Thermo Scientific Vanquish VH-D10 Operating Manual page 103

Slit Width
Diode Array Detectors (VH-D10)
Operating Manual
Note the following:
• The averaging always takes place symmetrically to the selected
wavelength.
• When performing a detection near the edge of the spectral range
If the bandwidth setting results in an averaging asymmetrically to
the selected wavelength, the device will correct the setting.
Example: If you perform a detection at a wavelength of 195 nm with
a bandwidth of 20 nm, the photodiode bunching is set to 190 to
200 nm, i.e. the largest possible symmetrical range around the
detection wavelength. As a result, the bandwidth is changed to
10 nm. This is done to avoid a wavelength shift as would be the case
with an asymmetrical averaging.
The following table serves as guidance for selecting the bandwidth
based on the spectral features of the analyte to be detected:
Spectral Features
Samples with extremely fine
spectral features, such as
benzene, and very high
absorptions.
Samples for "normal" analysis
with fine spectral features,
such as caffeine.
Samples with broad spectral
features.
A narrow slit width results in a smaller optical bandwidth and provides a
better optical resolution (the ability of the device to distinguish between
single wavelengths) which is required for analytes with fine spectral
structures (such as benzene).
Set a value for the slit width that it is not smaller than the smallest value
of all bandwidths and bunch widths used for measurement. If the
smallest value is greater than 8 nm, select a slit width of 8 nm.
The setting of the slit width affects all signal channels and the 3D field.
Bandwidth Effect
< 4 nm May increase baseline noise.
4 nm – 8 nm Reasonable compromise between
low baseline noise, good linearity
and low cross-sensitivity
> 8 nm Most suitable for low noise. A
reduced linearity and increased
cross-sensitivity may occur.
6 • Operation
Page 103