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 >> <(250)%20893-5920> >> [log in to unmask] >> >> >> >> Vancouver Island Technology Park >> #3-4476 Markham St., Victoria >> BC, Canada V8Z 7X8 >> >> >> >> *InnoTechAlberta.ca* >> >> >> >> *This communication may contain confidential, personal and/or privileged >> information. Please immediately contact the sender if you are not the >> intended recipient of this communication. If you are not the intended >> recipient of this communication, disclosure, copying, distribution, use >> and/or reliance of this communication is strictly prohibited. Any >> communication received in error, or subsequent reply, should immediately be >> deleted or destroyed.* >> >> >> >> >> >> >> >> *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*