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Optimizing the detector
AZURA® Detector DAD 6.1L, DAD 2.1L, MWD 2.1L Instructions, V6700
6.3 Selecting the wavelength
Wavelength selection can influence the sensitivity, selectivity and linearity
of a measurement. The measurement wavelength can be selected within
the range from 190–1000 nm for the DAD 6.1L or 190–700 nm for the
DAD 2.1L and MWD 2.1L in 1 nm steps. The best wavelength for a given
measurement (signal wavelength) is that which fives the maximum ab-
sorption above the UV cutoff of the mobile phase. In cases where there
are multiple components with different absorbance maxima, a compro-
mise wavelength must be chosen where all components absorb.
In order to minimize baseline drift due to refractive index effects, a refe-
rence wavelength can be set in order to correct the baseline (see figure
22). The reference should be set in the same spectral region as the signal
wavelength (UV or Vis) but at a wavelength at which the analyte has no
absorbance.
By default, the reference wavelength 360 nm is activated (for channel 2).
This is a suitable value for most applications.
Fig. 27:
Comparison with and without baseline correction
When selecting the signal and reference wavelengths, the respective
bandwidths must also be selected (see the following section).
6.3.1 Bandwidth
The bandwidth defines the total number of wavelengths actually registe-
red by the photodiode when a specific wavelength is set. For example, a
wavelength set at 254 nm width a bandwidth of 4 nm results in average
absorption of 252–256 nm.
Fig. 28:
Bandwidth
Signal wavelength
Baseline correction /
reference wavelength
Default reference
wavelength
