Sample And Reference Wavelength And Bandwidth - Agilent Technologies 1260 User Manual

Sample and Reference Wavelength and Bandwidth

The detector measures absorbance simultaneously at wavelengths from 190 to
950 nm. Two lamps provide good sensitivity over the whole wavelength range.
The deuterium discharge lamp provides the energy for the UV range (190 to
400 nm) and the tungsten lamp emits light from 400 to 950 nm for the visible
and short wave near infrared.
If you know little about the analytes in your sample, use both lamps and store
all spectra over the full wavelength range. This provides full information but
fills up your disk space rather quickly. Spectra can be used to check a peak's
purity and identity. Spectral information is also useful to optimize wavelength
settings for your chromatographic signal.
The detector can compute and store at run time up to 8 signals with these
properties:
• sample wavelength, the center of a wavelength band with the width of
• reference wavelength, the center of a wavelength band with the width of
The signals comprises a series of data points over time, with the average
absorbance in the sample wavelength band minus the average absorbance of
the reference wavelength band.
Signal A in the detector default method is set to sample 250,100, reference
360,100, that is, the average absorbance from 200 – 300 nm minus the average
absorbance from 300 – 400 nm. As all analytes show higher absorbance at
200 – 300 nm than at 300 – 400 nm, this signal will show you virtually every
compound which can be detected by UV absorbance.
Many compounds show absorbance bands in the spectrum.
page 124 shows the spectrum of anisic acid as an example.
To optimize for lowest possible detectable concentrations of anisic acid, set
the sample wavelength to the peak of the absorbance band (that is, 252 nm)
and the sample bandwidth to the width of the absorbance band (that is,
30 nm). A reference of 360,100 is adequate. Anisic acid does not absorb in this
range.
If you work with high concentrations, you may get better linearity above
1.5 AU by setting the sample wavelength to a valley in the spectrum, like
225 nm for anisic acid.
Agilent 1260 Infinity DAD and MWD User Manual
Optimizing for Sensitivity, Selectivity, Linearity and Dispersion
sample bandwidth (BW), and optionally
reference bandwidth.
How to optimize the Detector
Figure 53
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