Print

Print


Andy,
we have had problems with acid getting in the sample needle and capillary
also, and the acid pump allowing drops to hang on the acid needle despite
back-pumping. During and after any carbonate runs, we carefully watch the
sample needle capillary, holding up to light to see any tiny acid droplets.
Also, you generally get enough clogging to cause small or absent sample
peaks. If clogging occurs, remove the needle and capillary and attach a
small disposable syringe to the capillary end using an adapter you can make
with a 1/16" valco union and ferrule/nut for the capillary. The syringe tip
will fit tightly into one end of the union. Slowly draw deionized water
from a beaker through the needle and capillary using the syringe, repeating
many times until the ejected water has near-neutral pH. Then repeat with
methanol and dry in an oven at 90C or so. It is good to keep a spare to
swap while the other is drying. Also, if you get any particle clogging,
don't poke into the sample needle more than a couple mm, or you'll ruin the
internal capillary connection. It is glued in place, and the capillary of
course has a polymide coating, so any heating must be gentle. We have also
had problems removing the ferrules from the top of the GasBench, so we
generally re-use them unless there is a helium leak. Just don't overtighten
and they seem to work fine.

We also had resorted to injecting acid by hand, going to the opposite side
of the septum from where the sample needle enters, but still had problems
at times. We also see the tiny acid droplet on the bottom of the septum. I
recently discussed all this with Finnigan, and they recommend keeping the
acid pump at the minimum volume and lowest belt setting, so that it takes
about 10 pumps to get a drop of acid. This should allow proper back-pumping
to remove any residual drops. They are standing behind the system and are
committed to it working correctly, but it takes some dialing in. Also check
the o-ring seals on the acid lines, because air will cause problems.
Heating the pump body with a heat gun initially seems to get things flowing
faster. Make sure the pump is not  powered when you move the belts around,
or you can get a nasty shock.
Jon



At 09:53 AM 12/2/2003 -0700, you wrote:
>I know there has been some discussion of clogged Finnigan Gas Bench needles
>in the past but the Isogeochem Archive seems to be down so I can not check
>it.  I have used my gas bench for hundreds of CO2-H2O equilibrations with
>no trouble.  Now I am trying to run carbonates for the first time.  So far
>I have found it easier to manually flush the vials and then manually inject
>the acid.  After that I will use the autosampler to extract the CO2.  Just
>as I was starting I managed to break the gas bench  needle by forgetting to
>put the lid on the heating block.  So I installed a new needle (which was a
>trial in itself trying to get the old graphite ferrule out.) Now after
>running only about 10 samples the needle is clogged with crystallized
>phosphoric acid.  I could easily see it in the needle with my hand
>lens.  We have been attempting to inject the acid toward the edge of the
>septum (away from where the sampling needle enters) and then wipe off the
>drop of excess acid that seems to accumulate there.  There is also a drop
>on the bottom side of the septum that we can not get at.
>
>So I have two questions:
>
>1)Has anyone had any luck unclogging the needle when it has acid in it?
>2) What steps do I need to take to keep this from  happening again.?
>
>Thanks
>
>Andy
>
>
>
>**********************************************
>Dr. Andrew R. Campbell
>Professor of Geology
>Department Chair
>Dept. of Earth and Environmental Science
>New Mexico Tech
>Socorro NM 87801
>Research office: 505-835-5327
>Chairman's office: 505-835-5635
>Fax:   505-835-6436
>e-mail: [log in to unmask]
>www.ees.nmt.edu
>**********************************************

Jonathan D. Karr, Ph.D.
Technical Director, Duke EnVironmental stable Isotope Laboratory (DEVIL)
Duke University Dept.of Biology & Nicholas School of the Environment and
Earth Sciences
National Phytotron, Box 90340
Durham, NC 27708-0340
(919) 660-7418
Fax: (919) 660-7425
[log in to unmask]
laboratory website: http://www.biology.duke.edu/jackson/devil/




Adversity is an opportunity