Hi Charlotte
Your amplifier zero might be wrong.  Try resetting the amplifier zeros: no gas, source off before reset.

Gilles

Gilles St-Jean
Chercheur / Research Scientist
Université d'Ottawa / University of Ottawa
Sciences de la Terre / Earth Sciences
140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5
Tel: 1-613-562-5800 xt 6830 (Bureau / Office)
                    xt 6839 (Bureau / Office Lab)
                    xt 6836 (IRMS lab)
Téléc. / Fax: 1-613-562-5192
Courriel / E-mail: [log in to unmask]
Toile / Web: www.isotope.uottawa.ca

 

> -----Message d'origine-----
> De : Stable Isotope Geochemistry 
> [mailto:[log in to unmask]] De la part de Charlotte Lehmann
> Envoyé : 31 août 2006 12:20
> À : [log in to unmask]
> Objet : [ISOGEOCHEM] Negative Mass45 BGD values
> 
> I am wondering if anyone can suggest why the Mass45 
> background (BGD) value would be negative, and how to correct 
> for this. I am also getting very depleted isotopic values to 
> go along with the negative BGD value.
> --
> Charlotte Lehmann
> Research Technician
> Bates College
> Department of Geology
> 206A Carnegie Science Building
> 44 Campus Avenue
> Lewiston, ME 04240
> Phone: 207-786-6485
> FAX: 207-786-8334
>