Dear Zheng-Hua,
Thanks for clarification. Sounds better now...
Pier.
> Dear Pier,
> Like I said, it was not easy to tell the whole story! I am sorry to use the
> word “boiling” to confuse you. You are right, you can not see the acid boiling
> at 120C. Since there is a magnet in the acid bath, it spins fast, make the
> acid look like “boiling”. My point is because the reaction temperature is
> high; the high acid vapor pressure may pose an issue. Let me bring you more
> details: We use >100% acid, and it is cooked overnight at 120 degree C with
> continuous Helium flow vent, so (I assume) there is no water left in the acid,
> and we pump out between samples, the left over water is supposed to be pumped
> out too. I am not familiar with your question about CaO. Since our data come
> out very well, repeatedly. The “CaO” thing may not pose an issue in this
> system.
>
> Zheng-Hua
>
>
>
>> ===== Original Message From Stable Isotope Geochemistry
> <[log in to unmask]> =====
>> Dear Zheng-Hua,
>>
>> Thanks for giving more detail on the changes in method. It is highly
>> appreciated.
>> However, from your statement that your acid boils at 120 degree C, I can
>> conclude you do not use strong phosphoric acid of higher density (say the
>> +100 percent acid), as actually originally used for the calibration of the
>> system (there was discussion on this item years ago, in the early days of
>> isogeochem list - see the archives!). If you use +98 percent acid the
>> boiling point is 158 degree C (reference: Aldrich guide). What means that
>> you are boiling of water if the acid boils (the acid does not really boil
>> itself, but is just releasing boiling water as far as I understand - I do
>> not think (hope) you will have any phosphoric acid vapour; fortunately not
>> because then you were really in problems with risk of attack of your walls
>> of the system or other nasty effects)... and what is the influence on the
>> CO2 from your reaction? How is the control on exchange between this water
>> and CO2, the O in the acid, the O in the CaO left over from reaction... to
>> give some questions! This will introduce quite some more uncertainty in your
>> method.
>> No criticism to you - you do as many others do in applying this system.
>> I just want to bring forward, as triggered by your posting, some of the
>> worries I have... This kind of matters must have their effect on the
>> results, although in general we see these very nice small precisions
>> presented with the results. How comes...???
>>
>> Best regards,
>> Pier.
>>
>>
>>> Dear Pier and others,
>>>
>>> Well, it is a little bit hard to describe all details about the
> modifications
>>> in an email. It would be easier to tell the story with some diagrams. Here
> I
>>> can tell you the main things I did with the original CarboFlo:
>>>
>>> 1) I spared a valve on the CarboFlo to control the Helium gas, so that I
> can
>>> pump out the whole system between samples (to eliminate the memory effect).
>>> 2) Instead, I use a valve as a vent on DeltaS to replace the original vent.
>>> 3) The original LN2 trap (for CO2) was replaced by a two-way stainless
> steel
>>> tube filled with silver wood to increase the CO2 trapped surface.
>>> 4) The Carousel is sealed, so that all system can be pump out to the
>>> background quickly.
>>> 5) Since the original Carousel has some issues, such as, when it spans,
> some
>>> samples can be spread out of the silver tin cap,this may mess up other
>>> samples. A single-ring cap was made to solve this problem.
>>> 6) Since the hardware structure was modified, I had to change the software
> for
>>> the large sample and micro-volume measurement accordingly, such as, the
>>> pumping out time, Slurry and LN2 trap time, pneumatic valve control, etc.
>>>
>>> Since we use 120 degree C reaction temperature, this high temperature
>>> causes the acid boiling. To avoid any acid get into the system, we always
> keep
>>> the Slurry on. I haven't found this is an issue for this modification so
> far.
>>>
>>> Cheers,
>>>
>>> Zheng-Hua
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>> ===== Original Message From Stable Isotope Geochemistry
>>> <[log in to unmask]> =====
>>>> Dear Zheng-Hua,
>>>>
>>>> What were those modifications in hardware and software that reduced your
>>>> memory-effect? This way it does not tell us very much why and how you
>>>> obtained this result. I am interested (and probably some others) to see a
>>>> bit more details...
>>>>
>>>> Regards,
>>>> 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]
>>>>
>>>> Visit my WEB-site about my ³Handbook of Stable Isotope Analytical
>>>> Techniques², including pdf files of an order form and a flyer for
>>>> downloading, at:
>>>> http://users.pandora.be/handbook/index.html
>>>> last update: October 1, 2004
>>>> Volume I is now available. Volume II is expected to be available medio
> 2005.
>>>> ****************************************************************
>>>>
>>>>
>>>>
>>>>
>>>> Dear Bryan,
>>>> You might be interested in knowing something else in addition to GasBench
>>> II
>>>> and GV's MulitFlow Geo.
>>>> Our lab is equipped with a Finnigan CarboFlo device to run large carbonate
>>>> samples (2-4 mg). As you probably know, this device has some memory-effect
>>>> issues, particularly when running small samples. In order to minimize this
>>>> effect, I modified this device a bit both for the hardware and therefore
>>>> software. Now this device runs very well. Here are some numbers you might
>>> want
>>>> to know:
>>>> ---------------------------------------------
>>>> Auto carousel: 39 samples
>>>> Standard Dev.: d13C=0.03 permil, d18O=0.1 permil
>>>> Experiment time: ~30 hours
>>>> Acid volume: ~10 ml
>>>> Reaction temp: 120 degree C
>>>> ----------------------------------------------
>>>> To check the memory effect on the modified CarboFlo, I had used four
>>> carbonate
>>>> standard samples (NBS-18, CHCC, ANU P3, ANU M2), which d13C values range
>>> from
>>>> +2.24 to -10.68 permil, I found the memory-effect is tremendously reduced
>>> to
>>>> almost none at this d13C range, as you can see from d13C standard
> deviation
>>>> above.
>>>>
>>>> Cheers,
>>>>
>>>> Zheng-Hua
>>>>
>>>>
>>>>
>>>>> ===== Original Message From Stable Isotope Geochemistry
>>>> <[log in to unmask]> =====
>>>>> Dear All,
>>>>>
>>>>> We currently have VG-micromass-GV "optima" IRMS at our lab which
>>>>> we have been using for bulk carbon and nitrogen stable isotopes for the
>>>>> past 11 years. For the most part, the instrument has operated
>>>>> exceptionally well, with a few minor exceptions. One thing I don't like
>>>>> is the operating software; I'm not a big lover of OS2, as I wish we had
>>>>> something windows based, as it would certainly make data manipulation
>>>>> easier.
>>>>>
>>>>> Currently we are looking into acquiring a new instrument and I have
>>>>> researched both the DeltaPlus and GV's Isoprime. From those of you who
>>>>> have responded via the ISOGEOCHEM site, there seems to be two camps out
>>>>> there: those who prefer Finnigan instruments and those who prefer GV
>>>>> instruments. It would seem preference may be a function of what
>>>>> instruments people have worked on in the past and feel comfortable with,
>>>>> or what was previously available at a particular lab. Certainly there
>>>>> are features that are different between the two companies, for example
>>>>> the operating software: Isodat NT vs MassLynx, but I don't know how
>>>>> other hardware components(mass spectrometer, EA, GC, and respective
>>>>> carbonate devices) compare.
>>>>>
>>>>> I am particularly interested in the ability to measure carbonates via
>>>>> continuous flow and have heard that ThermoFinnigan's GasBench II
>>>>> operates well for these measurements. I have not heard to much regarding
>>>>> GV's MulitFlow Geo, and am wondering how it stacks up to the other
>>>>> carbonate devices (i.e. Kiel). I know precision drops with the gas
>>>>> benches compared to a Kiel system, but we are not doing paleoclimate
>>>>> work and a drop in precision isn't critical, especially given our
>>>>> research questions. I think GV and ThermoFinnigan both state that
>>>>> precision is about .1permil for carbon and oxygen isotopes via CF. Have
>>>>> any of you run carbonates using the MultiFlow Geo? Can large carbonate
>>>>> samples(500ug - 1500ug) be run on the MultiFlow? I know ThermoFinnigan's
>>>>> Gas Bench has an autodiluter, capable of reducing the signal to the mass
>>>>> spec, but do not know if GV's MultiFlow has this capability? I suspect
>>>>> it does, but would be interested to hear any feedback on the
>>>>> subject........
>>>>>
>>>>> Regards-
>>>>> Bryan Taplin
>>>>>
>>>>> Bryan Taplin
>>>>> Environmental Scientist
>>>>> US Environmental Protection Agency
>>>>> NHEERL- Atlantic Ecology Division
>>>>> 27 Tarzwell Drive
>>>>> Narragansett, RI 02882
>>>>> Tel. (401) 782-9607
>>>>> Fax (401) 782-3030
>>>>
>>>> Dr Zheng-Hua Li
>>>> Senior Research Associate
>>>> 306 G&G Building
>>>> Dept of Earth and Planetary Sciences
>>>> University of Tennessee
>>>> Knoxville, TN 37996
>>>> USA
>>>> Tel: 1-865-974-9622
>>>> Fax: 1-865-974-2368
>>>> http://web.utk.edu/~zli
>>>>
>>>>
>>>
>>>
>
>
|
