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Dear Stan,
I am very much aver of your paper,  but I thought it would be better to
start with a method which was originally developed for this system.
Regards:
Kinga

Kinga Revesz
Chemist, Stable Isotope Laboratory
U.S.Geological Survey
MS 431
Reston, VA 20192
T:703-648-5865
FAX: 703-648-5274



                    Stanislaw Halas
                    <[log in to unmask]        To:     [log in to unmask]
                    LUBLIN.PL>                cc:
                    Sent by: Stable           Subject:     Re: S isotope of BaSO4
                    Isotope
                    Geochemistry
                    <[log in to unmask]
                    VM.EDU>


                    02/04/00 12:10 PM
                    Please respond to
                    Stable Isotope
                    Geochemistry





Dear Kinga and S-34 Analysts !

I would like to turn your attention to a new paper:

S. Halas and J. Szaran (1999)  Low -- temperature  thermal
decomposition of sulfate to SO2 for  on -- line  34S/32S  analysis,
Anal. Chem. 77, 3254 -- 3257.

In this method we obtained total conversion of sulfate sulfur to
SO2 at temperatures 650 to 700 C in a few min. in presence of
NaPO3. This reagent and BaSO4 sample we put into Cu foil
which trapt excess of oxygen released from sufate.
So far we used this method with a glas line connected to
the inlet system. However it may be good for CFMS because
it is rather insensitive to temperature in the oven.

The only differences are in  T  and metal envelope (Cu instead Sn).

With best wishes,
Stan Halas

> Date:          Fri, 4 Feb 2000 09:59:07 -0600
> Reply-to:      Stable Isotope Geochemistry <[log in to unmask]>
> From:          "Kinga M Revesz, Chemist, Reston, VA (Kinga Revesz)"
>                <[log in to unmask]>
> Subject:       S isotope of BaSO4
> To:            [log in to unmask]

> Hi All,
> Now, that S is in the "air" again, I decided to send a version of my
notes
> to the list members also, previously sent to other laboratories.   At
USGS,
> Reston Isotope Laboratory we have been running S isotope of BaSO4, C and
N
> of organic compounds,  N of soil samples etc. by hundreds now
successfully.
> Bruno Lavettre at Castech helped  me troubleshoot the system, thanks for
> that Bruno.  Frank Trench was very helpful with the MS, and Peter Stow's
> help at IsoMass was priceless with the Conflow interface.
>
> Short summary of running S isotope of BaSO4 on the Carlo Erba EA 2500 -MS
> Delta Plus system:
> I.  EA set up:     "Flash point"
> The fact that the melting point of the BaSO4 is 1580 C and the reactor
> temperature is only 1020 C could create difficulties in the analysis of S
> isotope of BaSO4.  The "flash point" has a higher temperature, around
1800
> C, (since the Tin oxidation reaction is exothermic); therefore it is
> critical to use it well by creating a sharp, sudden, bright and single
> flash.  This should be done by coordinating: 1.  He pressure and flow
rate,
> 2.  Oxygen pressure and flow rate, and 3. Sample start time. In fact, the
> system is so sensitive, that, for example, even a one-second difference
in
> the sample dropping time can make a difference in the look of the flash,
> peak shape and, consequently, the isotope result.  The optimum set-up in
> our system is: Cycle 100, Oxy 60 (O2 flow stops flowing into auto
sampler),
> Sample Start 10, and Sample stop: 40.  The Helium regulator is set for
150
> KPa, He flow Setup is 105 mL/min which measures 120 mL/minute at vent.
The
> Oxygen regulator is set for 150 KPa, and oxygen flow rate is 54 mL/minute
> at Purge. Oxygen loop is 5 mL.  Sample size is around 0.2 -0.3mg (BaSO4).
> We DO NOT use V2O5 because it is toxic, and it is a catalyst for SO3
> production and should be avoided.  It might help stabilize the so called
> oxygen effect by providing constant sours of oxygen in the combustion,
but
> I have never saw a study on that.  Even then, it might help the accuracy
> but not the precision of the result.
> II.  Leak in the system:
> Even a tiny leak could interfere with the result; it could create doubled
> peak shape, and unstable run etc. The high He flow rate makes the system
> more sensitive to leaks (Bernoulli principal).  Leaks could cause changes
> in the flow rate in an uncontrollable manner, which could interfere in
the
> quantitative combustion, in the peak shape, and consequently in the
isotope
> value.
> III.  Ashes in the reaction tube.
> Ash accumulation is also critical.  Although Tin oxide serves as a
catalyst
> in the reaction,  it also partially "clogs" the system interfering with
the
> flow rate, though not necessarily in a measurable manner.  This is,
> however, a "controlled interference" causing a shift in delta values.  By
> running frequent standard materials, this shift can be corrected.
> However, after around 50 samples (1 carousel) it is healthy to remove the
> ashes.
> IV.  Standard gas:
> We use SO2 ANHY by  Matheson,   small cylinder around 15 lb.  We do not
> have any problem with this gas.
> 11 psi gives us 1.3 V signal in Cup 1.  The length, ID and sometimes OD
of
> the capillary are critical, so does their location in the conflow.  (We
all
> know that.)
> V.   Mass Spectrometer:
> Should be focused very carefully (I am not going into details here).  It
is
> temperature sensitive, so it should be operating in a temperature
> controlled environment with all the side panels on.  We use resistor
1*10E9
> for Cup1, and 2*10E10 for Cup2.
> Internal precision check:
> Zero Enrich method (standard gas on/ off 10 times) should give 0.1 per
mill
> or better standard deviation, and the Ratio Linearity test should give
0.12
> per mill/Volt or better linearity.
> External precision check:
> Linearity test with same reference material should give standard
deviation
> 0.2 per mill at n=16, between sample weight 0.15 - 0.500 mg BaSO4.
> If this is not satisfied, one should try to run the same sample size
only.
> Precision should be for n=10 0.2 per mill.
> If neither of the criteria has been met, the system is useless and the MS
> should be refocused.
> VI.   Sample preparation.
> It is recommended to dry the sample overnight at 110 C, and weigh it as
> soon as it removed from the oven.   Before weighing, careful
homogenization
> should be done in an agate mortar and pestle.   We run 3 same standard
> materials first, than alternate 10 unknowns and 2 standards.    We use
> standards NBS 127 and IAEA SO6, delta S= 20.91 and -32.85 respectively,
and
> correct our data for slope and intercept.  If you have LIMS (Laboratory
> Information Management System) for light stable isotopes created by
> T.B.Coplen, it can do it for you.
> Reference:  A.Glesemann et al. Anal.Chem. 1994, 66 2816-2819.
>      T.B.Coplen, U.S.G.S. Open-File Report 98-284.
>
>
> Kinga Revesz
> Chemist, Stable Isotope Laboratory
> U.S.Geological Survey
> MS 431
> Reston, VA 20192
> T: 703-648-5865
> FAX: 703-648-5274
>

==============================
Professor Dr. Stanislaw Halas
Mass Spectrometry Laboratory
Maria Curie - Sklodowska University
20-031 Lublin, POLAND
tel: (48 81) 537 6275    fax: (48 81) 533 3669