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 °C 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.
Purge Valve = OFF, Recycle Valve = OFF
This mode is used for flushing the complete detector inclusive the reference side of the flow cell.
Purge Valve = ON, Recycle Valve = OFF
This mode is used for saving solvent during periods where no sample is running through.
Purge Valve = OFF, Recycle Valve = ON
where
Capillaries (1) to (4) are part of the optical unit assembly. They are made of SST with an ID of 1.0 mm, except for (2), which has an ID of 0.2 mm. All other tubings (to and from the purge and the reference valve) are made of PTFE (available as ). |
where
Grey lines = flowing path Black lines = immobilized mobile phase | |
*The T-connection in the metal union block results in both sides of the flow cell (sample and reference) always being exposed to the same pressure |
where
Grey lines = flowing path Black lines = immobilized mobile phase | |
*The T-connection in the metal union block results in both sides of the flow cell (sample and reference) always being exposed to the same pressure |
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