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ISOGEOCHEM  January 2018

ISOGEOCHEM January 2018

Subject:

Re: estimating values of 13C in a mixture

From:

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

Reply-To:

Stable Isotope Geochemistry <[log in to unmask]>

Date:

Fri, 26 Jan 2018 12:25:07 +0000

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (116 lines)

Shane,

I can sent you a Excel sheet offline that I made a few years ago for the calculation of enriched and natural abundance materials (in liquid form; but this does’t matter).

Isotopes mix linear in natural abundance but if comes to highly enriched values you cannot use a simple mass balance for the calculation of the mix value.

For more information you might have a look in chapter 2 in Carol’s famous book:
Fundamentals of Isotope Geochemistry
Chapter 2.5.3 Mixing
<https://wwwrcamnl.wr.usgs.gov/isoig/isopubs/itchch2.html#2.5.3>

regards,
Robert



> Am 26.01.2018 um 12:38 schrieb Wolfram Meier-Augenstein (pals) <[log in to unmask]>:
> 
> Hi Shane,
>  
>  
> Another caveat would be that stable isotope mass balance equations must be based on atom fractions or mole fractions of the relevant element but not on (compound) mass fractions (or element weight percentages) since delta values are based on (element) isotope ratios.
>  
> Consider this example of d13C of the mixture of equal amounts (mass) of two carbonate minerals of different 13C composition:
>  
> Assume we mix 10 g of aluminium carbonate with 10 g of sodium carbonate.  Constructing a mass balance on the basis of these weights alone will not yield the correct answer not just because aluminium, sodium and oxygen make no contribution to 13C abundance but more importantly because these two carbonates contain different amounts of carbon.
>  
> 1 mole equivalent of Al2[CO3]3 contains 3 atom or mole equivalents of carbon, while 1 mole equivalent of Na2CO3 contains 1 atom or mole equivalent of carbon.
>  
> Therefore, with 10 g of Al2[CO3]3 being 0.0427 mole of Al2[CO3]3 this amount of aluminium carbonate contains 0.1282 mole of C while 10 g of Na2CO3 are equivalent to 0.0943 mole of sodium carbonate which contain 0.0943 mole of C.  A 20 g mixture containing these two carbonates in equal amounts (of 10 g each) contains therefore a total of 0.2225 mole of carbon.  The isotope mass balance therefore reads thus:
>  
> d13C(mix) = [0.1282/0.2225]xd13C(Alcarbonate) + [0.0943/0.2225]xd13C(Nacarbonate)
>  
> Let’s say d13C(Alcarbonate) is -30 ‰ and d13C(Nacarbonate) is -10 ‰, the d13C of the carbonate mixture of equal amounts of Al and Na carbonate would be -21.52 (= -17.28 + -4.24) and not -20 as a purely mass based equation would suggest.
>  
> In your case calculating the d13C of your mixture will depend on how many mole equivalent of C respectively the chosen amounts of compound A (-18) and compound B (+100) will contain.
>  
> At the risk of being accused of shameless self promotion, the recently released second edition of the book “Stable Isotope Forensics” provides several worked-out isotope mass balance equations using FAMES and NAP derivatised amino acids as examples.
>  
>  
> Best,
>  
> Wolfram
>  
> **********************************
> Prof. Dr W Meier-Augenstein, CChem, FRSC
> Stable Isotope Forensics & Analytical Sciences
>  
> School of Pharmacy & Life Sciences
> The Sir Ian Wood Building
> Garthdee Road
> Aberdeen
> AB10 7GJ
>  
> *     [log in to unmask]
>  
> Stable Isotope Forensics book, 2nd edition:
> https://www.wiley.com/en-gb/Stable+Isotope+Forensics%3A+Methods+and+Forensic+Applications+of+Stable+Isotope+Analysis%2C+2nd+Edition-p-9781119080206
>  
>  
>  
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of gerard olack
> Sent: 25 January 2018 21:57
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] estimating values of 13C in a mixture
>  
> HI Shane--
> 
> What John said--but I'll add some caveats....
> 
> This assumes sample is homogeneous after mixing and that both components behave the same during analysis.  If you are playing with carbonates, then you may have to look into what happens with the oxygen and expected 17O.  That usually shouldn't make a big difference unless one sample is also spiked with 18O label.
> 
> take care,
> 
> gerry
> 
>  
> On 1/25/2018 3:31 PM, Shane Crabtree wrote:
> We are trying to estimate the delta value of a mixture of two other materials, one natural abundance 13C (around -18 permil) and the other enriched (+100 permil).
>  
> What is the best way to estimate what the delta value would be after mixing?
>  
> Shane
>  
> <image001.png>
> Shane Crabtree
> Chief Instrumentation and Information Officer
> 105 Westpark Drive Suite 150
> Brentwood, TN 37027
> Phone: 615.376.5464 Ext. 102
> Fax: 615.376.6384
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-- 
PD Dr. Robert van Geldern
Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) | GeoZentrum Nordbayern
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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