Dear Georges,
I am sorry for the typo. The external reproducibility is < 0.1 per mil for both the isotopes (for carbon it's slightly better, < 0.6 per mil). I didn't notice that I typed % for per mil.
Debajyoti
Debajyoti Paul, Ph.D.
Department of Earth and Environmental Science
One UTSA Circle,
San Antonio, TX 78249
Office Ph # (210)-458-5751
Office Fax #(210)-458-4469
[log in to unmask]
-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Georges L. Paradis
Sent: Monday, June 05, 2006 5:48 PM
To: [log in to unmask]
Subject: Re: [ISOGEOCHEM] calibration TC/EA for O2
Hi Debajyoti,
I don't think one can assess precision of isotope data as a percent since we
are reporting on a relative scale. For example, +/- 0.1 per mil d18O is not
worse for a sample whose true value is 0.5 per mil than it is for a sample
whose true value is 10. per mil. I'm curious to know what your external
reproducibility is in terms of 1 sigma for d18O and d13C for carbonates.
Much thanks,
Georges
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Georges L. Paradis
ICPMS Lab Manager
Department of Earth Science, Marine Science Institute
University of California Santa Barbara
Santa Barbara, CA 93106
805-893-7182
[log in to unmask]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
----- Original Message -----
From: "Debajyoti Paul" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, May 25, 2006 7:31 AM
Subject: Re: [ISOGEOCHEM] calibration TC/EA for O2
> Dear Pier,
> I have been analyzing calcium carbonate samples using Gasbench II-CFIRMS.
> My guess is that others also analyze carbonates using the Gasbench. We do
> not find any correlation (or linearity) between delta values and sample
> size (variable in the range plus minus 200 micrograms). 1 sigma deviation
> (external error) of multiple analyses is < 0.1% for both oxygen and carbon
> isotopes. So any further correction is not required. This is comparable
> with dual inlet precision.
>
> May I ask one more thing? You are right that "the gas introduced at the
> open split in front of the ion source often is named reference gas". Would
> it be correct to call this just the "Monitoring gas" as per your
> suggestion? All the measured (raw) delta values of international standards
> or unknown samples are relative to this "Monitoring gas". Though the
> international standards and samples are treated in the same way, their
> measured delta values are relative to this Monitoring gas (which is passed
> separately into the IRMS). Then we calculate in VPDB or VSMOW scale, based
> on the shift of measured to true delta value (not linear one, the equation
> given by Coplan)of international standards. Therefore, would it be proper
> to refer this as "reference tank gas" instead of "monitoring gas"? It may
> also help to note "international standard reference gas or just standard
> reference gas" to avoid confusion. As long as this is stated in a
> manuscript clearly, it may not be considered !
> to be completely wrong usage of terminology. I just wanted to clarify so
> that I adopt a terminology (in future) in-line with others.
>
>
> Debajyoti Paul, Ph.D.
> University of Texas at San Antonio
>
>
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
> Behalf Of Pier de Groot
> Sent: Thursday, May 25, 2006 12:43 AM
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] calibration TC/EA for O2
>
> Hi Bill and others,
>
> I cannot resist to react on this one... Your description clearly brought
> forward one of the major caveats of single inlet-CF-mass spectrometry:
> non-linearity! Now, there is nothing wrong in applying corrections. But
> determination of a correction (e.g. linear regression) introduces an
> uncertainty which has to be propagated to the final combined uncertainty
> of
> a measurement, and therefore makes the result less precise. Actually I
> cannot recall even one publication mentioning to include such an
> uncertainty
> as mentioned here...!! Since we see very small precisions reported with
> the
> single inlet-CF machines, you bring forward some clear arguments against
> these (indirectly, yes).
>
> Let me give an example - analysis of carbonates: If comparing phosphoric
> acid digestion with double-inlet and single inlet-CF procedures, we see
> with
> the last method generally smaller precisions are reported in literature
> (also if comparing older work, based on double inlet, with newer single
> inlet-CF type of work). If now considering the fact that single inlet MS
> is
> a less precise way of measuring than double inlet MS and that for the
> single
> inlet far smaller sample size is used compared with double inlet, where
> introduction generally of more heterogeneity by the small sample size has
> to
> be considered, how is it possible that single inlet-CF-MS results are
> given
> with smaller precision than for double inlet results?
>
> Moreover, with Bill's description, it also raises questions for solid
> samples and the unavoidable inaccuracy of sample weight - in sense of
> amount
> of element of interest for the isotopic signature and the variation in
> peak
> sizes and shapes (same amount of gas but with clearly flatter and wider
> peak
> will also give different results compared with a very narrow and higher
> peak, following the description by Bill!) - and how far the delta values
> are
> correct as produced in such machines (this counts for all single
> inlet-CF-IRMS set-ups, not only TC/EA). If not aware of this 'amount'
> problem, results may be quite wrong in some cases - how do we know to
> shift
> the right from the wrong here? A nice precision just based on statistics
> does not tell any of the story here for certain. And how can we correct
> for
> an 'unknown' by regression in Bill's example - just be usuming that...???
>
> One other comment I like to give here: the gas introduced at the open
> split
> in front of the ion source often is named reference gas. This is a
> completely incorrect name - this gas is and CANNOT be considered as
> reference. It only serves to monitor the performance of our mass
> spectrometer (to detect/register drift or eventual major MS problems, for
> instance). Monitoring gas would be the correct term here. Using the wrong
> term is seriously wrong, since it suggest something that is not...
> Reference
> materials (preferably indentical in chemical, structural and isotopic
> character to the sample material to be measured) have to pass the complete
> system in exactly the same way as samples do. This monitoring gas does not
> answer any of these requirements.
>
> It is not that I am against these 'integrated' analytical systems - on the
> contrary, I am happy they exist. But we should be more honest and
> realistic
> in what they can do to my opinion. That is why I reacted...
>
> Best wishes,
> Pier.
>
> ****************************************************************
> Delta Isotopes Consultancy
>
> Dr. Pier A. de Groot
> Pastoor Moorkensstraat 16
> 2400 Mol - Achterbos
> Belgium
> Tel. +32 (0)14 326 205
> e-mail: [log in to unmask] or [log in to unmask]
>
> Associate editor for stable isotopes of eEarth on-line magazine
> http://www.electronic-earth.net
>
> Visit my WEB-site about my ³Handbook of Stable Isotope Analytical
> Techniques², with a link to the Elsevier web site on the handbook (marked:
> ŒOrder Now¹):
> http://users.pandora.be/handbook/index.html
> last update: August 15, 2005
> Volume I is now available. Volume II is expected to be available second
> half
> of 2006.
>
> ****************************************************************
> In a World Without Walls or Fences,
> Who Needs Gates, or Windows?
>
> ****************************************************************
>
>
>
>> From: Bill Showers <[log in to unmask]>
>> Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
>> Date: Wed, 24 May 2006 15:21:11 -0400
>> To: <[log in to unmask]>
>> Subject: Re: [ISOGEOCHEM] calibration TC/EA for O2
>>
>> Willi, Bruno, et al.,
>>
>> The size non-linearity of CO is what caused us problems when we
>> started using the TCEA several years ago. We worked with Hairigh
>> Avak at Bremen who helped us with this technical issue. Basically
>> with liquids that are injected with an autosampler and a Hamilton
>> micro-syringe you can inject about the same size sample every time
>> into the TCEA and size linearity is not much of an issue between
>> samples and standards. But with solids you can not weigh out exactly
>> the same amount of oxygen in every sample, so your CO peaks from
>> solid samples will encompass a range of sizes.
>>
>> To get size linearity with CO, Hairigh had us basically detune the
>> Delta to achieve maximum linearity. This is best accomplished on our
>> system by backing off on the extraction potential and then tuning
>> everything else back up. Maximum sensitivity for us is ~5.8
>> extraction (out of 10), maximum linearity for CO is ~5.05 out of 10
>> on the extraction setting. We detune for for CO and O2, and have
>> <0.1 per mil change between ~1-6 volts.
>>
>> With a new filament and a cleaned source we can get good linearity
>> for CO between 0.5 to 7 volts, but all solid samples need to be
>> within this range to get good results. We then use tripicates of 3-4
>> known isotopic standards that encompass the isotopic range of the
>> samples we are running to calibrate each run for the differences in
>> slope for the isotopic response changes (with CF there is not a 1:1
>> isotopic relationship between accepted isotopic values and measured
>> values for standards due to instrument effects. This linear
>> correction then needs to be applied to the samples for each run). I
>> am not sure how you would correct for size and isotopic
>> non-linearities in the same sample run. I guess you would have to
>> run low, medium and high isotopic standards at small, medium and
>> large sizes and then have a multi-variate regression correction?
>>
>> Detuning the extraction potential does decrease sensitivity, so there
>> is a tradeoff. Then there is the issue of what standards to use and
>> what is the accepted isotopic value of these international
>> standards. Your corrected sample values can change depending upon
>> what values you use to construct your linear regression (defined vs
>> observed)
>>
>> Since you can not run international standards every day in
>> triplicate, you have to develop internal lab standards which are
>> usually some sort of analytical grade reagent. For CO we like sugars
>> since they pyrolize so nicely, but they also have a limited isotopic
>> range. BaSO4s have low O-18 values and sucrose tends to be on the
>> high side, and then there are plenty of compounds that are in the
>> middle. Soda nitre fertlizers from the Atacoma desert have very high
>> O18 values because of their association with atmospheric deposition
>> and you can order 5-20 lbs of that on line, enough for several
>> careers. Some folks have re-equilibrated reagent grade chemicals
>> with waters of different O-18 compositions to get a wide range of
>> isotopic compositions of the one particular compound they are
>> running. You still have to calibrate that with know standards. But
>> that is another discussion. By detuning for size linearity and using
>> a wide isotopic range of standards that bracket the sample isotopic
>> values, we get consistent values run to run. But we measure size
>> linearity every day and throw out any sample values that fall out of
>> that defined range.
>>
>> Best,
>> Bill
>>
>> At 02:03 PM 5/24/2006, you wrote:
>>> Natalia, another thought...
>>>
>>>
>>> Ohlsson and Wallmark published a paper that presents an algorithm to
>>> mitigate the mass effect on isotope ratio analyses. That is, the
>>> ratio changes as a function of material combusted-- which is why we
>>> are fairly careful about weighing standards precisely. In a previous
>>> life, I modified their algorithm because we found that isotope ratio
>>> dropped as a function of Total N or C combusted. It dropped in a
>>> manner that could be approximated by a first order decay curve. We
>>> never adopted this in the lab because it requires analysis of
>>> standards with a range of masses bracketing the masses of the
>>> samples within every run. However, trials showed that this improved
>>> precision in analysis of standards by as much as an order of
>>> magnitude. If it is important for you to run samples of varying
>>> sizes you might give this method a try.
>>>
>>>
>>>
>>> Reference Ohlsson, K.E., and P.H. Wallmark. (1999) Novel
>>> calibration with correction for drift and non-linear response for
>>> continuous flow isotope ratio mass spectrometry applied to the
>>> determination of (delta notation)15N, total nitrogen, (delta
>>> notation)13C and total carbon in biological material.
>>> The Analyst 124:571-577.
>>>
>>> Good luck
>>>
>>> John
>>>
>>> John B. Cliff, Ph.D.
>>> Research Scientist
>>> Advanced Radioanalytical Chemistry Group
>>> National Security Division
>>> Pacific Northwest National Laboratory
>>> Richland, WA U.S.A.
>>> (509) 373-9003, fax (509) 376-5021
>>> ([log in to unmask])
>>>
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Stable Isotope Geochemistry [mailto:[log in to unmask]]
>>> On Behalf Of Dr. Bruno Glaser
>>> Sent: Tuesday, May 23, 2006 11:00 AM
>>> To: [log in to unmask]
>>> Subject: Re: [ISOGEOCHEM] calibration TC/EA for O2
>>>
>>> Dear Tiziano,
>>>
>>> amount dependence might also be due to the split dilution,
>>> especially from the Conlfo II such effects are known and can only be
>>> avoided when using samples with the same amount of analyte element
>>> or in other words using samples yielding e.g. around 2 V signal
>>> intensity.
>>>
>>> Kind regards
>>>
>>> Bruno
>>>
>>> -----Original Message-----
>>> From: Stable Isotope Geochemistry [mailto:[log in to unmask]]On
>>> Behalf Of Tiziano Boschetti
>>> Sent: Dienstag, 23. Mai 2006 17:31
>>> To: [log in to unmask]
>>> Subject: Re: [ISOGEOCHEM] calibration TC/EA for O2
>>>
>>>
>>> Dear Willi and Natalia,
>>> during the analysis of O-isotope I've noted an increase of the
>>> background mass 30 (14N16O, 12C18O), usually the twice of 28.
>>> Probably this could be due to the low purity of CO-reference gas
>>> (4.7 grade), in fact I've also noted an increase of the 32 mass
>>> signal (impurity of oxygen in CO?).
>>> Low Purity of reference CO-gas could be resolved with a point-of-use
>>> gas filtration or gas purifier (
>>> http://www.alltechweb.com/productinfo/technical/datasheets/4001u.pdf
>>> http://www.pall.com/microe_26234.asp?level1=0 ) What do you think?
>>> Ciao!
>>> *****
>>> Tiziano Boschetti
>>> University of Parma, Italy
>>>
>>> *****
>>> ----- Original Message -----
>>> From: Willi A. Brand
>>> To: [log in to unmask]
>>> Sent: Tuesday, May 23, 2006 2:57 PM
>>> Subject: Re: [ISOGEOCHEM] calibration TC/EA for O2
>>>
>>>
>>> Dear Natalia,
>>> I have two comments to your question.
>>> 1. With a perfectly tuned ion source (perfect linearity for CO2 and N2)
>>> we
>>> very consistently see a dependence of the 30/28 ratio upon signal size.
>>> It
>>> is surprizingly constant at +0.3 per mill / Volt (1V = 3 nA 28). We
>>> routinely correct for this, but we do not know the origin. One
>>> possibility
>>> would be formation of an extra ion current on m/z 30 much like the H3+.
>>> If
>>> small amounts of N2 are present in the reference gas, formation of NO
>>> can
>>> occur on the filament, giving rise to NO+ (m/z 30) during reference
>>> measurement. In this case, the correction would have to be applied to
>>> the
>>> reference gas only. However, we see the same dependence upon signal size
>>> on
>>> the sample peaks.
>>> 2. We generally run our reduction at 1400$B!k(JC (tube-in-tube
>>> arrangement with
>>> the He flow reversal installed) and we adjust the sample size to about 1
>>> mg
>>> Oxygen to generate a larger ion current. We found this necessary in
>>> order to
>>> be somewhat less dependent upon background and memory effects.
>>> Regards Willi
>>>
>>> Sevastyanov wrote:
>>>
>>> Hello!
>>> I am a post-graduate student of V.I. Vernadsky Institute of Geochemistry
>>> and
>>> Analytical Chemistry, Russian Academy of Science. I would like to ask
>>> some
>>> questions about our DeltaptusXP mass spectrometer.
>>> Two organic substances were analyzed for their $B&D(J18$B'0(J values
>>> using
>>> our
>>> pyrolysis EA-IRMS system: cellulose and benzoic acid (the reaction
>>> furnace
>>> is heated to 13500C, silver capsules were used). A various samples
>>> amount
>>> were examined, and our results revealed that there is a dependence of
>>> the
>>> $B&D(J18$B'0(J values upon peak amplitude. These changes are not
>>> great when peak
>>> amplitudes exceed 2 V but increase rapidly when peak amplitudes become
>>> less
>>> than 2 V. Thus, in the range from 2 to 1 V $B&D(J18$B'0(J values
>>> become about 5 $B"s(J
>>> smaller. We believe such phenomenon is not normal and we would like to
>>> know
>>> how this situation may be improved and where this phenomenon comes from?
>>> Where linearity area of our system ends? Is that true, that linearity
>>> bounds
>>> by 2V? If this is so, what is the nature of such phenomenon?
>>>
>>>
>>> Best regards,
>>>
>>>
>>> Natalia Sokolova
>>> post-graduate student
>>> V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry,
>>> Russian Academy of Science
>>> 19, Kosigin st., Moscow, 119991, Russia
>>>
>>>
>>>
>>>
>>>
>>> --
>>> .....................................................................
>>> Willi A. Brand, Stable Isotope Laboratory [log in to unmask]
>>> Max-Planck-Institute for Biogeochemistry (Beutenberg Campus)
>>> Hans-Knoell-Str. 10, 07745 Jena, Germany Tel: +49-3641-576400
>>> P.O.Box 100164, 07701 Jena, Germany Fax: +49-3641-577400
>>> http://www.bgc-jena.mpg.de/
>>> http://www.bgc-jena.mpg.de/service/iso_gas_lab/
>>> .....................................................................
>>> GASIR 2005 in Jena:
>>> http://www.bgc-jena.mpg.de/service/iso_gas_lab/gasir2005/index.shtml
>>> .....................................................................
>>
>> William J. Showers
>> Dept of Marine, Earth & Atm Sciences
>> Box 8208
>> North Carolina State University
>> Raleigh NC 27695
>>
>> For express mail: 1125 Faucette Dr.
>>
>> (919) 515 - 7143 Office
>> (919) 515 - 7802 Fax
>> (919) 515 - 3689 Lab
>> (919) 515 - 7911 Field Lab
>> [log in to unmask]
>>
>
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