Column overload in a plasma chromatograph/mass spectrometer can result in several hours of purging being required in order to establish a clean background spectrum. The apparatus shown above can be used to prevent column overload.
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Prevention Of Column Overload In A Plasma Chromatograph/Mass
Spectrometer
Column overload in a plasma chromatograph/mass spectrometer can result
in several hours of purging being required in order to establish a clean
background spectrum. The apparatus shown above can be used to prevent
column overload.
A normally open, electrically actuated diverter valve allows about 90% of the
carrier gas to flow through the heating block into the sample chamber in the
sample oven. The remaining 10% of the carrier gas passes through a flow
restrictor in a bypass line, and joins the carrier gas as it again flows through the
gas heating block on its way back to the plasma tube. The small gas flow in the
bypass line continually sweeps out the bypass line and prevents sample
contamination in it by backflow or diffusion. When the diverter valve is closed,
the full carrier gas flow is through the bypass line, and none of the gas in the
sampling chamber is swept into the plasma tube.
If the sample concentration becomes too high (as evidenced by the
simultaneous disappearance of the three reactive ion peaks in the
chromatogram), the diverter valve can be closed to abort the run and prevent
column overload. In an automated system, the three reactive ion peaks can be
continuously monitored and can be used to trigger a circuit to cause the diverter
valve to close when the incipient overload condition is detected.
This apparatus can also be used to advantage when dealing with very small
s...
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