Agilent InfinityLab LC Series Diode Array Detectors User Manual
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5
Optimizing the Detector
Optimizing the Detector Regarding to the System
How to Achieve Higher Sensitivity
The detector has a number of parameters that are used to optimize
performance. The following sections describe how the detector parameters
affect performance characteristics:
•
Flow cell affects sensitivity,
•
Wavelength and bandwidth affect sensitivity, selectivity and linearity,
•
Slit width affects sensitivity, spectral resolution and linearity,
•
Peak width affects sensitivity and resolution.
Flow Cell
The Max-Light cartridge flow cell has a standard 10 mm path length and is
optimized for minimal volume and dispersion (
volume 1.0 µL). It has high light
transmission minimizing noise to reduce noise due to the optofluidic waveguide.
It is suitable for use with a wide range of analytical columns from short
narrow-bore columns to long standard diameter (4.6 mm) columns. Generally the
peak dispersion volume (calculated from peak width x flow rate) should be
greater than about 2 µL for this cell (for example 0.02 min x 200 µL/min = 4 µL).
The Max-Light high sensitivity cell has a path length of 60 mm and this will give
between three and five times increase in signal-to-noise values depending on the
application conditions. The dispersion volume is fractionally increased compared
to the standard cell.
Wavelength and Bandwidth
The detector measures absorbance simultaneously at wavelengths from 190 nm
to 640 nm using diode-array detection. A UV-lamp provides good sensitivity over
the whole wavelength range. The diode-array detector (DAD) can simultaneously
compute and send to the data system up to eight chromatographic signals and
the full-range spectra at every time point.
A UV chromatogram or signal is a plot of absorbance data versus time and is
defined by its wavelength and bandwidth.
•
The wavelength indicates the center of the detection band.
•
The bandwidth defines the wavelength range over which the absorbance
values are averaged to give the result at each time point.
For example, a signal at wavelength 250 nm with a bandwidth of 16 nm will be an
average of the absorbance data from 242 nm to 258 nm. Additionally, a reference
wavelength and reference bandwidth can be defined for each signal. The average
