GE MOA 280i, Operation And Maintenance Manual

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GE Analytical Instruments ©2006
12-8
DLM 14291 Rev. A
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Figure 12-2: Typical Peaks
from Injections of Water
The 100 mM nitrite standard is stable for several weeks, if stored in an air tight
container, refrigerated (4 °C or lower), and not exposed to light. The lifetime can
be extended by storing the solution headspace free. The dilute standards are not
stable and should be prepared fresh each day.
After preparing the dilute standard solutions, the calibration curve is constructed
by injection of the standards into the Purge Vessel, and measurement of the peak
area for each standard. To prepare a concentration-based calibration curve, inject
the same volume for all of the standards and samples. For amount-based
calibrations, different volumes can be injected, but the volume must be included
in the sample name. For a 10 µL syringe, injection of 5 µL is a good injection
volume and will allow construction of calibration curves down to ~0.2 µM. For best
results using the 10 µL syringes, injection volumes should be between 2 to 8 µL.
For measurement of lower concentrations, injection of 10 to 100 µL will be
required using larger syringes. For a 100 µL injection, calibration curves down to
10 nM can be constructed.
Water Blanks
Before analyzing the standards, check the nitrite levels in the water used to
prepare the standards by injecting water from the sample tube created during
standard preparation. Inject the water sample into the purge vessel, being sure
that the liquid is injected into the reducing agent. If the solution does not contact
the reducing agent or contacts the glass on the side of the purge vessel, nitrite
will not be rapidly converted, resulting in a broad peak.
Figure 12-2 shows a typical result from several
injections of water. With freshly prepared
iodide/acid reducing agent, the first injection
of water results in a relatively large peak,
presumably due to nitrite in the reagents. The
peak size decreases with additional water