I fully agree with all statements written before. If this does not help you might also try to extend the time of your run to monitor if the peak arrives later?
No very likely in your case if flow is too low this might be an option. We once had this with Extainers that were pre-evacuated and then sample CO2 injected into them. We analyzed them with our normal procedure (120sec transfer time). However, we ignored the fact that they had under-pressure and so the peaks arrived later in the Valco and GC. The pattern was similar to what you describe. We saw a very nice first peak and then - nothing.
However, the “first” peak was in fact the last(!) peak of the sample before. After the autosampler removed the needle from the vial, the sample CO2 just stayed in the silica transfer capillary (no flow) but started to move on when the needle entered the next vial and flow was re-established.
And: in IRMS no stupid problems exist. :-)
> Am 28.02.2018 um 18:30 schrieb Higgins, Pennilyn <[log in to unmask]>:
> Greetings all,
> I am having what may be categorized as a 'stupid' problem.
> Two weeks ago, there was a clog in the sample side of our Gasbench. I found the clog (or so I thought) at the end of the sample needle capillary. I replaced the needle, and tried to resume analyses.
> I wasn't seeing any sample gas (the reference side seemed fine), so I started fiddling...
> I have since:
> Cleaned the Valco;
> Replaced the nafion in both water traps;
> Checked for blockages in the GC;
> Taken apart and reset the sample open split;
> Checked for blockages at the ends of the capillaries entering the source;
> Checked the vents on the Valco to make sure they're venting;
> Made sure that the He lines are actually connected so we have gas flow;
> ...and probably some other things, including tearing out my own hair.
> For the last several days when I try to run an analysis, the reference peaks are normal but I only get one sample peak (the first one), instead of the 10 peaks that I expect. That first peak looks just fine. If I zoom in really really close, I can see the other 9 peaks as little 10-20 mV bumps along the trace.
> I've loosened things, tightened things, checked fittings, and done lots of fiddling about, but I'm getting nowhere. Clearly, I am too close to this problem and I'm missing the obvious.
> Please help me! What am I missing?
> Dr. Penny Higgins
> Stable Isotope Ratios in the Environment, Analytical Laboratory - SIREAL
> Department of Earth and Environmental Sciences
> University of Rochester
> [log in to unmask]
PD Dr. Robert van Geldern
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) | GeoZentrum Nordbayern
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