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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