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Hello gracious purveyors of isotope wisdom,

Following up:

- Starting with a dry and tight instrument (mass 18 = 352; mass 40 = 56 BF
off, split in)

- I took the reactor temp from 1450 to 1420 in an attempt to better hold
the deactivation.

- I deactivated by injecting 1 uL of hexane twice, separated by 20 mins.
Splitless, BF off, split out

- About and hour later I did my H3 (3.183) and started a run of a dilution
series (an actual dilution series, not just changing the split flow. All
runs are splitless.)

- The 'area effect' is still there. From 1.7 V to 7.5 V there was a ~ 20
permil depletion (bigger peak = more  depleted). This works out to ~ 3.4
permil/V.

- This feature is present across reactors... I've changed several.


Aaaand go.

Thanks for any thoughts.

Jeff





On Tue, Jan 17, 2017 at 1:21 PM, Jeff Salacup <[log in to unmask]>
wrote:

> Thanks, Paul.
>
> We're currently running at 1450, so I'm hesitant to get hotter.
> Deactivation seems like a possibility though, especially given the high
> temp we're running. Based on some of the reading I've done in the archives
> (too much vs. too little graphite in the reactor), it seems like an easy
> way to mess up the results. I'm going to recondition (deactivate) the
> reactor and see if that changes anything.
>
> Best,
>
> On Tue, Jan 17, 2017 at 12:09 PM, Paul Eby <[log in to unmask]> wrote:
>
>> Jeff,
>>
>>
>>
>> If your sample peaks show a size effect and your ref peaks don’t, then
>> the answer could be in the reactor. If the conversion process is
>> incomplete, you could easily get this result. You could try increasing the
>> reactor temperature or looking at the whether the tube is sufficiently
>> deactivated.
>>
>>
>>
>> I’m also curious about the dilution series that you run: are you changing
>> the concentration of the standard, or perhaps are you changing the split
>> flow to change the peak height?
>>
>>
>>
>> Paul Eby
>>
>>
>>
>>
>>
>> *Stable Isotope Lab Manager *
>>
>> *InnoTech Alberta *
>>
>>
>>
>> *TEL:* 250-483-3290 <(250)%20483-3290>  *CELL:* 250-893-5920
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>>
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>>
>> *From:* Stable Isotope Geochemistry [mailto:[log in to unmask]] *On
>> Behalf Of *Jeff Salacup
>> *Sent:* January-17-17 8:07 AM
>> *To:* [log in to unmask]
>> *Subject:* Re: [ISOGEOCHEM] dD and linearity after H3
>>
>>
>>
>> Thanks, Matheus.
>>
>>
>>
>> I've got an older GCC III that I have to manually adjust.
>>
>>
>>
>> So, if I do a series of on/offs, 8 refgas peaks, of increasing size from
>> 1 V to 10 V I get a much smaller effect of ~ 0.3 permil/V with an H3 of ~
>> 3.2 applied. This same H3 is applied to my alkane standards, but I still
>> have the effect I described above.
>>
>>
>>
>> Grumble...
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
>
>
> --
> Jeff
>
>
>
>
> *Two things are infinite: the universe and human stupidity; and I'm not
> sure about the **universe. - Einstein*
>
>
>
>
> *__________________________________________________________________**Jeff
> Salacup, Ph.D.*
> *Stable Isotope & Biogeochemistry Lab Manager*
> *UMass-Amherst*
>
>


-- 
Jeff




*Two things are infinite: the universe and human stupidity; and I'm not
sure about the **universe. - Einstein*




*__________________________________________________________________**Jeff
Salacup, Ph.D.*
*Stable Isotope & Biogeochemistry Lab Manager*
*UMass-Amherst*