Waters ACQUITY UPC2, Overview And Maintenance Manual, Page: 10 / 84

6
Flow cell operating principles
The Waters TaperSlit™ flow cell used in the detector renders the detector
baseline essentially insensitive 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. The
Waters TaperSlit flow cell, so-called because of the shape of the flow cell exit
face, matches the shape of the spectrograph slit. Compared with a
conventional flow cell with a cylindrical shape, the detector achieves higher
light throughput for a given spectral resolution with the TaperSlit cell design.
Comparison of flow cell characteristics:
Resolving spectral data
Together with photodiode spacing, the detector’s 50- μ m-wide slit determines
the intensity and bandwidth of the light that strikes the photodiode array.
Variations in intensity and bandwidth provide the means to distinguish
among similar spectra.
Window
Window
UV light
Conventional flow cell:
TaperSlit analytical flow cell:
Window
Lens
UV light