Hi all,

I thought I had a problem with our Gasbench resolved just before the Christmas break started, but now we’re back to where we started (2 sample peaks) for some unknown reason.

Can anyone recommend a flow rate meter that would work well with the Gasbench?

Thanks,

Joe


On Dec 21, 2016, at 2:00 PM, Paul Eby <[log in to unmask]> wrote:

That’s great! It has to be a relief solving a big problem right before Christmas holidays!
 
Paul
 
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Lambert, Joe
Sent: December-21-16 11:55 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Gasbench Bulkhead Union question
 
Paul, you’re the man!  6th time was the charm apparently.  I now have 10 sample peaks after changing the sample needle for the 6th time.   
 
Thanks!
 
Joe
 
 
 
On Dec 21, 2016, at 12:35 PM, Lambert, Joe <[log in to unmask]> wrote:
 
Hi Paul,
 
I’ve tried 4 or 5 different needles.  That said, it could be that I’ve had multiple issues, resolved all but the currently attached needle, which hasn’t been swapped out in quite some time.  I’ll give it a try and see if that helps,
 
Thanks!
 
Joe
 
 
On Dec 21, 2016, at 12:13 PM, Paul Eby <[log in to unmask]> wrote:
 
Joe,
 
A possible explanation lies in the two-hole needle: it’s not impossible for the helium out from the gasbench to go to the needle, then back to the gasbench without actually mixing in the vial! If the glass capillary tube inside the needle was to be broken, the pure helium flow could enter there and not enter the vial. I’ve also seen this in a two hole needle where the glass capillary tubing was not effectively sealed at the tip of the needle with glue. 
 
Short of taking the two hole needle apart, do you have another you could swap in? Or, take it off and attach separate needles to both the supply and return line so you can manually test?
 
Paul Eby
 
Stable Isotope Lab Manager 
InnoTech Alberta
 
TEL: 250-483-3290  CELL: 250-893-5920
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From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Lambert, Joe
Sent: December-21-16 9:38 AM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] Gasbench Bulkhead Union question
 
Hi all,
 
Thank you for the feedback and troubleshooting ideas.  Let me give a quick update.
 
Over-pressurized tubes due to flushing:
There was a little hissing of escaping gas when I insert a needle through the septa of a flushed tube.  However, I have the same behavior (1st sample peak only) when attempting to measure this tube where the He+CO2 has been brought back down to atmospheric pressure.  Additionally, we have a method we use for measuring CO2 from air samples (atmosphere pressure) and have the same result (missing peaks).  I also flushed some tubes on the troublesome Gasbench and then measured them on a separate Gasbench + Delta Plus and we get 10 beautiful sample peaks.  Hopefully these 3 tests confirm the issue is not related to flushing (over pressure).
 
Some have mentioned potential problem within the Gasbench (rotor seals, clogs in or near the GC, movement of Valco switching time events, etc.).  I get 10 perfect sample peaks if I run He+CO2 directly from the He+CO2 (flush) bulkhead to the sample “intake” bulkhead using a short piece of fused silica (bypassing the needles altogether).  Wouldn’t this test rule out issues within the Gasbench (rotor seals, clogs in or near the GC, movement of Valco switching time events, etc)?  Today I ran this same test both with the Flush-fill “on” and “off” (high vs. low flow rate) and get 10 perfect sample peaks every time.
 
To me, all of this points to a problem with the He flow coming out of the GB into the sample needle (Needle by-pass test does not test that flow path).  I have “rebuilt” that connection, including replacing the bulkhead union, 3 times now with no improvements.  I still do not have a way to measure absolute flow rates, but I get bubbles out of that small capillary coming out of the manifold (the He line that pushes He through the sample needle.  If I attach that capillary to the bulkhead, attached a sample needle to the topside of that bulkhead, place a tube on the sample needle, I get bubbles out of the capillary running out of the sample needle.  If I reattach that sample needle capillary to the bulkhead (sample gas intake), I get bubbles out of the vent on the Valco (load mode).  Hope that makes sense.  Perhaps I’m getting enough flow to give me bubbles (or detectable by the He flow meter), but not good enough flow for proper peaks.  Can anyone offer advice for the connection of the small capillary coming out the GB manifold (He line to sample needle) and the underside of that bulkhead union?  Should it be tightened as gently as possible?  Should it be tighten more than you would think?  Should the capillary only be insert halfway in the ferrule?  Again, I’ve reconnected this 3 times so it seems unlikely that I’ve attached it incorrectly each time.  Regardless, I’m not getting proper sample peaks.  All I want for Christmas is 10 sample peaks! 
 
Thanks for the input everyone.
 
Joe






Joe Lambert, PhD | Research Scientist
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Geological Sciences 
The University of Alabama 
2028 Bevill Building, Tuscaloosa, AL 35487
office 205-348-4404 | mobile 205-792-2148 
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