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Applications
These illustrations show basic sample injection techniques using Cheminert two
position valves. With rare exceptions, there is no difference between switching
valves and external volume sampling valves, so the same valve can be used for
either function.
The unique advantage of 8 and 10 port valves is that they reduce extra column
volume by combining sampling and switching functions in a single valve. This
minimizes expense, maintenance, service, and risk of leaks as compared to
multiple 6 port valve systems.
4
Port Internal Sample Injector
Microvolume Sample Injection
The internal sample (fixed volume)
flowpath is used when very small sample volumes are required. The sample
size is determined by a passage engraved on the valve rotor, allowing
precise, repeatable injections. In Position A, the sampleflows through
the sample passage while the mobile phase flows through to the column.
The third passage is inactive. In Position B,the sample passage is in
line with the column and the mobile phase injects the contents of the
sample passage into the column.The passage which was inactive in
Position A allows the sample to continue flowing without interruption.
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4
Port Internal Switching Valve
Detector Selection from Two Columns or
One Column and Auxiliary Carrier
This unique configuration allows
analysis of different parts of one analysis with two different detectors,
without splitting or multiple injections. For example, fixed gases can
be analyzed with a thermal conductivity detector, followed by the
analysis of a hydrocarbon fraction with a flame ionization detector.
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6 PORT
EXTERNAL SAMPLE INJECTOR
Sample Injection
With the valve in Position A, sample
flows through the external loop while the mobile phase flows directly
through to the column. When the valve is switched to Position B, the
sample contained in the sample loop and valve flow passage is displaced
by the mobile phase and is carried into the column.Note: Especially for
partial-filled loops, the flow direction of the mobile phase through the
loop should be opposite (backflush) to the flow direction during the
loading of the loop. |
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8 PORT
SAMPLING / SWITCHING
Loop Sampling
with Backflush to Detector
One valve functions as sampling and
backflush valve, simplifying operation and reducing cost. When
components
of interest are detected, the strongly retained components are
backflushed and removed from the column without temperature programming. |
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10
PORT SAMPLING / SWITCHING
Alternate Column Regeneration
When columns must be regenerated
following each analysis, this technique permits automation of the
process. While one column performs the analysis, the second column
undergoes regeneration by use of an auxiliary pump. Once the first
analysis is complete, the valve is switched and the regenerated column
is now ready for analytical use. |
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