Lastly, I believe I neglected to mention that carbon does not change in the 
samples where we observed shifts in oxygen between 0 and 200C.


At 01:32 PM 12/5/2006, you wrote:
>Hi Stan
>
>
>I forgot to say that ratios of roasted limestones are only slightly higher
>(< 0.5 between triplicates)that those not roasted.  The effect on the record
>of the MS ratios (ratio non constant but increasing with time) was only
>produced in non roasted limestones and disappeared after roasting.  The
>manual of the Micromass 602, that I used during that time (early '80),
>explained the line's shape as "changing background at minor mass".
>Best regards,
>
>Héctor
>
>
>
>-----Mensaje original-----
>De: Stable Isotope Geochemistry [mailto:[log in to unmask]] En nombre
>de Stan Halas
>Enviado el: Martes, 05 de Diciembre de 2006 02:38 p.m.
>Para: [log in to unmask]
>Asunto: Re: [ISOGEOCHEM] RV: [ISOGEOCHEM] Carbonate roasting temperatures
>and other pretreatments
>
>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
>
>--
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Lora L. Wingate
University of Michigan
Department of Geological Sciences
Stable Isotope Laboratory
1100 North University
1013 C.C. Little Building
Ann Arbor, MI 48109-1005