GE Analytical Instruments ©2006 16-13 DLM 14291 Rev. A
Leaks in Purge System
Leaks can occur at the septum, the Swagelok connections to the purge vessel and
gas bubbler, at the Teflon sleeve of the gas bubbler and at the IFD filter. For
nitrate measurement, the best way to test for leaks is to see if the reagent will
vacuum distill (see Leak Check for Purge Vessel, page13-5). If the reagent does not
vacuum distill, there is a leak in the system.
Leaks at the Swagelok connections can occur if the connection is not tight, if the
ferrules are missing or not properly position (see Figure 11-2). Another problem is
glass in the reducing union of the fitting. If the end of the glass is broken, a tight
connection can still be achieved provided that the Teflon ferrules are installed
over the broken end and any glass is removed from inside the reducing union.
Another common location for leaks when using the gas bubbler is at the Teflon
sleeve. Make sure the connection for the bubbler is tight.
Leaks can also occur at the septum. Try replacing the septum to see if this solves
the problem.
Low Conversion for Nitrate
If the VCl
3
/HCl reagent is oxidized or the temperature of the water bath and purge
vessel is too low, the conversion of nitrate to NO will be slow causing reduced
sensitivity. Make sure the temperature of the water bath is set to 95 °C so that the
purge vessel will be at least 90 °C. One test for low temperature or depleted
reagents is to analyze a nitrite standard using the VCl
3
/HCl reagent. Since nitrite is
converted by reaction with acid at room temperature, higher response for nitrite
versus nitrate indicates a problem with the reagent or the water bath.
Poor Repeatability
All of the items listed (leaks, depleted reagents, etc.) above can also result in
poor repeatability for replicate injections. Other causes include syringe problems,
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