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Introduction
LightPipe Flow Cell
Thermo Scientific
Surveyor PDA Plus Detector Hardware Manual
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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 diode array is continuously scanned at a 20-Hz rate, the light
intensity at each diode is converted into a 20-bit digital word, and these words are stored in a
dual-port Random Access Memory (RAM) on the CPU PCB. As the data points are stored
through one RAM port, the CPU reads the data it needs (based on user parameters entered
through the software) through the other RAM port, processes the data, and sends it to the
computer.
LightPipe Flow Cell
The Surveyor PDA Plus Detector ships with a 10-mm LightPipe flow cell. Thermo Fisher
Scientific also offers an optional 50 mm LightPipe flow cell.
The internal bore of the 50-mm LightPipe flow cell is 50 mm long and has a volume of
10
L. The internal bore of the 10-mm LightPipe flow cell is 10 mm long and has a volume
of 2
L. A special low refractive index coating of the internal bore ensures a high optical
throughput and minimizes short-term noise.
Mobile phase enters the 50 mm LightPipe flow cell through a port in the bottom of the flow
cell and exits through a port in the top of the flow cell as shown in
. Directing the
flow from the bottom to the top of the flow cell helps prevent the entrapment of air bubbles.
Figure 3.
Schematic of 50 mm LightPipe flow cell
Alignment slot
Outlet
Inlet
