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Dear Andrew, Ian and others,

The same approach as described by Ian was published by:

Krishnamurthy R. V., Atekwana E. A., and Guha H. (1997) A simple,
inexpensive carbonate - phosphoric acid reaction method for the analysis of
carbon and oxygen isotopes of carbonates. Anal. Chem., 69: 4256-4258.

My two eurocents,
Pier.

**********************************************************************
Dr. Pier A. de Groot
Pastoor Moorkensstraat 16
2400 Mol - Achterbos
Belgium
Tel. +32 (0)14 326 205
e-mail: [log in to unmask]

Visit my WEB-site about my ³Handbook of Stable Isotope Analytical
Techniques² at:
http://users.pandora.be/handbook/index.html
last update: 6 October, 2003.
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> Dear Andrew (& others)
>
> We have experienced similar problems with acidification. We too were using
> manual injections as we were experiencing blockages in the tubing of the
> acid pump - probably as we were only using it intermittently (every couple
> of months or so).
>
> Firstly, yes you can clean out the needle. We had some success with heating
> it gently and using a small stiff piece of wire (try the smaller of the two
> tools that you should have for removing the ferrules from the gas bench).
> However, as this points to a problem in acidification, it is probably not
> the final answer.
>
> We tried all sorts of methods of manual injection - the trick is to be able
> to retract the syringe plunger slightly once the acid drops are added to
> avoid the drop of acid on the back of the septum. This is easier said then
> done with phosphoric acid, but using a small gas tight syringe and having
> the acid warm does improve your chances.
>
> We came up with another solution that seems to work. We add the acid in
> small teflon (because it is easy to machine) cups into the sample
> extertainers after loading the carbonate but prior to flushing. We also
> place a small glass "straw" ~1 cm long into the acid to break the surface
> tension (we use sections of the glass capillaries that are used to draw up
> blood). We flush the samples as normal in the gas bench at 72C and simply
> tip the acid after flushing into the exertainer, making sure that it
> interacts with the sample (I had taken to doing this anyway when injecting
> the acid as there is little acid in a large exertainer).
>
> Pros: you never get acid on the septum and you make fewer hole in the septum
> Cons: it is a bit fiddly and occasionally some sample sticks to the bottom
> of the cups
>
> However, results are excellent and it is well worth a try...
>
> Ian
>
> _______________________________________
> Dr Ian Cartwright
> Reader: Groundwater & Stable Isotope Geochemistry
> School of Geosciences
> Monash University
> Clayton 3800, Australia
>
> tel: +61 (0)3 9905-4887 / 4879
> fax: +61 (0)3 9905-4903
>
> e-mail: [log in to unmask]
> http://www.earth.monash.edu.au/~icart
> <http://www.earth.monash.edu.au/~icart>
>
> water, our greatest resource...
> _______________________________________
>
>
>
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]]On
> Behalf Of Andrew Campbell
> Sent: Wednesday, 3 December 2003 3:53 AM
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] Gas Bench Needle
>
>
> 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
> **********************************************
>
>