Everyone,
With discussion on low N and C samples I think it worth mentioning the
dual mixing model for correction small samples, listed below and in the
Isogeochem archives. With all EA systems I have experience with, at some
stage the 15N delta values decrease as the sample gets smaller, and this
dual mixing model corrects well for this. It is possible that some of
the noise in small samples for 15N that others have described might be
improved using this method.
Paul Brooks.
> *Subject:* Re: How to analyze 15N and 13C in small amount of sample?
> *From:* stableisotopes <[log in to unmask]
> <http://list.uvm.edu/cgi-bin/wa?LOGON=A2%3Dind0807%26L%3DISOGEOCHEM%26P%3DR3652>>
>
> *Reply-To:* Stable Isotope Geochemistry <[log in to unmask]
> <http://list.uvm.edu/cgi-bin/wa?LOGON=A2%3Dind0807%26L%3DISOGEOCHEM%26P%3DR3652>>
>
> *Date:* Mon, 7 Jul 2008 08:55:16 -0700
> *Content-Type:* text/plain
> *Parts/Attachments:*
> Parts/Attachments
>
> text/plain
> <http://list.uvm.edu/cgi-bin/wa?A3=ind0807&L=ISOGEOCHEM&E=7bit&P=142633&B=--&T=text%2Fplain;%20charset=ISO-8859-1>
> (184 lines)
>
>
> Ruben,
>
> There has been some discussion on Isogeochem on this before, see the
> post I copied in from the archives below. You can also search the
> archives with serach terms like "linearity correction". For low N the
> Application Flas report No. G29 below is very useful. Hope this helps,
>
> Paul Brooks..
>
>
>
> Content-Type: text/html
> The Finnigan MAT Application Flash report No. G29 along with many
> other very useful application reports are available as a PDF from
> http://cis.thermo-bremen.com/cis/cis_id_2_11. However, to download it
> requires a Finnigan Customer Information Service (CIS) account and
> password. Email me if you would like me to send a copy.
>
> More recent Finnigan Applications are now available to anyone at the
> following site:
> http://www.thermo.com/com/cda/products/product_application_list/1,1062,10122197,00.html.
>
> I would second Paul's suggestion to use the Avak and Fry method to
> correcting for sample size related non-linearities due to "blanks". We
> use this approach for both carbon and nitrogen to dramatically improve
> our precision for small samples.
>
> Cheers, Anthony
>
> _____________________________________________________________________
> Anthony K. Aufdenkampe, Ph.D.
> Assistant Research Scientist - Organic & Isotope Geochemistry
> Stroud Water Research Center
> 970 Spencer Road, Avondale, PA 19311
> Tel: 610-268-2153 ext. 263, Fax 610-268-0490
> http://www.stroudcenter.org/about/aufdenkampe.htm
>
>
> ------------------------------------------------------------------------
> *From:* Stable Isotope Geochemistry [mailto:[log in to unmask]
> <http://list.uvm.edu/cgi-bin/wa?LOGON=A3%3Dind0606%26L%3DISOGEOCHEM%26E%3Dquoted-printable%26P%3D570356%26B%3D------%253D_NextPart_000_004F_01C69BCD.D8661ED0%26T%3Dtext%252Fhtml%3B%2520charset%3Dus-ascii>]
> *On Behalf Of *Paul Brooks
> *Sent:* Thursday, June 29, 2006 7:06 PM
> *To:* [log in to unmask]
> <http://list.uvm.edu/cgi-bin/wa?LOGON=A3%3Dind0606%26L%3DISOGEOCHEM%26E%3Dquoted-printable%26P%3D570356%26B%3D------%253D_NextPart_000_004F_01C69BCD.D8661ED0%26T%3Dtext%252Fhtml%3B%2520charset%3Dus-ascii>
> *Subject:* Re: [ISOGEOCHEM] Nitrogen mass dependance
>
> Non linearity for 15N vs. samples size and methods of running standards
> to calibrate and adjust for this are described in detail in:
>
> "Finnigan MAT Applion Flash Report No. G 29 by H. Avak and B. Fry.
>
> I am not sure how to get a copy of this, I could FAX you one but the
> print is rather small in places so it would not FAX well.
>
>
> The method of correction is also described in "Fry, Brian et al. 1992.
> Automated Analysis of System for Coupled d13C and d13N Measurements.
> Anal. Chem. 1992, 64, 288-291.
>
>
> We use a spreadsheet that adjusts for non-linearity with the output of a
> Europa sceintific 2020 system. It is can be down loaded at with
> instructions on how to use at:
> http://ib.berkeley.edu/groups/biogeochemistry/downloads.php see the
> section "_Elemental Analyzer non-linearity corrections_ ".
>
> The above spreadsheet does not adjust for drift between standards during
> an analysis, which the Europa software does automatically. Several
> drift methods are described on the spreadsheet in the section "_Drift
> Correction Spreadsheets_". In the spreadsheet " Generic Template
> Berkeley 1.00
> <http://ib.berkeley.edu/groups/biogeochemistry/downloads/generic_template_01.zip>"
> pages "smooth 1 std drift" and "p2p 1 std" describe a smooth curve and a
> peak to peak method of drift correcting between standards.
>
> Hope this helps, Paul Brooks.
>
>
[log in to unmask] wrote:
> Hello Daniel,
>
> Here in Lyon we have tried to go down in sample sizes for 13C pollen
> analyses with our Eurovector EA-IsoPrime system. We managed to get
> reliable numbers (SD = 0.2permil) for sample sizes between 2 and 45
> micrograms of pollen which contains about 40%C. The system seems to be
> able to handle that amount of material for pollen analyses.
> The problem you'll be facing with very small samples is homogeneity of
> your aliquote. We did another funny experiment with our EA-IRMS
> system analysing wood sample which we did not griund very finely. We
> first measured five 100 micrograms aliquots of our wood for 13C and
> got SD=0.44permil which is rather high for that kind of experiment. We
> then took the same sample and we weighed five aliquotes of 1.2
> milligrams, measured them using our diluter system and then got
> SD=0.07permil. Obviously there, "small" was not "beautiful".
> I also presented results at the last JESIUM meeting dealing with that
> aspect for small, single fossil carbonate analyses where I showed that
> going down in sample sizes, the increase in SD was due to
> heterogeneities of the sample rather than analytical deterioration. So
> my advice is to be careful with the interpretation of your data from
> very small aliquotes. A suggestion, if it is possible, would be to
> first test the homogeneity of your sample with amphipods which are not
> endangered where you have plenty of material to play with.
> Regarding the reference material sizes, you'll be facing the same
> problem depending on what kind of reference material you use. Of
> course running calibrated material the same way as samples is always
> good analytical practice.Nevertheless our experience with both our
> IsoPrime systems is that they can cope rather well with linearity
> variations both in DI or CF mode even when running small beam
> sizes down to 0.5-1nA. That could give you a bit of latitude for the
> reference material amounts.
> You can contact me off the list for further discussions.
> Hope this helps.
>
> Best regards,
> -----------------------------------------------------
> François FOUREL
>
> UMR CNRS 5125 PEPS
> Université Claude Bernard Lyon 1
> 2 rue Raphaël Dubois - Bât. Géode
> F-69622 VILLEURBANNE Cedex - FRANCE
> Tél : +33 (0) 4 72 44 62 42
> FAX : +33 (0) 4 72 43 35 88
> Email : [log in to unmask]
> Web: http://webpeps.univ-lyon1.fr/
> -----------------------------------------------------
>
>
> Daniel Nelson a écrit :
>> Hi
>> I'm working with an endangered amphipod. I would like to do some
>> isotope analysis (C&N) to look at diet but I can't sacrafice wild
>> individuals. However, I do have a permit to remove walking legs for
>> genetic analysis. One large amphipod (dried) weighs approximately
>> 4.0 mg and one dried leg weighs approximately 0.185 mg. What is the
>> smallest sample weight that can be measured accurately? Can I
>> analyze individual legs, 3 or 4 legs, or doI need to do the whole
>> individual? I realize the whole individual would probably be best
>> but again, I can't sacrafice individuals. Thanks a lot.
>>
>> Dan Nelson
>> MS Student
>> University of Idaho
>>
--
Mr. Paul D. Brooks,
Dept. Integrative Biology MC3140,
3060 Valley Life Sciences Building,
UC Berkeley, 94720-3140.
[log in to unmask]
phone (510)643-1748
FAX (510)643-1749
http://ib.berkeley.edu/groups/biogeochemistry/
|
