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Hi Melissa,

 Can I ask you a few question in conjunction with the below?

1. What is the temperature setting for the injector?
2. What's the average concentration per FAME in your FAME mix (in nmol/microL)?
3. Have you looked what the chromatogram looks like for a dummy run (no injection or neat solvent only)?
4. Same as point 3 but for single compound sample, say 10:0 or 12:0.
5. Is your system fitted with a FID and a cross-piece prior to the oxidation recator?

Best,

Wolfram


________________________________
From: Stable Isotope Geochemistry [[log in to unmask]] On Behalf Of Melissa Bautista [[log in to unmask]]
Sent: 19 January 2008 06:14
To: [log in to unmask]
Subject: [ISOGEOCHEM] GC-c-IRMS

Hello,

I have been running FAMEs on our GC-c-IRMS using a 30m DB-5 column with 5m of guard column. The first six samples returned good peak resolution. After the sixth, I now get very poor resolution. Instead of well-defined peaks at the expected retention times, I'm getting hundreds of peaks at low amplitude (<100mV) throughout the run.
The GC method I'm currently using is as follows:
90-280C, 3C/min., 20 min hold; Flow rate 1.2 ml/min. He; Injection: splitless w/ surge.
Can anyone tell me what's happened, and how it might be fixed?

Thanks
Melissa D. Bautista
IRMS Research Technician
Centre for Coastal Biogeochemistry
Southern Cross University
P.O. Box 157 Military Road
Lismore NSW 2480
Phone (02) 66 269 565
Mobile 0431928278