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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