Thanks for your reply Robert.

The problem with using an off-line internal standard
is that while you might be correcting for changing
mass bias, you can't correct for changes in ablation
efficiency due to variations in the material
structure. Alas.

As for clogging the instrument - I suspect I need to
talk to people who have actually tried this - maybe
people who do tree-ring analysis by LA-ICP-MS.

Anyway - thanks again.

Cheers,

Dan

--- Robert Clough <[log in to unmask]> wrote:

> Hi Dan
> A better forum for your question would be the
> plasmachem list, which deals with all things related
> to plasmaspectrochemistry and more. The link to join
> is
>
http://listserv.syr.edu/scripts/wa.exe?SUBED1=plasmachem-l&A=1
> or google for plasmachem list.
> 
> A basic answer to your questions.
> 1) depends on the nature of the organic material,
> the ablation conditions and instrumental setup. The
> cones are the most likely area to clog up and maybe
> the extraction lens. The only way to find out is to
> try. Cones are easy to clean, ultrasonication in
> water usually does the trick, see the plasmachem
> archives for other methods using 'stronger'
> solvents. Lens cleaning requires more knowledge
> either from an in house expert or the manufacturers
> engineers, once learnt from them you may be able to
> clean lenses yourself.
> 2) C on a quad ICP-MS is not really feasible due to
> air entrained in the plasma. Having said that you
> may be able to monitor 13 C depending on the
> instrument although expect high background levels. S
> is similar, due to O2 polyatomic interferences,
> although 33S or 34 S may again be possible.
> When normalising to another element in the sample
> you have to have 100% homogeneity for this element
> or biased results occur. Another approach is to tee
> in a desolvated internal standard into the transfer
> line post ablation.
> Yours
> Rob
> 
> 
> ________________________________________
> From: Stable Isotope Geochemistry
> [[log in to unmask]] On Behalf Of Dan Sinclair
> [[log in to unmask]]
> Sent: 23 April 2008 11:01
> To: [log in to unmask]
> Subject: [ISOGEOCHEM] Laser-ablation mass
> spectrometry of organic matrices
> 
> Hi All,
> 
> Does anyone have experience with laser-ablation mass
> spectrometery (specifically ICP-MS) on organic
> samples? I'm considering attempting some analyses on
> antipatharian coral skeletons, which are made from
> gorgonin - a tough chitinous organic material.
> 
> I have two questions:
> 
> 1) Does laser-ablating organic material create
> problems for the instrument (such as contamination
> of
> the instrument, major shifts in sensitivity, and/or
> 'gumming up' of the plates and cones and detectors
> and
> such)? If so, is there an effective way of
> 'cleaning'
> the instrument after such analyses.
> 
> 2) I'm used to CaCO3 analyses where one normalises
> all
> analyses to calcium (to correct for fluctuations in
> ablation efficiency). What would one do for an
> organic
> material? I don't know if there is an effective way
> of
> monitoring C on quadrapole ICP-MS. Maybe there is
> another component of the material that could be
> monitored to normalise ablation (S perhaps?)
> 
> I'd be grateful for any help or advice!
> 
> Cheers,
> 
> Dan Sinclair
> 
> 
> 
> Scottish Association for Marine Sciences
> Dunstaffnage Marine Laboratories
> Oban, Argyll PA37 1QA
> Scotland
> 
> Ph: +44 (0)1631 559 412
> Fax: +44 (0)1631 559 001
> 
> http://www.sams.ac.uk/research/sams-scientific-staff
> http://www.ig.utexas.edu/people/staff/dan/
> 
> 
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> y7mail email address. www.yahoo7.com.au/y7mail
> 



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