Remove the line in the front of the EA. Easiest. Marilyn
On 9/10/19, 10:33 AM, "Stable Isotope Geochemistry on behalf of
Arnold,Thomas E" <[log in to unmask] on behalf of [log in to unmask]>
>We have been using the same UHP tank of N2 for some time now (predating
>the issue at hand).
>I have not baked the GC oven in the EA before. When you say vent the EA
>away from the conflo, can I do this by simply turning off (in insodat)
>the high flow capillary that is going into the conflo? If I remove the
>line in front of our Costech EA that is carrying the gas from the machine
>to the conflo, the N2 backgrounds skyrocket (as expected). Thus, Iım not
>sure which is the best way to vent it away from the conflo.
>> On Sep 10, 2019, at 12:37 PM, Harlow, Benjamin <[log in to unmask]> wrote:
>> EXTERNAL EMAIL: Exercise caution with links and attachments.
>> Hi Tom,
>> What are your backgrounds? You could have a bad tank as well. Have any
>>been changed recently? If 30 is increasing throughout your EA sequences
>>it could be that the water scrubbing chemicals are not good, or there is
>>a pathway through the trap. When was the last time the GC was baked? (Do
>>this with the EA vented away from conflo)
>> What I meant about instability is that is usually a consequence of
>>excessive water. If you have good N2 on-off stability then I would think
>>the water in your system is manageable. Usually, when we see a strong
>>stair step effect in m/z 30 N2 is not reproducible to 0.06 per mil or
>>better. If N2 is continually flowing into the source you will see 30
>>rise. But with time it should return down.
>> It is my understanding that if heaters are off, water is still likely
>>hanging around the source but you may not see a large m/z 18. Compared
>>to leaving heaters on all the time, the water background will be much
>> If your system doesn't seem stable, it may be worth it to close the
>>inlet, turn on all heaters and let the system pump for a day or two then
>> -----Original Message-----
>> From: Stable Isotope Geochemistry <[log in to unmask]> On Behalf
>>Of Arnold,Thomas E
>> Sent: Tuesday, September 10, 2019 6:52 AM
>> To: [log in to unmask]
>> Subject: Re: [ISOGEOCHEM] Mass 30 instability on Delta V
>> Ben (and others),
>> Thanks for the quick response, we also assumed water in the system. As
>>a follow-up: why would the m/z 30 signal increase throughout a single
>>run and across multiple runs? You mention instability as a reason. What
>>do you specifically mean by this? That the EA is not properly sealed?
>>Itıs also strange because we see this issue when the EA/high flow is
>>disconnected from the IRMS and the on/off runs are through the conflo.
>> Thanks again,
>>> On Sep 9, 2019, at 5:39 PM, Harlow, Benjamin <[log in to unmask]> wrote:
>>> Hi Tom,
>>> It is likely elevated water in your system. N from your N2 pulses
>>>combines with O from H2O to give you m/z 30. More time will help. We
>>>typically run with source and inlet valve heaters on all the time to
>>>keep water out. Sometimes a heat gun or hair dryer can be beneficial to
>>>drive water off other components. Monitor m/z 18 while heating various
>>>components. Watch for the signal to climb, eventually drop and
>>> Every time you replace reagents or open up the EA more m/z 18 can get
>>>in your system. So venting the EA or allowing ample stability time is
>>>needed. If water is really bad then close the IRMS inlet and allow it
>>>to pump down independently.
>>> Usually if m/z 30 does the stair step on std on offs it is not a
>>>stable condition for us.
>>> Regards, Ben
>>> -----Original Message-----
>>> From: Stable Isotope Geochemistry <[log in to unmask]> On Behalf
>>>Of Arnold,Thomas E
>>> Sent: Monday, September 09, 2019 2:04 PM
>>> To: [log in to unmask]
>>> Subject: [ISOGEOCHEM] Mass 30 instability on Delta V
>>> To the great minds of the list serve,
>>> Our system: Delta V coupled to a costech EA via conflo IV
>>> Our issue: Mass 30 is drifting to higher and higher voltages across
>>>multiple N2 on/off runs more than a 1V increase from our first to
>>>fourth on/off. I can send pictures to individual emails if needed.
>>> What we've tried thus far: 1)Replaced: the seals on the EA reactors,
>>>the copper wires in the reduction reactor, the water trap. 2) We turned
>>>on the heater to bake out the source and inlet. I believe this heater
>>>operates at a temperature of 50-80C. After the bake out, the amplitude
>>>of mass 30 was reduced, but the voltage drift was still there. 3) The
>>>problem presents itself in both EA mode and in the conflo only mode.
>>> Any suggestions on what to do? Should this even be considered a
>>>problem as our standard deviation looks fine after the 3rd series of
>>> Elliott Arnold
>>> Pitt Geology