GE Analytical Instruments ©2006 13-10 DLM 14291 Rev. A
• While the peak is returning to baseline, load the next sample into the
syringe.
Preparation of Calibration Curve
After obtaining a clean water blank, inject the standards to prepare a
calibration curve. It is best to start with the most dilute standard and make
duplicate injections for each standard.
Analysis of Samples and Standards
Under normal operating conditions, the level of the VCl
3
reagent will be at the
top of the purge vessel and refluxing into the condenser. Remember the purge
vessel is HOT! Because of the extra volume of the gas bubbler and the slower
conversion of nitrate to nitric oxide, the peaks will appear about 30 seconds
after injection. For sera, plasma, or other sample containing high levels of
protein, the reagent will begin to foam as samples are injected. When the
foaming becomes severe, as indicated by foam exiting the condenser, replace
the reagent and clean the purge vessel. The reagent should be replaced before
the foaming reaches the NaOH. If the reagent foams into the gas bubbler, the
gas bubbler should be cleaned and fresh NaOH added to the bubbler. The
samples can also be deproteinized as described on page 11-10.
Serum and Plasma Samples
Serum and plasma samples are also quite viscous and can be difficult to draw
into microliter syringes and can clog the needles. Often these samples will also
contain suspended solids and a solid film over the top of the liquid. Injecting
these solids will result in poor repeatability for the measurement of nitrate.
Diluting serum or plasma samples 1:1 with nitrate-free water will make it
easier to analyze these samples and yield better reproducibility.
Samples containing protein will also change the viscosity of the VCl
3
/HCl
causing the level of the reagent to drop. Usually the level will return to near
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