Dear All,

I would like to aware those who roast organics (I mean even impurities in 
carbonates) in vacuum.
This may lead to bad background around masses 44 to 46, which in 
consequence may result in highly positive delta values, of coarse 
UNRELIABLE!!!!
Roasting should be done in a stream of He carrier gas which sweeps the 
sample to be analyzed.

Cheers,   Stan


At 13:54 06-12-05 -0300, you wrote:
>
>
>
>----------
>Dear all
>
>I have made a lot isotope analyses on gray and black limestones from 
>differnt localities of the Precordillera, Argentina.  First without 
>roasting and then roasted.   I do not know if in any case obtained the 
>actual values.  The only thing I know is that after roasting I coud get 3 
>replicates of each sample within 0.1 %o  and witn no roasting differences 
>of 1 %o or more.  If you plot the traces of ratios measured in the MS they 
>are not parallel, but they increase or decrease linearly during the 
>measurement.  I used to roast the samples at 300 ºC under vacuum.
>regards,
>
>Héctor O. Panarello
>Director
>INSTITUTO DE GEOCRONOLOGÍA Y GEOLOGÍA ISOTÓPICA (INGEIS)
>Pabellón INGEIS - Ciudad Universitaria
>1428 Ciudad de Buenos Aires
>Tel: +54-11-4784 7798
>Fax  +54-11-47833024
>

Dr. Stanislaw Halas
Mass Spectrometry Laboratory
Institute of Physics, UMCS
20-031 Lublin, Poland
phone: +48 81 537-62-75
fax: +48 81 533-36-69