Hydrogen safety shutdown on Agilent 7890

[AnaChem1983]

Hi all,

I've been experiencing problems with a GC shutting down recently as it thinks there's a leak at the inlet. I came in to find it alarming with hydrogen safety shutdown on the display. Understandable given we use hydrogen as the carrier gas and it thinks there's a leak.

Initially I went through the usual things to resolve this e.g. replacing septum, making sure fittings were tight enough and upon resetting the GC the initial settings were all reached and the problem appeared to be solved.

However I then got a call saying it had happened again after an injection had been made. The timing was undetermined as the injection had been made and the operator left the lab. They came back to find it alarming.

Having reset the system the issue again cleared so it doesn't seem like there's actually a leak at the inlet as surely it wouldn't be able to get up to pressure again if a leak had occurred. Checking the actuals confirmed steady pressure and flow at initial starting conditions. The method is set to constant flow.

I made an injection myself and watched to see what was happening. It seems the problems begin to kick in as soon as the ramp starts with the instrument beginning to beep. The pressure at the inlet climbs, as you'd expect, but the flow begins to drop steadily from set point of 1.07. The instrument then shut down about a minute after reaching final temperature at the start of final hold (240degC) and the flow was c. 0.6. Again, hydrogen safety shutdown on the display.

Does this seem like a settings issue in the method (I've checked the method and constant flow is selected) or something more sinister?

Any advice would be much appreciated.

[itspip]

Is the Hydrogen source a generator or a cylinder? I've had some strange things happen when overlooking how much gas is left in the cylinder; the GC would be okay at the ready state and inject, but right when the ramp started (or a few degrees into the ramp) it was shutdown in error. Hopefully it is as simple as that.

[uzman]

Did you replace the inlet ferrule ? May be the ferrule get loose during oven ramp.

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[AnaChem1983]

Is the Hydrogen source a generator or a cylinder? I've had some strange things happen when overlooking how much gas is left in the cylinder; the GC would be okay at the ready state and inject, but right when the ramp started (or a few degrees into the ramp) it was shutdown in error. Hopefully it is as simple as that.

It's a generator which supplies 3 other GC's in the same lab. No problems have been observed with the others which makes me think it's simply an issue with the GC in question.

I'm going to go through a few more checks this morning. The fact that the flow isn't maintaining at a constant level, which it should do, would certainly suggest a small leak. The fact that it's fine at the initial conditions puzzles me a bit though as I'd assume that if there was a leak it wound't be happy at these conditions either. Ditto with the ferrule on the inlet end of the column.

But if there's one thing I've learned from working with chromatography is that every day is an education! There's always room for something you've never seen before to crop up in the lab!

Thanks for your advice so far folks.

[Peter Apps]

What kind of injection are you doing - split or splitless? and are you using the gas save function during the run?

[Peter Apps]

What kind of injection are you doing - split or splitless? and are you using the gas save function during the run?

[AnaChem1983]

It's a split injection (20:1). The gas save function is being used during a run, yes.

[AICMM]

There are three things I would think right away. One, you do not supply enough flow to the inlet that it can maintain split and column at the same time. With, I assume, a 0.25 column this would be kind of unusual. But, you say it does it later in the run when the pressure has to rise to meet constant flow requirement. Gas saver set too low??

2nd - supply pressure is not sufficient for the EPC to maintain the higher pressure requirement at elevated temperature.

3rd - did you install the washer UNDER the bottom seal or on top? It has to be under - otherwise, I have seen "sealed" systems spring a leak in a run.


To the H2 generator Bozo, if you are not going to post a solution to the problem, don't post an advertisement.

Best regards,

AICMM

[Jake]

As AICMM points out, the shutdown occurs because the inlet EPC is unable to maintain pressure, for whatever reason. While all the recommendations so far are good, also have you actually checked all fittings in the line and around the inlet for leaks. I've been surprised in the past.

You have three GCs on the H2 generator. What are its specifications? Are you using it for fuel gas on all three too? Are they all running simultaneously, and what are the flows/spits?

[itspip]

With the three GCs all on one generator, which is fine or could be fine, I would try to shutdown the others and make an injection on the problem GC. If there ends up being no problem with the generator supplying to one GC then you know that the generator isn't supplying enough Hydrogen. If you still have an issue then there is probably a leak.

If you have a cylinder, you could supply the GC with cylinder H2, and if there is no issue then it's a supply from the generator problem. Otherwise you have a leak somewhere.

[Peter Apps]

It's a split injection (20:1). The gas save function is being used during a run, yes.

What happens if you disable the gas saver? (which at a total flow of 21 ml/min is not saving you much anyway).

[AnaChem1983]

Hi all,

I've resolved the issue! When I've inspected the inlet, part of the weldment assembly seems to be bent slightly and it didn't seem to be fitting securely to it's mooring point. I've rectified this now and things seem to be working OK. I'll keep an eye on this moving forward.

I'm told that, historically, there were issues with the hydrogen generator not being able to supply all 4 GC's with adequate pressures and therefore split ratios needed to be modified to get around this issue. So whilst this was a problem in the past I'm working on the assumption that any issues with hydrogen supply now would affect all 4 GC's and not just one?

I really appreciate everyone's advice on this issue so far.