Chromatography Forum

Hi,
This is my first time posting in this forum, so I hope that this is an appropriate area for my question.

Essentially, I have a very old Dionex DX-120 IC that I have "inherited" at a new job. The IC used to work very well, and was primarily used for anion and cation analysis of water samples. Currently, the pressure is extremely high. I have tried to systematically isolate where the high pressure is coming from, and it looks like it is somewhere within the column switching valve. I replaced the old column switching valve with a new one. This slightly reduced the pressure, but not significantly. The pressure does not seem to be coming from the guard column or the analytical column.

I have had an extremely difficult time finding any information or suggestions regarding this situation, primarily because the instrument is so old. Apparently it has been a really good instrument and we would like to get it running again. We only ran three to four samples per week on it, so it's not like it makes sense to buy a brand new IC. Everything else on the instrument seems to be working well.

Thoughts or suggestions would be appreciated!

Thank you in advance,
Karin

You need to find where pressure builds up. Connections in the instrument are probably with PEEK tubing. If you find the culprit you may simply replace that tubing. You may as well try to unclogg it in the counter current flow. The column switching valve may be omitted if it is clogged and you can't fix it or replace.

When I worked with that model most of our pressure issues were related to the pump going into vapor lock. Try opening the purge valve on the pump and letting the pump work for a few minutes. That should get rid of any gas trapped in the pump.

If that doesn't work, try using a union to bypass certain areas of interest to help locate the cause of the pressure issue.

Hi Karin

Could you provide some numbers about the the actual pressure? And, did you checked the flow rate? The flow on the pump is set by a mechanical knob. It is absolutely important that you measure the flow gravimetrically (weight over time) and adjust if needed.
Here you can download the manual, just for the case you haven't: http://www.dionex.com/en-us/webdocs/4520-31183-03.pdf

I wish you success.
Best regards

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