Agilent Technologies 1220 Infinity II LC User Manual page 122

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Detector Description
Agilent 1220 Infinity II LC Diode Array Detector (DAD)
Cell Support The cell support window assembly separates the holmium filter area from the
Window flow cell area.
Flow Cell The optical unit has a flow cell compartment for easy access to flow cells. A
Compartment variety of optional flow cells can be inserted using the same quick, simple
mounting system. The flow cell can be removed to check the optical and
electronic performance of the detector without having influences from the
flow cell.
Spectrograph
The spectrograph material is ceramic to reduce thermal effects to a minimum.
The spectrograph consists of the spectrograph lens, the variable entrance slit,
the grating and the photodiode array with front-end electronics. The
spectrograph lens refocuses the light beam after it has passed through the flow
cell. The sampling interval of the diode array is < 1 nm over the wavelength
range 190 – 950 nm. Depending on the wavelength this varies from 1.0 to 1.25
diodes per nanometer (for example a diode every 0.8 to 1 nm).
For a small wavelength range, the small non-linearity could be neglected. With
the wavelength range from 190 – 950 nm a new approach is required to
achieve wavelength accuracy over the full range. Each spectrograph is
calibrated individually. The calibration data is stored in the spectrograph on
an EEPROM. Based on these data, the built-in processors calculate absorbance
data with linear intervals (1.0, 2.0, ...) between data points. This results in an
excellent wavelength accuracy and instrument-to-instrument reproducibility.
Variable Entrance
The micro-slit system makes use of the mechanical properties of silicon
Slit System
combined with the precise structuring capabilities of bulk micro-machining. It
combines the required optical functions — slit and shutter — in a simple and
compact component. The slit width is directly controlled by the
micro-processor of the instrument and can be set as method parameter.
Grating
The combination of dispersion and spectral imaging is accomplished by using
a concave holographic grating. The grating separates the light beam into all its
component wavelengths and reflects the light onto the photodiode array.
Diode Array
The diode array is a series of 1024 individual photodiodes and control circuits
located on a ceramic carrier. With a wavelength range from 190 – 950 nm the
sampling interval is < 1 nm.
122 1220 Infinity II LC System User Manual