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?
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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
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.