Dear Linda,

Certainly such high delta 13-C values do not look normal to me. Without
knowing further details of your procedure it is difficult to say where the
problem might be.

However, when I was trained in the use of the guanidine method at SURRC
some years ago, I remember Terry Donnelly stressing how important it was
not the let the phosphoric get in direct contact with the solid reagents +
reaction products. Otherwise, HCl may form, and from then on, anything can
happen.

We have never found similar problems to the ones you describe, but then we
have always been very careful about our analytical procedure, and never let
into the mass spec a "suspicious" sample ... For what I read in Wenbo
Yang's response, you better follow his advice.

If you feel it might be of help, I can send you our detailed "recipy" for
the method ...

Good luck,

Clemente


>Dear list members,
>
>I would be interested in hearing from anyone who is or has been using
>guanadine hydrochloride as a reagent for determining oxygen isotopes in
>water.
>
>Starting off with an internal lab standard of milli-Q water, we have found
>that our 45/44 ratios are huge - giving delta 13C of well over +150 when
>run against TS limestone (but no doubt contaminating the reference gas so
>these values are probably too low).  These ratios could be real and a
>consequence of the manufacturing process of GuHCl (the batch of GuHCl I
>have was purchased from Aldrich), or there is an (hydrocarbon?) isobaric
>interference on mass 45.
>
>Have other people found something similar, and if these high 45/44 ratios
>are real, what sort of reference gas was used to get decent analyses?
>
>thanks in advance,
>
>Linda Godfrey
>
>_____________________________________________________
> Linda Godfrey
>
>Department of Geological Sciences                       tel (607) 255 0058
>Cornell University                                      fax (607) 254 4780
>Ithaca, NY 14853                               [log in to unmask]
>_____________________________________________________

-----------------------------------------------
Dr. Clemente Recio
Stable Isotope Laboratory
Fac. de Ciencias
Univ. de Salamanca
E 37008 - Salamanca
      Spain

Phone: (+34) 23 29 44 00 Ext. 1540
Fax:   (+34) 23 29 45 14
E-mail: [log in to unmask]
-----------------------------------------------