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ISOGEOCHEM  August 2013

ISOGEOCHEM August 2013

Subject:

Re: running carbonates with Gas Bench II, Delta Plus XL

From:

"Geldern, Robert van" <[log in to unmask]>

Reply-To:

Stable Isotope Geochemistry <[log in to unmask]>

Date:

Sat, 24 Aug 2013 10:46:18 +0000

Content-Type:

text/plain

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Hi Paul,

you will not need the Delta V. If we are taking about pure carbonate samples the typical sample volume is in the range of 150 to 300ug, depending on your exact instrument and sensitivity. On our Delta plus XP we use 180ug for carbonate standards (NBS 19 or similar). That give about 5 to 7 Volt, more than enough. I think the XL should not be so different, except for the 12V limit. If your sample material has less than 10% carbonate is get a bit tricky as your need sample amount increases exponentially (for zero carbonate in the sample the sample amount goes to infinity). 

For oxygen isotopes stable temperature is essential. You can run at any temperature as long as standards and samples are reacted at the same temperature. We run our at 25°C but it will take up to 20h to react the samples (or even longer). We only do that because I also run DIC of water samples on the tray and it just takes too long to cool and heat every day. For carbonates only I would suggest to set the temperature of the tray to 70°C, reaction will be finished within less than an hour.

Weigh in your carbonates with a microbalance if available. We put the carbonate powder on a small piece of weighing paper folded in the middle so that it can go inside the exetainer vial. Then take it carefully with a tweezer, hold the vial in a horizontal position, bring the paper with the sample in and turn it 90° so the carbonate falls directly to the bottom. Flush the exetainer with He (5min at 100ml/min flow). You can put the acid also in vial and can heat it up to 70° in one of the right, unused positions of the tray. Take a disposable syringe (1ml or 5mL) and inject a few drops acid in every vial. We do that in the middle of the septa as our sampling needle goes through the septa off-center. Check on your machine. Make sure to pull back the plunger a bit before you pull out the needle so that no acid drop sticks to the lower side of the septa!
We also Vortex every vial for a few seconds to bring all carbonate powder to the acid, but this might be not necessary at 70°C as the acid is not so viscous. Forget about the acid pump delivers with the Gasbench, do it by hand.

If you have to dilute your signal (I can see no reason why you want to do that) you can adjust the height of the sample open split inside the gasbench. It is described in the manual under breath gas analysis. You can adjust the height of the sniffing capillary so that it does not "see" so much CO2 if you bring her a bit up. There are two screws on the pneumatic lifter. Why do want to run 1mg? Isn't it possible to homogenize the sample and take a representative aliquot? If you have to complete 1000ug  the sample you might also reduce the ion source sensitivity by lowering the electron voltage ( as typically do for hydrogen analysis to reduce H3 production)? You might also play around a bit with the helium carrier flow. Increased pressure will cause a higher flow in the whole GB system (make sure not too high...) and will lower your signal.

If you have further questions on sample transfer time, methods, time events etc. let me know.

I see no reason why ICP-OES analysis should not work, but we never tried that.

regards,
Robert

A good overview might also give:
Spötl, C. (2011)- Longterm performance of the Gasbench isotope ratio mass spectrometry system for the stable isotope analysis of carbonate microsamples
Rapid Commun. Mass Spectrom. 2011, 25, 1683–1685, DOI: 10.1002/rcm.5037

D. Paul, G. Skrzypek. Assessment of carbonate phosphoric acid analytical technique performed using GasBench II in continuous flow isotope ratio mass spectrometry. Int. J. Mass Spectrom. 2007, 262, 180.

C. Spötl, T. W. Vennemann. Continuous flow isotope ratio mass spectrometric analysis of carbonate minerals. Rapid Commun. Mass Spectrom. 2002, 17, 1004.


Am 24.08.2013 um 02:13 schrieb stableisotopes UCB:

> Everyone:
> 
> I have a request to set up for carbonate stable isotope analysis. We have a Gas Bench II, without trapping and concentration loops, and a Delta Plus XL available with the possibility of using a Delta V if necessary.  I have not analyzed carbonates before.  Samples will probably be in the 1mg size range.  It seems that a good starting place would be to use manually added phosphoric acid to the carbonate sample in flushed Exetainers.   However, this would appear to generate about 2% v/v CO2 in the Exetainer head space, when out Delta Plus XL saturates at about 0.3% v/v.  Can we dilute with the Gas Bench?
> 
> I am also curious if the residual acidified sample can be used for ICP-OES analysis of Mg, Ca, Mn, Fe and Sr.  Since this is not typically done I assume there is a problem with analyzing samples in a phosphoric acid matrix.  Any information anyone has would be helpful.  This later question on ICP is also being sent to the Plasmachem list, apologies for cross posting.
> 
> Does anyone have recommendations on procedures for this analysis? Any advice and/or literature on the subject would be useful.
> 
> Thanks in advance, Paul Brooks.
> 
> -- 
> Mr. Paul D. Brooks, Spectroscopist,
> http://ib.berkeley.edu/groups/biogeochemistry/
> Dept. Integrative Biology MC3140
> 1005 Valley Live Sceince Building,
> UC Berkeley, CA 94720-3140.
> 
> [log in to unmask]
> Phone: 510-643-1748
> FAX:   510-643-1749

-- 
Dr. Robert van Geldern
GeoZentrum Nordbayern
Applied Geosciences
University of Erlangen-Nuremberg
Schlossgarten 5
91054 Erlangen, Germany

[log in to unmask]
www.gzn.uni-erlangen.de
fon: +49-9131-85-22514
fax: +49-9131-85-29294
room: O 2.112 (office)

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