Low Results On X10 Range; Erratically High Results - Micromeritics FlowSorb III 2305 Operator's Manual

Troubleshooting
4
5
6
7

Low Results On X10 Range

The X10 range (10 times increase in detector sensitivity) is provided when analyz-
ing samples that produce less than a 10% enrichment for nitrogen in the gas
stream. The detector signal is truncated when this 10% limit is exceeded which re-
sults in a lowered surface area value. A high-pitched audio tone is sounded if
the possibility of misleading results occurs.

Erratically High Results

Failure to reset the surface area display to zero after passage of the air peak is
often responsible for an apparently high result.
Air peaks or peaks due to other gases passing through the Long path may be for-
gotten due to their extended transit time and add to a subsequent surface area.
You should be particularly aware of this possibility when a Short path adsorption
followed by a Long path desorption is employed to save time.
Adding liquid nitrogen to the Cold Trap while a surface area result is accumulat-
ing can cause gas flow to decrease or even to stop momentarily. This will extend
the time of gas passage and violate the assumption of constant flow rate upon
which the surface area accumulation technique is based. The result is a somewhat
greater surface area value than would otherwise have been achieved. The liquid
nitrogen supply should only be replenished between tests or while awaiting air
peak passage.
4-2
Incompletely degassed samples cause detector drift and offset because
contaminants can still be flushed from the sample at room temperature.
Such drift and offset will cease once the sample is immersed in liquid
nitrogen.
Leaks caused by a worn septum; always use a good septum. Replace
the septum periodically; after approximately 100 injections when using
the 1-mL syringe and approximately 20 injections when using the 10-
mL syringe. Refer to Replacing the Septum in this chapter.
Leaks caused by loose plumbing. If it becomes necessary to tighten
plumbing connections, be sure not to overtighten them. Overtightening
can easily damage small copper tubing.
Leaks caused by missing or damaged sample tube O-rings. Discard
cracked or chipped sample tubes to avoid leaks and avoid damaging
the O-rings. Always use clean, undamaged O-rings which have a light
film of vacuum grease applied.
FlowSorb III
Aug 00