We shake for a minute and then put the vials in an ultrasonic bath for
another minute.
On Apr 24, 2007, at 7:27 AM, Anthony Aufdenkampe wrote:
> Matheus,
> I'll echo everyone's advice to vigorously shake a sample after
> acidification. The gas exchange is quite slow and depends on air-water
> interface surface area and turbulence in the water. Therefore,
> reaching
> equilibrium between water and headspace in a small vial will take
> hours (up
> to 24 hrs) in the absense of shaking.
> For my post-doctoral work with river waters I manually equilibrated
> 30 mL of water with 30 mL of headspace in a 60 mL syringe immediately
> prior
> to gas injection into a flow through IR detector system (I'm working on
> publishing this). I found that after acidifying I had to very, very
> vigoursly shake the sample for a full 15 seconds to get reproducible
> results
> (i.e. complete gas equilibrium). This is much longer than one would
> naturally shake and I found it best to keep my eye on a watch to make
> sure I
> didn't undershake. On larger samples, we found that it took minutes of
> shaking to come to equilibrium. Using this method, my reproducibility
> was
> typically <3%.
> For this reason, when I finally start playing with a
> Gasbench-DeltaPlus DIC method, I definitely intend to do all the
> acidification and gas equilibration manually prior to loading vials
> into the
> autosampler.
> Last, it might be worth reminding you, given your comment below,
> that alkalinity and DIC are not equilvalent and you should not expect a
> tight fit between the two. In fact the two are mathmatically
> independent
> and if you measure both well you can calculate the other carbonate
> species
> (and also pH).
>
> Anthony
>
> _____________________________________________________________________
> Anthony K. Aufdenkampe, Ph.D.
> Assistant Research Scientist - Isotope & Organic Geochemistry
> Stroud Water Research Center
> 970 Spencer Road
> Avondale, PA 19311
> Tel: 610-268-2153 ext. 263
> Fax 610-268-0490
> http://www.stroudcenter.org/about/aufdenkampe.htm
>
>
> -----Original Message-----
> From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
> Behalf
> Of Matheus Carvalho
> Sent: Monday, April 23, 2007 9:58 PM
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] DIC quantification by Delta XP
>
> First of all, I want to really thank everybody who made a comment on my
> question, I didn't expect to get so nice advices! This list is really
> awesome!
> Now I will consider about the coments and decide what I am going to
> do. I
> will try to use the Gram titration to measure alcalinity and also to
> calculate DIC applying those corrections for Boron at least, and
> compare
> with what I measured with gas bench. I already did the titration (up
> till
> now I did some careless measurements, assuming that the interferences
> from
> atmosphere and others are negligible) but I couldn't see a clear
> correspondence between the alcalinity results and the gas bench
> results. It
> looks to me that gas bench was giving more more realistic results,
> although
> not necessarily precise. I didn't take any formal course on Gram
> titration,
> and I am learning through trial and error, so it is very possible that
> I did
> something wrong.
> Regarding what precision I want, I still didn't decide. What I
> measured was
> "normal" seawater and water from some abandoned tanks here crowded with
> macroalgae. I sometimes think it would be possible to see some change
> in the
> DIC concentration and isotope values in tidal pools, things like that.
> I
> didn't try in the field yet, so I don't have much idea of the
> precision I
> might be satisfied with.
> Again, thanks for all the comments you people sent, I felt like taking
> a
> course!
>
> Matheus C. Carvalho
> PhD student
> Kitasato University - School of Fishery Sciences Japan
>
> --- "Brian N. Popp" <[log in to unmask]> escreveu:
>
>>
>> These are really informative comments by Dave.
>> His comments also reminded me of the paper by McNeil, Matear and
>> Tilbrook (2001 Global Biogeochemical Cycles, v.3 p. 597). These
>> workers used a SOMMA to acidify and sparge a seawater sample,
>> cryogenically trapped the CO2 and analyzed it using a dual inlet. They
>> get good precision for [DIC] and d13C-DIC.
>>
>> However as Dave asks, what kind of precision do you need for your
>> research? That should dictate your method.
>>
>> At 08:33 AM 4/23/2007, you wrote:
>>> Matheus
>>>
>>> DIC concentrations - good question. There are several ways to obtain
>>> DIC concentrations, but the Gas Bench would not be the place to start
>>> unless precision in not you first goal. If you are serious about
>>> precision you will have to take a more formal approach to DIC
>>> measurements.
>>> For us oceanography folks who require the better than 3micromole/kg
>>> precision do this by either closed cell total alkalinity titration,
>>> SOMMA (coulometer), extraction line (Keeling method).
>>> These system bubble or agitate the sample during
>> acidification.
>>>
>>> Some folks are using the OI system and getting decent results - from
>>> my discussions with folks usually no better than ~8micromole/kg and
>>> up to16micromole/kg. I have made several attempts to get a Shimatzu
>>> TOC5000 working, but could not get it better than 10micromole/kg. For
>>> some, perhaps most folks, this is fine. Our early method (late 80's
>>> early 90's) was using the TCD on the EA, but we only got around 3 to
>>> 8micromole/kg precision (similar to the Weiss IR GC method). We moved
>>> on to the coulometer in a manual mode (manual SOMMA type system) in
>>> the mid 90's, then built our own automated system which worked well,
>>> but not for small samples.
>>> Now we have abandoned the coulometer to do DIC and use an IR detector
>>> with a custom built auto front end to get better than 2micromole/kg.
>>> The difference between how our system runs and the OI type systems is
>>> how we control the sample injection and how we standardize the
>>> instrument.
>>>
>>> I am presently working (this summer) on this instrument to run on our
>>> Delta+. Because of the nature of our research we require dual inlet
>>> d13C-DIC precision of better than 0.03 so all of our DIC isotopes are
>>> done using a multi channel continuous flow extraction system to
>>> sparge and capture. We use this system at sea and in the lab for
>>> isotopes and the IR system for concentrations. I know the Gas Bench
>>> can get 0.1 and sometimes better. My hope is to get our IR system to
>>> approach this dual inlet precision.
>>>
>>> To get accurate DIC concentrations you will need to measure several
>>> factors, e.g., volume, temperature, and salinity (if at sea and
>>> cannot use a balance) or mass (if you can use a balance). Your yield
>>> on the Gas Bench will be in several loop injections unless you
>>> by-pass this loop and introduce the whole sample into the GB column
>>> and into the mass spec. This might be a difficult task controlling
>>> tailing. We have struggled a lot with this on our system. We control
>>> the injection during acidification so that tailing is minimized. The
>>> coulometer is more absolute in that you titrate a sample to an end
>>> point and basically do mole counts (a low drift or blank is required
>>> to get high precision). A clean method, except getting the instrument
>>> to behave at sea. As presented in an earlier email, Andrew Dickson's
>>> Handbook http://andrew.ucsd.edu/co2qc/handbook.html is a great place
>>> to start if you are serious about doing
>> DIC concentrations.
>>>
>>> Some thoughts on the matter. Good luck,
>>>
>>> Dave
>>>
>>> At 03:05 PM 4/22/2007, you wrote:
>>>> Hello everybody, I am going to make a question
>> that I
>>>> know it has the risk of being very stupid. Is it possible to
>>>> quantify (or at least estimate) the
>> amount
>>>> of DIC in a water sample, analyzed using a Gas
>> Bench
>>>> and Delta XP, using the chromatogram generated by Isodat as a basis
>>>> (of course, a standard with
>> known
>>>> DIC concentrationi would be measured too, and precautions to use a
>>>> precise sample volume, etc)?
>>>> I am making this question because when running a
>> few
>>>> samples, the difference between the peak height of some samples was
>>>> very marked, which to me suggests
>> the
>>>> possibility of quantification.
>>>>
>>>> Thank you for any help,
>>>>
>>>> Matheus Carvalho
>>>>
>>>> PhD Student
>>>> Kitasato University School of Fisheries Sciences
>>>>
>>>> Matheus C. Carvalho
>>>> PhD student
>>>> Kitasato University - School of Fishery Sciences Japan
>>>>
>>>> __________________________________________________
>>>> Fale com seus amigos de graça com o novo Yahoo!
>> Messenger
>>>> http://br.messenger.yahoo.com/
>>>
>>
>> ***********************************************************
>>> David A. Mucciarone
>>> Stanford University
>>> Dept. of Geological & Environmental Sciences 450 Serra Mall Building
>>> 320, Room 118 Stanford, CA 94305-2115
>>> 650-723-0817 (O) 650-725-2199 (F)
>>
>> http://pangea.stanford.edu/isotope/dam/sil_home.html
>>
>> ***********************************************************
>>
>
>
> Matheus C. Carvalho
> PhD student
> Kitasato University - School of Fishery Sciences Japan
>
> __________________________________________________
> Fale com seus amigos de graça com o novo Yahoo! Messenger
> http://br.messenger.yahoo.com/
>
>
--
*************************************************************
Steve Nelson
Professor
Dept. of Geological Sciences
S-389 ESC
Brigham Young University
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801-422-8688
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George W. Bush: "Decider in Chief"
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**************************************************************
Disclaimer for the feeble-minded: It should be painfully obvious, but
the identification of my affiliation with Brigham Young University does
not imply that the University endorses any political or otherwise
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