Chad,

These symptoms are consistent with a leak introducing oxygen. This can
quickly strip away your deactivation coating: reconditioning restores the
system, but it quickly degrades.

Paul Eby
InnoTech Alberta

> Hi all,
>
> I am hoping someone has seen these symptoms before because this is a new
> pattern to me in my decade of doing this.  We are running an Isolink II
> with a Delta V analyzing hydrogen isotope compositions of alkanes.  We are
> using the Indiana university B4 standard alkane mix for calibration
> (mixture of 15 alkanes of varying abundance and isotopic composition).
>
> We are seeing a progressive decrease in dD values for all alkanes in the
> mix, but particularly the short chains, in every subsequent injection
> (declining by ~5-10 permill per injection).  Then, at some threshold point
> (usually 4-5 injections in), the values jump enormously (as much as 100
> permill) across the board.  When we recondition the reactor by letting a
> dose of hexane move through as per manufacturer instructions, things
> return back to their original state and then progressively decrease with
> each subsequent injection just as before and the pattern repeats.
>
> As I mentioned, I have never seen this pattern before and have run
> thousands of these samples.  The fact that reconditioning seems to have
> such a large effect makes me think this is reactor related, but I have now
> swapped reactors and reconditioned 3 (!) different reactors and seen the
> same pattern on all of them.  I got very desperate and swapped out all
> lines going to the MCD device and the MCD device itself.  I swapped
> injector liners, inlet gold seal, septa, etc.  H3 factors are 3.5-4.0.
> Chromatography is gorgeous and backgrounds are low.  Flows all look good.
> But, alas, the problem persists.
>
> Anyone out there seen any behavior like this before??
>
> Thanks ahead of time and have a great weekend.
>
> Best,
>
> Chad Lane
>