June 11, 2015, 715004752 Rev. A
Page 78
3.3 Scanning spectra
Note:
If your flow cell does not require a cuvette, you can obtain an analytical flow
cell to perform the spectral scanning. See the Waters Quality Parts Locator on the
Services and Support page of the Waters’ Web site.
The detector must make two scans to produce an absorbance spectrum, as shown in
the table below.
The detector can measure the spectrum of a sample using the cuvette or the flow cell.
and
Requirement:
When using the cuvette, if the contents of the flow cell change, you
must rerun the zero scan.
3.3.1 Before you begin
Before you run a spectrum scan, specify values for the following parameters:
•
λ
1 – Starting wavelength. Scanning begins at this wavelength.
•
λ
2 – Ending wavelength. Scanning ends at this wavelength.
•
Pace – Rate of scanning, in nanometers/min. Determines how fast the scan is
output and data are acquired. The scan data are acquired at the highest
possible resolution for the specified pace. Specifying a very high pace reduces
resolution.
The figure below shows two scans of anthracene, one overlaying the other. At a
pace of 1000 nm/min, the overlaid scan (dotted line) shows a reduced number
of points scanned, lowering the resolution relative to the original scan, done at a
pace of 100 nm/min.
Table 3–4:
Absorbance spectrum scans
Scan
Description
Zero scan
A reference scan that characterizes the absorbance
spectrum of the solvent in the cuvette or the flow cell.
Sample scan
An absorbance scan of the analyte in solvent (after
subtracting out the zero scan of the solvent) to provide
the actual spectrum of the sample.
Pace and sampling resolution examples
Pace (nm/min)
Sampling resolution (nm)
100 and less
0.5
200
1.0
400
2.0
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