GE Monitor UV-900, User Manual

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Reference information
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Monitor UV-900 User Manual 18-1120-05 Edition AF
A.2 Flow cell
The optical path length of the flow cell is 2 mm and 10 mm. The flow cell is made
of quartz with a titanium housing.
The unique design of the flow cell prevents the formation of distinct interfaces
between eluent components with different refractive indices and eliminates
the negative influence these would cause. The precision of monitoring is
enhanced by the construction of the flow cell, which ensures total reflectance
of light. This maintains a high intensity of light to the detector. The long path
length combined with a small cell volume increases sensitivity.
A.3 Monitor principle
A Xenon flash lamp gives a high intensity, continuous spectrum throughout the
range 160–2000 nm. The light enters a monochromator which includes a
condensing system, blocking filter, entrance slit and a concave aberration-
corrected holographic grating. Monochromatic light from the grating is
directed to an optical fibre. The grating is turned by a stepping motor for
wavelength selection between 190–700 nm, in steps of 1 nm. Up to 3
wavelengths can be monitored simultaneously.
For wavelengths between 360–700 nm, a blocking filter is moved into the light
path to filter out unwanted light, of a half wavelength from the second order
spectrum, before entering the monochromator.
The light from the monochromator to the flow cell and from the cell to the
detector electronics is guided by optical fibres which focus its full intensity on
the liquid flow path, maximising the sensitivity of the monitoring. Before
entering the flow cell, the monochromatic light is split in a beam splitter, with
50% of the light passing through the sample fibre (S) and the flow cell, and 50%
being directed through the reference fibre (R). Two photodiodes with identical
characteristics monitor the intensities of the measuring and reference beams.