Hi Rafael,

This is straight out of a Thermo GC-IRMS factory training manual I have.
Maybe it will help you with your leak check conditions and what specs to
look for.  Your background will be higher in splitless mode.

Conditions for leak test:

Set interface to straight mode
GC oven at room temperature
GC column flow 1.8-2.0 mL/min
Injector 20:1 split (40mL/min split flow)

--------------------------------------------------

Typical m/z 40 values:
Split out-- 10-20mV
Split in, Backflush on-- 10-25mV
Straight-- 20-40 mV (split: 40 mL/min)
Straight-- <200 mV (splitless)



Good luck, Ben


 
Benjamin Harlow
Washington State University 
School of Biological Sciences
P.O. Box 644236
Pullman, WA  99164-4236
 
Office:  509-335-6161
Lab:     509-335-6154
Fax:     509-335-3184
 
Laboratory for Biotechnology and Bioanalysis Stable Isotope Core
http://www.isotopes.wsu.edu
 

-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf
Of Rafael Núñez Gómez
Sent: Thursday, June 22, 2006 3:50 AM
To: [log in to unmask]
Subject: [ISOGEOCHEM] Argon background in direct mode GC IRMS

Dear GC-IRMS users
I am having some problems with my Ar backgrounds, possibly a leak in the 
injector. My current Thermo manual (Issue 06/2002) says that Ar (m/z 40) 
in cup 45 should be less than 50mV but did not say anything about split 
or splitless mode or wich flow. Present value is 80mV (split 
20ml/minute) and column flow 1.0 . Talking with Finnigan technicians it 
seems in the older manuals higher backgrounds, more or less what I have 
now, where considered OK. So, could any of you using the same system 
(Trace GC ultra and Delta plus XP with Trace DSQ as a second detector) 
give me your normal working values?. In backflush mode the flow is 
around 2.5 ml/minute and the He background for Ar is 7mV, Open Split is 
always on.
Thanks

Dr. Rafael Nuñez Gomez
Technician
Stable Isotope Service
Estacion Experimental del Zaidin CSIC
Profesor Albareda 1, 18008
Granada, Spain
Tf +34958181600 Ext 228