Dear All,
Thank you for your interesting replies.
I would still like to know what is the  general 
reproducibility for silver phosphate in your 
labs, regardless the technique you are using to 
measure the values (I am assuming there are few 
remaining fluorination lines out there). You 
could reply to me off-line, but this would be extremely useful for me.

Penny,
Thank you for re-opening the bioaptite group!
However, regarding your suggestion of using NIST 
1486 standard, I'm not sure it could be a 
suitable one. We are adding another complication 
to the picture, which is the pre-treatment 
method. I don't believe there is so far any 
general agreement in the most appropriate 
technique to remove the organic material in 
bones. I think we should go for tooth enamel, and 
probably just for inorganic silver phosphate, to calibrate the instrument.

Gerry, Wolfram, Matt and Francois,
I was aware of the Vennemann et al., and the 
Lecuyer et al papers, but I wasn't of the LaPorte 
et al. one. I heard only of the new strategy for 
the helium upstream described in that article.
I am also calibrating my data with the Tubingen 
standards TU1 and TU2 here, but I am running out 
of them, as I've only a little "inherited" amount.

Lecuyer et al paper is very interesting, but 
nobody has so far produced a standard big enough 
to share among our community (and the same 
problem, by the way, stands for bioapatite CO3 measurments!).

Wolfram, it is not completely true that IEAE is 
not interested. I spoke about this issue with 
Manfred Groening from IAEA at the Jesium 2008 and 
he told me that they haven't the equipment to 
precipitate silver phosphate there, but would be 
happy to help us creating a silver phosphate standard.

Matt,
Although I've used a number of precipitation 
techniques in the past, I also use the Dettmann 
et al., 2001. I'm glad you came up with such a quick method!
I have a three-points calibration approach (TU1, 
TU2 and NBS 120c), running samples at 1450 °C , 
but I am struggling to give NBS 120c an assigned 
value.In fact, there is a recent paper, by 
Chenery et al., JAS 2010, where the authors 
report the average of all the NBS120c values 
reported in literature, regardless the methods 
used. I can count at least twenty papers. That 
mean value is 21.7 ± 0.5. However, in our 
calibration versus VSMOW (i.e. with isotopically 
recognised standards), we also obtain a more 
18O-enriched value, of about 22.40 ± 0.3 (value, 
which is more similar to the one you suggest and 
the 22.58 given in Venneman et al., as fluorinated value).
Could this difference be associated to the fact 
that this in-house standard isn't really a 
standard but a "precipitated (i.e.altered), 
non-meant for isotopes standard"? People are 
using different methods to precipitate Ag3PO4 
from NBS 120c, making that probably incomparable. 
Do we rally need to use NBS 120c at all?

Torsten,
I'm glad you are precipitating new material. I'm 
willing to participate in any inter-laboratory 
comparison, if you wish to involve me.


All the best the all of you. I'm glad I triggered this discussion.

Maura




At 12:46 28/01/2010, you wrote:
>Dear Maura, and others,
>
>Thanks for the references to Vennemann et al. (2002), which (of
>course :) ) I also agree with is a place to start. Having just today
>reduced some results for about 60-odd samples analyzed using the TC-EA
>method as described in that reference, I can confirm that the
>reproducibility we stated still holds true. Given a well-prepared
>column and a leak-tight system, the average precision I obtained for
>those 60 odd samples was 0.21 permil, similar to that for a run we did
>about two months ago that came out to an average of 0.24 permil (both
>1s, samples run in triplicate, plus a bunch of standards throughout
>the run) for the same number of samples analysed (60-odd samples, all
>in triplicate). The preparation method used for samples given in
>Vennemann et al. (2002) was that of Stephan (2000), while that used in
>my lab presently is a method modified after 
>Dettman et al. (2001). TC- EA is the same type 
>as the one I used in the past while still at
>Tübingen - no fancy sample tray nor low-blank autosampler, just the
>standard system which does give us low blanks though when well-serviced.
>
>To add to the use of TU1 and TU2 as scaling references: I sadly no
>longer have any of these left for free distribution, but we are in the
>process of preparing a new batch of standard material with a large
>range of d18O values for our internal use and possibly for
>distribution again...
>
>Have a great time, best regards,
>
>Torsten.
>
>Le 26 janv. 10 à 15:48, Matthew Kohn a écrit :
>
>>Hi Maura,
>>
>>The place I'd start is with Vennemann et al. (2002; Chem Geol) .
>>Basically you *should* have at least 2 points to calibrate
>>accurately. I prefer a low-d18O igneous apatite from the Laramie
>>anorthosite complex, which Ron Frost (University of Wyoming)
>>provided. It was fluorinated by Farquhar et al. (1993; EPSL) for
>>total oxygen, but these apatites have very low OH content, so it's
>>effectively PO4.
>>
>>Yes, NIST-120c contains a lot of other oxygen sources besides PO4,
>>so you need to precipitate Ag3PO4. For example, I actually use it as
>>a standard for analyzing CO3 in phosphates (e.g. Kohn et al., 2005;
>>Geology), although the long-term reproducibility isn't as good as
>>I'd like, for reasons I don't fully understand.
>>
>>Regarding the "best" value for d18O in PO4 in NIST-120c, again I'd
>>consult Vennemann et al. As I recall, the average of all their
>>calibrated analyses was ~22.1‰. I was getting ~22.4‰, though by
>>sealed-tube combustion. And I recall Reese Barrick and Bill Straight
>>telling me they typically got between 22 and 22.5‰ when they were
>>fluorinating. So I prefer a value of ~22.25‰. As far as I know, the
>>21.7‰ that you quote came from a single study (Crowson et al., 1991;
>>Analyt. Chem.), and while it was a good study, it's only 1.
>>
>>For precipitation, I use Dettman et al. (2001), modified by Kohn et
>>al. (2002) [Not surprisingly...].
>>
>>Matt
>>
>>On Jan 26, 2010, at 6:42 AM, Penny Higgins wrote:
>>
>>>Hi Maura (and everyone else),
>>>
>>>We talked about this at the bone diagenesis meeting. Once upon a
>>>time I was trying to organize all of us working with bioapatites to
>>>make steps toward creating a proper set of standards.
>>>
>>>There is another NIST standard out there that is a bioapatite,
>>>though is not calibrated for isotopes. This is NIST 1486 - Cow
>>>Bone. It is used for rare earth elements. I used it recently and
>>>obtained values of approx -8‰ for d13C and approx -13‰ for d18O
>>>(both on the V-PDB scale).
>>>
>>>As there may be extended interest in this topic, I am reminded that
>>>many years ago I created a listserve for those of us working with
>>>bioapatites. It's been quiet for a very long time, but is still
>>>there. If you wish to subscribe, send an email to:
>>>[log in to unmask]
>>>
>>>with the following text in the body of your 
>>>message (add your e- mail address without the 
>>>brackets; e.g. "subscribe bioapatite [log in to unmask] ":
>>>
>>>subscribe bioapatite [your-email-address]
>>>
>>>I'm interested in what bioapatite standards can be prepared as well
>>>and am looking forward to the discussion.
>>>
>>>~Penny
>>>
>>>At 08:03 AM 1/26/2010, you wrote:
>>>>Dear colleagues,
>>>>I would like to pick on your brains out there.
>>>>I believe some of these issues arose a couple of times in the
>>>>past, but I cannot find
>>>>anything in the isogeochem archive. Any hints will be appreciated.
>>>>
>>>>I am curious to know what is the average reproducibility (1s) you
>>>>are
>>>>getting for phosphate oxygen isotope values by means of pyrolysis
>>>>techniques. What do you consider acceptable and what unacceptable in
>>>>your labs?
>>>>
>>>>What kind of standards are you using and what kind of calibration (1
>>>>point, 3-points)? Also, can you see any differences in
>>>>reproducibility
>>>>between pure inorganic commercial Ag3PO4 and Ag3PO4 precipitated
>>>>from
>>>>skeletal material or phosphorite rocks?
>>>>
>>>>I have seen that most people are using NBS 120c, as a 1-point
>>>>calibration, but this is not a standard certified for isotopes.
>>>>Besides,
>>>>it often falls outside the normal range of values for most of the
>>>>mammals skeleton-derived silver phosphate precipitates. On top of
>>>>that,
>>>>this material has to be precipitated before being measured in the
>>>>TC/EA
>>>>or analogues, whilst there are several precipitation techniques
>>>>out there.
>>>>How can we assess the accuracy of our results if each of us has to
>>>>precipitate its own in-house NBS 120c "standard"? Are they
>>>>supposed to
>>>>be comparable?
>>>>
>>>>I imagine someone will reply that the value of the in-house standard
>>>>should be assessed by calibrating the ref-gas and the NBS 120c by
>>>>comparison with other internationally recognized standards, but
>>>>how do
>>>>we deal with the matrix effect? We carried out that test anyway, but
>>>>results for NBS 120c are 18O-enriched compared to the most commonly
>>>>reported values of 21.7 per mil.
>>>>
>>>>Finally, what precipitation method are you routinely using?
>>>>
>>>>I'm really struggling with these issues.
>>>>
>>>>Thank you. Maura
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>Maura Pellegrini, PhD
>>>>
>>>>Post Doctoral Research Associate
>>>>Division of Archaeological, Geographical and Environmental Sciences
>>>>School of Life Sciences, University of Bradford
>>>>Richmond Road, Bradford, West Yorkshire
>>>>BD7 1PD
>>>>United Kingdom
>>>>
>>>>Tel: +44 1274 236907
>>>>Fax: +44 1274 235190
>>>>email: [log in to unmask]
>>>>Website: 
>>>>http://www.brad.ac.uk/AGES/Research/index.php/Staff/DrMauraPellegrini
>>>
>>>*******************************************************************
>>>                     Dr. Pennilyn Higgins
>>>                      Research Associate
>>>
>>>                           "SIREAL"
>>>Stable Isotope Ratios in the Environment Analytical Laboratory
>>>
>>>       Department of Earth and Environmental Sciences
>>>       University of Rochester
>>>       227 Hutchison Hall
>>>       Rochester, NY 14627
>>>
>>>                  [log in to unmask]
>>>
>>>Office: 209b Hutchison Hall               Lab: 209 Hutchison Hall
>>>Voice : (585) 275-0601              Outer lab: (585) 273-1405
>>>FAX   : (585) 244-5689              Inner lab: (585) 273-1397
>>>
>>>         http://www.earth.rochester.edu/SIREAL/index.html
>>>*******************************************************************
>>
>>**************************************************
>>Dr. Matthew J. Kohn, Associate Professor
>>Department of Geosciences
>>Boise State University
>>1910 University Dr.; MS1535
>>Boise, ID 83725-1535
>>[log in to unmask]
>>phone: (208)-426-2757   fax: (208)-426-4061
>>**************************************************
>
>Torsten Vennemann
>Vice-Doyen, recherche
>Institut de Minéralogie et Géochimie
>Université de Lausanne
>CH-1015 Lausanne
>
>Tel: +41-21-692-4464 / -3510
>Fax: +41-21-692-4305
>[log in to unmask]