Hi Herb,
 
 
I realise this may sound like teaching my Granny how to suck eggs but have you considered recalibrating your magnet, or is the problem no signal whatsoever on the 44 cup when you do a magnet scan from 40 to 46 while admitting CO2?
 
What do you see when you run a magnet scan from mass 10 to 50? Do you get traces (and peaks for N2 background) on all 3 cups or only on minor 1 and minor 2?
 
If you see no 44 but what looks like 45 and 46 not coinciding when you just do a peak centre on CO2 this could just be caused by an off-set in HV or shift in magnetic field for any number of reasons; temperature, power surge or GOK. Based on the calibration table the system 'thinks' it is right on 44 but in fact has fallen completely off the peak.
 
Worst case scenario, the cup or channel for the major beam is stuffed.  Having said that, do you have the option to change resistor values for the cups electronically? If so, why not check this table in the configurator to see if perhaps a practical joker has changed that to something silly like 3 Ohm. Even if the value is what it should be , e.g. 3 exp+8 Ohm, change it to something more sensitive like 3 exp+9 Ohm or even 3 exp+10 Ohm and see if that makes a difference.
 
Similarly is the magnet setting for CO2 in the gas configurator at the value your last magnet calibration determined or does it show '???' ?
 
 
Best of luck,
 
Wolfram
 
 
****************************************
"Facts do not cease to exist because they are ignored."

Aldous Huxley, "Proper Studies", 1927
****************************************
Dr W Meier-Augenstein, CChem, FRSC
Principal Scientist - Stable Isotopes
Stable Isotope Laboratory
SCRI
Invergowrie
Dundee, DD2 5DA
United Kingdom
Tel.: +44 (0)1382 560025
Fax: +44 (0)1382 568544
Email: [log in to unmask]
 
Senior Lecturer (Assoicate Professor- Stable Isotope Forensics
Centre for Anatomy & Human Identification
University of Dundee
http://www.lifesci.dundee.ac.uk/CAHId/ <http://www.lifesci.dundee.ac.uk/CAHId/> 
 
Attention
This message contains privileged and confidential information intended for the addressee(s) only. If this message was sent to you in error, you must not disseminate, copy or take any action in reliance on it and we request that you notify the sender immediately by return email.
 
Opinions expressed in this message and any attachments are not necessarily those held by SCRI or any person connected with the organisation, save those by whom the opinions were expressed.

________________________________

From: Stable Isotope Geochemistry on behalf of Herbert Tobias
Sent: Thu 13/08/2009 15:43
To: [log in to unmask]
Subject: [ISOGEOCHEM] MAT252: CO2 Signals and Peakshapes


Hi All,

I am currently having a problem with signals for CO2 on a MAT252.  While admitting CO2 gas from the bellows, there is no mass 44 cup signal, and mass 45 and 46 cups do not overlap well.  The peak shapes are not flat, with spiking portions.  Since I cannot attach a picture to the ISOGEOCHEM list, below is a crude cartoon of a magnetic field scan around mass 40-46 for the mass 46 cup.  The mass 45 cup signal looks similar, but shifted over a bit.

                  /\     /\
                  |  \  /  \
       /\_____|   \/    \/\
___/                         \________

Anyone experience something like this before?  If sounds familiar, I can send a picture, offline, of a magnetic field scan with CO2 in the source for more detail if it helps.  

Thanks,
-Herb

-- 
Herbert J. Tobias
Cornell University
Ithaca NY 14853
1-607-255-9009 (Lab)

______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please visit http://www.messagelabs.com/email 
______________________________________________________________________


______________________________________________________
SCRI, Invergowrie, Dundee, DD2 5DA.  
The Scottish Crop Research Institute is a charitable company limited by guarantee. 
Registered in Scotland No: SC 29367.
Recognised by the Inland Revenue as a Scottish Charity No: SC 006662.


DISCLAIMER:

This email is from the Scottish Crop Research Institute, but the views expressed by the sender are not necessarily the views of SCRI and its subsidiaries.  This email and any files transmitted with it are confidential to the intended recipient at the e-mail address to which it has been addressed.  It may not be disclosed or used by any other than that
addressee.
If you are not the intended recipient you are requested to preserve this confidentiality and you must not use, disclose, copy, print or rely on this e-mail in any way. Please notify [log in to unmask] quoting the name of the sender and delete the email from your system.

Although SCRI has taken reasonable precautions to ensure no viruses are present in this email, neither the Institute nor the sender accepts any responsibility for any viruses, and it is your responsibility to scan the email and the attachments (if any).
______________________________________________________