Waters 2489, Overview And Maintenance Manual

Page: 19 / 150

June 11, 2015, 715004752 Rev. A
Page 19
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.
Figure 1–3: Comparison of flow cell characteristics
The standard analytical, inert, and LC/MS cells have a path length of 10 mm. The
semi-prep and microbore cell path length is 3 mm. The autopurification cell path
length is 1.0 mm. A variable path length flow cell (path length 0.15 to 3 mm) is also
available.
1.2.1.3 Selecting the appropriate sampling rate
A sufficient number of points must fall across a peak to define its shape. Thus, at very
low sampling rates, the definition between peaks is lost. The chromatography data
software uses the index of the data point closest to the end time, minus the index of
the data point closest to the start time, to calculate a value for each integrated peak
in the chromatogram.
Tip:
In Empower software, this value is called the Points Across Peak value, and it
appears in the Peaks table, at the bottom of the Review Main window. If the Points
Across Peak field is not visible, right-click anywhere in the table, and then click Table
Properties. Click the Columns tab, and then scroll down to find the Points Across Peak
field. Clear the check box, and then click OK.
UV light
UV light
Conventional cell
TaperSlit analytical cell
Window
Window
Window
Window