Chromatography Forum

Hi,

Is there a general rule of thumb for how long the reference cell for an RI detector should be purged? Should it be purged with or without the LC column installed? At what flow rate should it be purged?

If anyone has experience with RI detectors, I would greatly appreciate it if you share your general detector purging steps!

First of all , I prefer purging without a column ; with a zero dead volume union connected ; for about 10 minutes.

Flushing the cell first with water , then with methanol will help to purge out the contaminants and the bubbles. Flush with water again ,if your mobile phase contains buffer , to prevent precipitation.

Up to 3 ml/min flow for purging can be used, but the detector outlet tubing must be taken into consideration , 0.5mm ID or larger tubing must be used , otherwise the backpressure may damage the flow cell , they are very fragile.

If your pump is a quat pump , connect only one channel to the pump inlet checkvalve directly, bypass the gradient valve.

If your pump is a quat pump , connect only one channel to the pump inlet checkvalve directly, bypass the gradient valve.

We always did this for both RI and conductivity detectors. Agilent has a little adapter, often mistaken for a fingertight nut !

If your pump is a quat pump , connect only one channel to the pump inlet checkvalve directly, bypass the gradient valve.

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If you do not want to do this, purge all your channels with mobile phase. IT is not exactly the same, but works very well if you do not want to bypass.

If your pump is a quat pump , connect only one channel to the pump inlet checkvalve directly, bypass the gradient valve.

We always did this for both RI and conductivity detectors. Agilent has a little adapter, often mistaken for a fingertight nut !

Can something similar be done on a Waters e2695?

Everyone’s tips on purging are spot on.
Couple of things to add . Always make sure your detector temperature is set to the temp your method states and your tubing from sample module to detector are as short as possible, this will help with equilibration and minimise drift, I also make sure I purge for 30 minutes plus and then let it flow through the detector for another 30 mins at least before starting analysis.
Also make sure you remove any non mobile phase solvent used for cleaning from both sides of the cell. RI is great but it is so susceptible to minor changes in temperature and flow rate.

Can something similar be done on a Waters e2695?

As 2695 is a low pressure side mixing 4 line system, I would be inclined to throw all 4 lines into the MP and prime all of them. Then leave them all in there and run 100% (line of your choice).