Hi Todd
It is dificult to say what is normal in a system where so many variables are 
affecting the backgrounds, but here are my values for samples measured 
recently.

With backflush off (direct mode), Open Split In, Oven 40°C, Flux 1.3ml/min., 
Split inyector 1:20
H2O 7mV, N2 1035mV, Ar 50mV, CO2 5mV. All measured in Cup 2. Combustion and 
reduction reactors at 950°C and 650°C respectively.
With backflush On the values have to be quite better. I normally have a look 
to N2 and if the value is higher than 2 volts then I wait (after changing He 
bottle) or I look for a leak. I have found that tighten the septum cup help 
a lot.
Good luck
Rafael

Dr. Rafael Núñez Gómez
Colaborador I+D+I
Servicio de Isótopos Estables
Estación Experimental del Zaidín CSIC
Profesor Albareda 1, 18008 Granada, Spain
Tf +34958181600 Ext 228
fax +34958129600




----- Original Message ----- 
From: "Todd Prior" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, May 07, 2007 9:07 PM
Subject: [ISOGEOCHEM] High Argon?? Appropriate Background Levels


Thanks go out to a contributor named Julie (my email are forwarded and then
deleted so I could not reply to it as sent) from her email suggesting that
my Ar values could be high due to a new He tank. I had checked N2 levels and
they are not high in fact they lower than AR which doesn't.sound like a 
leak...

DOes anyone know the correct specs for N2 Ar Co2 H2O in the various cup when
checking for background levels on a Delta XP??