Agilent 1100 - Bubbles from MCGV to Active Inlet Value w/Hex

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I have an Agilent 1100 and I am noticing when I run hexane through channel "D" I am seeing loads of tiny bubbles coming from the MCGV to the AIV. I am not noticing this with other solvents I use - Methanol, Water, or IPA.

My degasser was down for a while as it gave the Red LED display indicating the degasser needed service. We felt confident that the micro-vacuum pump went out so we ordered another one and installed it. The Red LED no longer displays and I can hear the vacuum working periodically. Solvents through the other channels don't have the bubble issue I mentioned.

I was attempting to rejuvenate a Raptor ARC-18 column yesterday and was running hexane with no problems for about 45 minutes before I noticed the loads of bubbles coming from the MCGV to the AIV. I switched back to 100% IPA and did not notice the problem.

Does anyone have any insight as to why this happens?
If you have some flow restriction in the inlet line (partially plugged sinker, or a kinked tube) and your system is running a bit warm, you may be seeing formation of vapor bubbles.
-- Tom Jupille
LC Resources / Separation Science Associates
+ 1 (925) 297-5374
In general, just replacing a worn out or damaged vacuum pump w/o first diagnosing the exact problem that caused the degasser to fail is a bad idea. Often, the replacement pump is installed back into a contaminated or damaged system, resulting in decreased lifetime of the pump and continued contamination throughout the system. Use of hexane can contribute to this. *A damaged degasser can lead to direct contamination of your mobile phase (pervaporation and condensation often occur and this results in the vapors and liquids inside picking up the internal contaminates, then reintroducing them back into the system).

    The most common reason for bubbles to appear going out of the multichannel gradient valve is from a loose low pressure fitting upstream. Usually a loose fitting exiting or entering the degasser will cause it.

If you are using a G1379-series of degasser, then it is possible that you may have damaged one of the vacuum chambers (very easy to do on that specific model). The damaged channel may have caused the pump to fail. If the chamber is damaged, it may show a restriction or may introduce air into the system. The G1322A degasser usually can handle hexane w/o any issues, but not the G1379A or G1379B (or any of the newer models).

I should point out that it is also possible the degasser is not the source of the bubbles, though it should be properly checked and serviced. Additionally, you should switch hexane to a different channel (from D to B) to see if the problem re-appears using a different VALVE position and also a different degasser CHANNEL.

If the seal inside the proportioning valve has dried out (and it will if you run hexane), all you need to do is connect that channel to a bottle of pure IPA and run it to waste at 0.5 mL/min for an hour or two. That will re-hydrate the solenoid seal inside the valve. Next, switch it on/off (50/50 cycle time) using two bottles of IPA so the valve switches between two positions (i.e. Channel C and D) for 20 minutes. After that, go ahead and run hexane again and see if the performance improves.
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