Lightpipe Flowcell - Thermo Scientific Accela PDA Hardware Manual

LightPipe Flowcell

Thermo Scientific
The light focused on the inlet window of the LightPipe flowcell travels down the cell, is
partially absorbed by the sample flowing through the cell, and exits into the beam shaper. The
beam shaper is a fiber bundle. Its entrance aperture is circular to collect light from the
LightPipe flowcell. The other end of the bundle is arranged to produce a narrow "slit" of light
for the grating. The beam shaper transfers all the light to the grating for greater light
throughput than the mechanical slit used in conventional photodiode array detectors.
The folding mirror between the output of the beam shaper and the grating shortens the
optical bench, reducing the physical size of the detector. The grating disperses the light beam
onto the 512-element photodiode array (two of the diodes in this array are not used). Because
the spectrum of light falling on the array is 611 nm (190 to 800 nm, inclusive), the effective
spacing of the diodes is 611 nm / 510 = 1.2 nm. Firmware on the CPU PCB automatically
interpolates diode intervals to arrive at integer wavelengths.
The photodiode array is mounted on the Array Acquisition PCB, which also contains all the
analog detection circuitry. The PDA detector continuously scans the diode array at 20-, 40-,
or 80-Hz (user selectable), converts the light intensity at each diode into a 20-bit digital word,
and then stores these words in a dual-port Random Access Memory (RAM) on its CPU PCB.
The CPU reads the data, processes the data based on the user parameters, and sends the
processed data to the data system computer.
The Accela PDA Detector ships with a 10 mm or 50 mm LightPipe flowcell.
The internal bore of the 10 mm LightPipe flowcell is 10 mm long and has a volume of 2 μL.
The internal bore of the 50 mm LightPipe flowcell is 50 mm long and has a volume of 10 μL.
A special, low refractive index coating of the internal bore ensures a high optical throughput
and minimizes short-term noise.
The mobile phase enters the 10 mm LightPipe flowcell through a port in the bottom
of the LightPipe flowcell and exits through a port in the front of the LightPipe flowcell
(see Figure 3). Directing the flow upward helps prevent air bubble entrapment.
Figure 3. Schematic of 10 mm LightPipe flowcell
Inlet Outlet
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LightPipe Flowcell
Optical fibers
Accela PDA Detector Hardware Manual
Introduction
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