HI Greg--

Good luck.....

Broken capillary in sampling needle??? You might just be sampling the 
input He, not the headspace gas. Try blocking helium ports on sampling 
needle, fingers work, and stick tip in water--see if it bubbles....

You can make your own if need be...

Other potential problems...

OK, is the "air" peak as big as it should be???

Check open split--capillary positions, piston height, and it's possible 
the sample line to the mass spec picked up a little dust and is 
partially clogged at the tip.

Flow through valco valve. You mentioned flow through purge line 
ok--check it in both load and inject modes. Compare it to the flow at 
the bulkhead--they should be close to the same.

take care

gerry


Henkes, Gregory wrote:
>
> Hello Isogeochemists,
>
> Our case of the Mondays has lasted until Wednesday… as often happens 
> with mass specs, we had a Monday problem and it is now Wednesday 
> problem. We are still looking for an answer. ISOGEOCHEM to the rescue 
> (or so we hope).
>
> Here is the issue: We are running carbonates on our GasBench II. As of 
> Friday last week we were getting beautiful data. Spot on. The first 
> run of the week (Monday) we had acid dropping issues (not what you 
> think). We had some samples where the acid didn’t drop and 
> consequently no samples peaks appeared for those. We fixed the acid 
> issue (blocked lines) then, on Tuesday, we were looking at 
> chromatograms (all of them) where the acid had dropped fine but still 
> there were no peaks. You could only see the small, quicker Valco ‘air’ 
> peaks which normally proceed the larger sample peaks. We took this to 
> mean that our problem was in front of the Valco valve as clearly gas 
> was moving to the MS from there on. To be sure we checked flow rates 
> in (and out) of the GC… they were all fine. We are getting good flow 
> out of the purge Valco port in Load position and our Nafion tubes look 
> normal. Both the He fill and the sampling needles are fine as well as 
> their capillaries form the GC Pal to the GasBench II. Today, as a last 
> resort I ran a dumby exatainer vial full of my frustrated breath (our 
> 3% CO2 in He has grown legs and walked out the door) and still NO 
> sample peaks.
>
> Also, the reference CO2 peaks look great… I suspect it is not a mass 
> spectrometer issue.
>
> Any thoughts, ideas, or rituals that we could perform to get this 
> thing up and running would be appreciated… thanks all!
>
> Cheers,
>
> Greg
>
> Gregory A. Henkes
>
> Research Fellow
>
> Museum Conservation Institute
>
> Smithsonian Institution
>
> 4210 Silver Hill Road, MRC 534
>
> Suitland, MD 20746-2863
>
> 1.301.238.1253 (desk)
>
> 1.301.238.1262 (lab)
>
> 1.301.238.3709 (fax)
>