Waters 2489, Operator'S Manual

Page: 22 / 234

1-6 Theory and Principles of Operation
4. The preamplifier board integrates and digitizes the currents from the
photodiodes for processing by the signal processing electronics and
output to a computer, chart recorder, or integrator.
Waters TaperSlit Flow Cell
The Waters TaperSlit Flow Cell used in this detector renders the detector
baseline less sensitive to changes in mobile phase refractive index (RI). RI
changes occur during gradient separations or result from temperature or
pump-induced pressure fluctuations.
To achieve RI immunity, a combination of a spherical mirror, a lens at the
entrance of the flow cell, and a taper to the internal bore of the flow cell
prevents light rays from striking the internal walls of the flow cell. An
additional feature of the TaperSlit flow cell and the reason for its name is the
shape of the flow cell entrance, which matches the shape of the entrance slit.
The detector achieves higher light throughput for a given spectral resolution
via the TaperSlit cell design, compared to a conventional flow cell with a
circular entrance.
As shown in the figure below, in a conventional cell, light bends and hits the
wall of the flow cell. Four beams go in, but only two come out. In the Waters
TaperSlit Analytical Cell, the combination of the lens and TaperSlit bore
geometry prevents light from hitting the cell walls. Four beams go in, and four
beams come out.