Hi Toti,

We had a similar bubble-on-the-sample problem using a Multiprep device on a
VG Prism (dual-inlet) at the University of Florida, so I'm sure it's not
just a continuous-flow vs vacuum system problem. We also used cone-shaped
vials and a temperature of 90C. I don't recall exactly what the SG of the
acid was, only that we had to make it less viscous because we had
needle-clog troubles. Jason Curtis could give you more details on that.

We figured that the bubble was CO2 forming from the initial reaction, and
that the acid was too viscous for the gas to escape. Once the bubble
separated the acid from the sample, the reaction stopped. For such samples
we'd get no (or really bad) data.

I should add, that probably every time we saw the bubble-on-the-sample, it
was when we were trying to run tooth enamel apatite. We never saw this
problem with calcium carbonate standards like NBS-19.

I've now started to run carbonates on a GasBench. In that case we use
round-bottom exetainers. One disadvantage of the round-bottom exetainer is
that your sample is spread out on the bottom of the container and the acid
(viscous as it is) may not get to all of the sample if you use the small
amount of acid that was required for the cone-bottomed ones. I'm still
working out the details here.

I hope this is of help to you.


At 01:43 PM 6/20/2005, you wrote:
>I am trying to react carbonates using a GV Multiflow (Basically same Idea
>as GasBench as far as I can tell in that the H3PO4 reaction occurs in a
>helium environment and not a vacuum. So both camps are free to answer), and
>I noticed that after the H3PO4 was dispensed there was a tiny bubble at the
>bottom of my sample vial. This is obviously not a good thing. Has anyone
>experienced similar issues with continuous flow carbonate analysis? Is this
>one advantage the running with a vacuum system such as the GV multiprep?
>I am using 1ml Wheaton vials that have a cone-shaped bottom and the H3PO4
>has a sg. of 1.94. What bottom-shaped vials are people using with the
>GasBench or Multiflow? Maybe thats the problem. Reaction temp=90C
>Thanks in advance,
>Toti Larson Ph.D.
>Los Alamos National Laboratory
>Earth and Environmental Sciences                505.667.9894 (lab)
>Los Alamos, New Mexico 87545            550.667.8006 (office)

                       Dr. Pennilyn Higgins
                        Research Associate

   Stable Isotope Ratios in the Environment Analytical Laboratory

         Department of Earth and Environmental Sciences
         University of Rochester
         227 Hutchison Hall
         Rochester, NY 14627

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