectral
information.
Range
Only the wavelength range where the compounds in your sample absorb
contains information that is useful for purity checks and library searches.
Reducing the spectrum storage range saves disk space.
Step
Most substances have broad absorbance bands. Display of spectra, peak purity
and library search works best if a spectrum contains 5 to 10 data points per
width of the absorbance bands. For anisic acid (the example used before) a step
of 4 nm would be sufficient. However a step of 2 nm gives a more optimal
display of the spectrum.
Agilent InfinityLab LC Series Diode Array Detectors User Manual
Figure 23 on page 88).
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