Agilent InfinityLab LC Series RID User Manual
20
1
Introduction to the Refractive Index Detector
Flow Path
Flow Path
The column eluent enters the optical unit through the in port and passes through
a heat exchanger. The combination of the heat exchanger and control of the
optical unit temperature in the range of 5 °C above ambient to 55 °CC minimizes
changes in refractive index due to temperature variations. The eluent flows
through the sample cell and via the same heat exchanger to the purge valve. With
the purge valve in the OFF position the eluent passes to the recycle valve. If the
recycle valve is also in the OFF/WASTE position the eluent will flow via the waste
port into the waste container.
If the recycle valve is in the ON/BOTTLE position the eluent will flow via the
recycle port back to the solvent bottle. The recycle valve can be manually set to
the ON or OFF position or the
Automatic recycling after analysis
mode can be
enabled. In this mode the recycle valve will automatically switch to the ON
position after each analysis has been completed and return to the OFF position
before the next analysis starts. Using this mode provides the benefits of
uninterrupted flow through the detector without the problems of excessive
solvent usage or the contamination of mobile phase with recycled sample
compounds.
If the purge valve is in the
on
position the eluent cannot pass immediately to the
recycle valve but will instead flow via a second heat exchanger through the
reference cell and then into the recycle valve. Periodically switching the purge
valve to the
on
position while only mobile phase is flowing will ensure that the
liquid in the reference cell is as similar as possible to the flowing solvent. The
purge valve can be manually set to the
on
position for a defined time or the
Automatic purge
mode can be enabled. In this mode the purge valve will
automatically switch to the ON position for a defined
purgetime
prior to the start
of each analysis. If a
purgetime
is set then a
waittime
must also be set to allow
the detector baseline to stabilize after the switching of the purge valve position.
After both the purgetime and waittime have been completed the analysis will
start. If the
Automatic zero before analysis
mode is enabled the detector output
will be set to zero immediately before the analysis begins.
The different flow paths depend on the status of the Purge Valve and Recycle
Valve.