Waters 2489, Operator'S Manual

Page: 115 / 234

Scanning spectra 3-47
When you select a zero scan:
• The detector displays three additional screens, labeled 2 of 4, 3 of 4, and
4 of 4.
• You can change all parameters on these screens, including starting and
ending wavelength, and the pace parameter.
When you select a sample scan:
• The detector displays two additional screens labeled 2 of 3 and 3 of 3 (see
the figure on
page 3-51 ).
• You cannot change the starting and ending wavelength parameters or
the pace parameter.
When you run the zero scan, you set up the starting and ending wavelengths,
pace, tickmarks, and sensitivity for both the zero scan and subsequent sample
scans. You should try to run sample scans within 15 minutes of the baseline
zero scan.
The most recent zero scan performed or retrieved remains current until you
perform or retrieve another scan. The zero scan should be appropriate for the
subsequent sample scans you perform. The sample scan uses the starting and
ending wavelengths and pace from the most recent zero scan. Only when these
parameters are identical for both the zero and sample scans can the zero scan
be subtracted.
You use the SCAN key (Shift Chart Mark) to run a new zero or sample scan,
store, review, subtract and review, and replay stored or existing scans.
During a sample scan, data are charted out the detector analog channel A
using the specified AUFS setting. At the same time, sample energy at 150
nA/V is charted out over channel B.
During a zero scan, the data are charted out the detector analog channel A. At
the same time, reference energy at 150 nA/V is charted out channel A at the
AU specified on channel A.