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Hi Kinga,

Good you add 'some pieces of the puzzle'. I thought that the value I gave in
my first message was 'just the best one'. Naive, of course, to think things
were that simple.... I had no time to look into the reason of the
difference, so it is good you informed us.

Now there are two reasons my given value is a good one:
1) the reason given by Kinga Revesz (no exchange with a glass wall at
elevated temperature in the on-line method against exchange in the off-line
methods)
2) included cap-delta17O measurement for proper correction on 18O

To avoid exchange of oxygen with glass walls, as is the problem in the
off-line methods as mentioned by Kinga, did anybody try out the Ni-tube
method as is used for oxygen analysis of O-containing organic compounds or
water? This probably will be done the best way by adding 'carbon powder' to
KNO3. I am not sure, but Hg of the Hg(CN)2 might form an amalgam with the Ni
and therefore is not a good idea (?).
Or do I overlook something here? Would be interesting to see the value for
comparison.

Pier.



> "It also must be notified that there is a clear difference between
> 'off-line'
> (CO2, O2) and 'on-line' (CO) methods of roughly 2 - 3 per mil., whatever
> the
> reason. Worrying enough...."
>
> There is an explanation for that difference:
> The off line methods are using high temperature (520 or 800 C), sealed
> tube, carbon combustion  to produce CO2 out of KNO3. At  that temperature,
> there is an isotope exchange between the oxygen of the CO2 and the oxygen
> of the combustion tube (quartz, Vycor, Pyrex).   Therefore, the isotope
> ratio scale factors of the "off line" methods are compressed to 0.3 - 0.7
> that of the scale factor of the on line method.   The oxygen isotopic value
> of the quartz is about 17 per mill, consequently if the oxygen isotope of
> the nitrate around +23 permill (such as it is of the  IAEA N-3), the
> difference between on and off line method would be about -(2-3) per mill.
> However, if the O-18 in nitrate is about +54 per mill, the difference would
> be about -10 per mill, and if the oxygen of the nitrate is -30 per mill,
> the difference would be around +15 per mill.
> This is demonstrated in our paper "Comparison of delta O-18 measurements in
> nitrate by different combustion techniques.  by Revesz and Boelke, Anal.
> Chem., 2002, 74, 5410-5413.
> Cheers:
> Kinga
>
>
>
>
>
>
> Kinga Revesz
> Chemist, Stable Isotope Laboratory
> U.S.Geological Survey
> MS 431
> Reston, VA 20192
> T:703-648-5865
> FAX: 703-648-5274
>
> http://www.isotopes.usgs.gov
>
>
>
>                     Pier de Groot
>                     <pier.de.groot@PA        To:       [log in to unmask]
>                     NDORA.BE>                cc:
>                     Sent by: Stable          Subject:  Re: d 18O  value for
> IAEA-NO-3
>                     Isotope
>                     Geochemistry
>                     <[log in to unmask]
>                     UVM.EDU>
>
>
>                     12/09/2003 09:26
>                     AM
>                     Please respond to
>                     Stable Isotope
>                     Geochemistry
>
>
>
>
>
>
> Moritz and Eddy,
>
> The value I actually gave was the value as given in one of my book chapters
> on standards by Manfred Groening, referring to the Boehlke et al. (2003)
> paper. I looked again in the Boehkle et al (2003) paper, and indeed, a
> number of values is given.
> I am not certain why Manfred selected this particular value (can you react
> yourself on this, Manfred?), but I guess since Boehlke and coworkers took
> into consideration the 'capital delta'17O signature (quoted is the work by
> Greg Michailski and coworkers: Michailski et al. (2002) Anal. Chem., 74:
> 4989-4993) of IAEA-NO-3 (= IAEA-N3) in their determination of the d18O
> value, it was considered the most reliable determination of the d18O for
> that reason!
> It also must be notified that there is a clear difference between
> 'off-line'
> (CO2, O2) and 'on-line' (CO) methods of roughly 2 - 3 per mil., whatever
> the
> reason. Worrying enough....
>
> In any case, we really need to have consensus about the values of standards
> and reference materials. Having a list of values for the same standard or
> reference material is not serving anybody.
> If the given d18O value is the best one (I followed Manfred Groening in
> this) might raise dispute by some. But we have to decide which value we do
> accept! We need to have an isotopic value solidly calibrated and traceable
> to the N-isotope scale - that should be the choice. Otherwise we cannot
> compare with each other and may bias our interpretations.
>
> Pier.
>
>
>> Eddy,
>>
>> The Boehlke paper is indeed the latest report on d18O of IAEA-N3. But be
>> aware that there are quite a number of other (lower) values reported (in
>> parts compiled in the Boehlke paper).
>>
>> Moritz
>>
>>
>> On Tuesday, December 9, 2003, at 05:16  AM, eminet wrote:
>>
>>> Dear list members,
>>> Has anyone of you a d18O value for the reference IAEA-NO-3 (for which
>>> d15N=4.7)?
>>> Thanks,
>>> Eddy
>>>
>>> Eddy Minet
>>> Centre for the Environment
>>> Trinity College Dublin
>>> Dublin 2 (Ireland)
>>> e-mail: [log in to unmask]
>>> tel: +353(0)1 608 2403
>>> mobile: +353(0)86 827 4921
>>>
>>>
>> Moritz F. Lehmann
>> Department of Geosciences
>> Princeton University
>> Guyot Hall
>> Princeton, NJ 08544
>> phone: (609) 258-7544
>> fax: (609) 258-0796         e-mail: [log in to unmask]
>>
>>
>
>