GE MOA 280i, Руководство по эксплуатации и обслуживанию

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GE Analytical Instruments ©2006
12-12
DLM 14291 Rev. A
Sample Analysis
The procedure for sample analysis is the same as described above. If the samples
contain protein, the reducing agent will begin to foam as more protein is added to
the vessel. The anti-foaming agent will reduce the amount of foaming; however,
after injecting a large number of samples, foaming from the protein will begin to
reach the condenser of the purge vessel. Once the foaming becomes severe, or if
there is liquid in the outlet of the purge vessel (the line connected to the IFD
filter), drain the reducing agent, clean the purge vessel and prepare fresh
reducing agent. While running samples containing protein, observe the IFD filter to
make sure that liquid is not collecting in the filter. The filter will initially block
the liquid from getting into the NOA, but since the filter is under vacuum
eventually the liquid will pass through the filter into the reaction chamber. If
there is liquid in the filter, stop the purge vessel, clean and replace the reducing
agent and clean the filter as described below. (see page 12-16).
Foaming problems can also be minimized by keeping the injection volumes small.
The amount of protein injected into the purge vessel will be the same for one
injection of 100 µL or 100 injections of 1µL, thus more samples can be analyzed
before replacing the reducing agent by keeping the injection volumes small. The
best injection volume will depend on the concentration of nitrite being measured
and the amount of protein in the samples.
Some culture media contain high levels of protein and should be deproteinized
before injection into the purge vessel. For example, media with 10% BSA or fetal
calf serum will start to foam after only a few injections. To determine if the
media has too much protein for direct analysis, inject several different sample
sizes (for example, 1 µL, 10 µL and 100 µL) and observe how much foaming occurs
in the purge vessel. Deproteinization procedures are described in Chapter 11 (page
11-10).
Background Nitrite