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.
> 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.
> Chad Lane