After reading all the helpful suggestions, I think there is one more thing
you may want to check. Are both your internal and external cold finger
temperature sensors stable? Especially when the external cold finger is
supposed to be maintained at -70 degree C for transferring the CO2 gas form
the external cold finger to the internal cold finger. If the external cold
finger temperature occasionally lower than -70, you may have incomplete CO2
transfer. On the other hand, if your internal cold finger occasionally did
not maintain the low enough temperature to freeze the CO2 gas, it may result
the similar problem too.
Dr. Horng-sheng Mii
Professor & Chairperson
Department of Earth Sciences
National Taiwan Normal University
Taipei, Taiwan 11677
R. O. C.
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Dave Mattey
Sent: Wednesday, March 18, 2015 9:07 PM
To: [log in to unmask]
Subject: [ISOGEOCHEM] Variable CO2 yields with Isoprime-Isocarb carbonate
I wonder if anyone can suggest reasons of the 'less obvious' variety why an
Isocarb system is producing poor isotope data related to variable CO2
reaction yields? This is the system that drops acid into evacuated Wheaton
vials and transfers the CO2 to the external cold finger.
The transducer readings of the CO2 yield are sporadically low, resulting in
the sample being aborted (too small), or if it runs, the isotope
compositions are anomalous. It is an intermittent problem, most yields are
good, but some are poor. I'd like them all to be good!
Sample size is in the 80-120ug range
Vacuum seems good
Acid is good quality (new batch just made, problem continues) Acid delivery
is consistent (i.e. present in all vials) There are no obvious blockages or
leaks on the gas line from the needle to the cold finger, which is working
Has anyone experienced this and found a reason that is not so 'obvious' as
no sample, no acid, vacuum leak etc? Any ideas appreciated!
Department of Earth Sciences,
Royal Holloway, University of London,