Hi Everyone,
Like a lot of stable isotopes labs out there we are also thinking
about buying a laser system. To get a feel about how the LGR and
Picarro systems compare I asked both companies to run our three lab
standards. The d18O values of these standards had been calibrated by
the traditional equilibration method and analyzed by dual inlet mass
spectrometry. What I observed is that for the two freshwater
standards both companies did fairly well (...LGR winning out by a
hair), but for the seawater standard neither did particularly well
(i.e., the LGR value was a bit too light and the Piccaro value a bit
too heavy). For dD the LGR system clearly gave better results. The
Picarro data was too heavy at the heavy end and too light at the light
end, which I suspect was simply due to a calibration problem and not a
problem with the instrument.
What I determined by talking to both companies and from the test
results is this. How you calibrate your instruments is important.
Like in traditional IRMS you need to bracket your samples with
standards that cover the same isotopic range.
Conclusion 2, for the seawater samples that I run on a daily basis
I'll be sticking with the Dual Inlet which has the precision we need.
However, for freshwater samples and "tiny" samples either laser system
should work, although I'm beginning to think that for samples with
large amounts of dissolved organics (e.g., soil water, oil field
brines, bog water) a pre-cleaning step maybe necessary. More
discussion about how this pre-cleaning could be done would be greatly
appreciated.
Take care,
Jennifer
On Aug 6, 2009, at 5:49 AM, Pier de Groot wrote:
> Hi Fred, William and others,
>
> Listening to the discussion on SI analysis with different systems, I
> like to
> bring forward that we have to be careful in what are the 'right'
> isotopic
> values.
> We are used mostly to IRMS systematics, which now is considered by
> many as
> the 'golden standard'. Now with introduction of optical spectroscopy
> we may
> see systematic different isotopic values for the same samples.
> Like William stated: "The LGR gave
> large positive errors, the Picarro gave large negative errors. Only
> the
> TCEA gave reasonable values." My question here is how do you know
> the TCEA
> are the correct values? This probably is given in by the fact that
> always
> samples were measured by TCEA, and now again the same values were
> obtained.
> How are you so sure they are 'the correct' values? The values
> obtained by
> optical spectrometry might be more true (if repeatable, but to my
> knowledge
> they can be very repeatable) eventually.
> We should be careful in stating what is true and what is not.
> Of course the systematic difference in values obtained by different
> analytical systems or procedures is not quite new - remind for
> instance
> about systematic differences between measurements with classical DI
> vs.
> CF-IRMS methods...!
>
> Unfortunately I think that the (erroneous) tendency for the future
> will be
> the comparison of optical spoectrometry (or other new technologies
> to come)
> with IRMS methods as 'correct standard'. We have to consider each
> system
> separately and to to see how we can link the data of different
> systems for
> comparison in a proper way.
>
> Have a nice day (over 30°C here, so that will be good).
> Pier.
>
> ****************************************************************
> Delta Isotopes Consultancy
>
> Dr. Pier A. de Groot
> De Schans 47
> 3945 Ham (Oostham)
> Belgium
> Tel. +32 (0)11 72 77 66
> e-mail: [log in to unmask]
>
>
> Associate editor for stable isotopes of eEarth on-line magazine
> http://www.electronic-earth.net
>
> Head of Isotopes in Geosciences of the European Geoscience Union
> (EGU).
> EGU Home web-site: http://www.copernicus.org/EGU/EGU.html
>
> Scientific Committee member of BASIS (Benelux Association of Stable
> Isotope
> Scientists).
> http://www.basis-online.eu/
>
> Visit the Elsevier WEB-site about my “Handbook of Stable Isotope
> Analytical
> Techniques” Vol-II (published Nov. 6, 2008):
> http://www.elsevierdirect.com/product.jsp?isbn=9780444511157
> and Vol-I (was published Dec. 2004) at:
> http://www.elsevierdirect.com/product.jsp?isbn=9780444511140
>
> ****************************************************************
>
>
>> From: Fred Leaney <[log in to unmask]>
>> Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
>> Date: Wed, 5 Aug 2009 09:30:54 +1000
>> To: <[log in to unmask]>
>> Conversation: [ISOGEOCHEM] Instrumentation for dH2 and d18O in soil
>> water
>> using laser spectroscopy
>> Subject: Re: [ISOGEOCHEM] Instrumentation for dH2 and d18O in soil
>> water using
>> laser spectroscopy
>>
>> Dear Reinhard and William,
>>
>> I'm hoping this may help with your decision making.. We have been
>> analysing
>> dH2 and dO-18 extracted from soils and plant stems for 20 years or so
>> primarily as a way of determining plant water sources.
>>
>> Initially, we used azeotropic distillation of the water using
>> toluene as
>> described by Revesz and Woods 1990 and then changed to using
>> kerosene (av gas)
>> as the solvent. Kerosene is safer to use than toluene and changes the
>> procedure slightly from an azeotrpic extraction to something more
>> like "the
>> kerosene acting as a "carrier" to get the water out".. but gives
>> the same
>> result 100% of the water removed and hence no fractionation. The
>> extracted
>> water is purified by adding parafin wax to the sample in a closed
>> container,
>> melting the wax, shaking and letting the wax reharden (the non-
>> polar traces of
>> solvent are trapped theoretically in the wax leaving pure water for
>> analysis.
>> We have found that water thus extracted can be analysed using IRMS
>> for O-18
>> via the automated CO2-water exchange methodology but not via the H2-
>> water
>> exchange because the Pt catalyst becomes poisoned (because even
>> small traces
>> of solvent poison left after parafin wax treatment poison the
>> catalyst). Up
>> until recently (and even now), we use our manual system for dH2
>> analysis of
>> extracted water whereby H2 is generated by passing water over
>> heated uranium
>> (ie reduction method). This method works for dH2 analysis but is
>> quite time
>> consuming.
>>
>> We purchased an LGR analyser a year or so ago and have recently
>> been running
>> comparisons of analyses using exchange (IRMS), reduction (IRMS) and
>> optical
>> laser LGR methodology. So far, we seem to get reasonable results
>> using the LGR
>> for water extracted from soil but not so for water extracted from
>> plant twigs.
>> Our comparisons are continuing and we are hoping to write up these
>> tests over
>> the next few months.
>>
>> Cheers for now,
>>
>> Fred
>>
>>
>>
>>
>> Fred Leaney Manager, Isotope Analytical Service
>> Ph 61883038728, Fax 61883038750
>>
>> Postal Address CSIRO Land and Water
>> PMB2 Glen Osmond, SA 5064
>>
>> Road Address CSIRO Land and Water
>> Gate 5, Waite Rd.
>> Urrbrae, SA 5064
>>
>>
>> -----Original Message-----
>> From: Stable Isotope Geochemistry [mailto:[log in to unmask]]
>> On Behalf
>> Of William Rugh US EPA
>> Sent: Tuesday, 4 August 2009 10:20 PM
>> To: [log in to unmask]
>> Subject: Re: [ISOGEOCHEM] Instrumentation for dH2 and d18O in soil
>> water using
>> laser spectroscopy
>>
>> Hello Reinhard,
>> Our lab has run extracted water from soil and several species of
>> tree's. We have only recently run across some obvious interference
>> problems with 4 particular Alder tree extracts. Different trees,
>> different collection times, and different processing times, but all
>> with
>> a very characteristic interference pattern in the IR Spectra. It
>> makes
>> me worry about effects that may be small enough where data is still
>> credible, but wrong. One of these samples were run by pyrolysis, and
>> also on a Picarro, (having originally been run on an LGR). The LGR
>> gave
>> large positive errors, the Picarro gave large negative errors.
>> Only the
>> TCEA gave reasonable values.
>> We are in the process of looking at all our raw spectra data to
>> see if signs of interference occur with other extracted waters.
>> Hopefully, we can set criteria that will help us spot critical
>> interference. As it stands, the only credible way to rule out
>> interference is to verify the sample using pyrolysis. We are also
>> interested in extraction techniques, either charcoal or solid phase
>> extraction columns to clean contaminants from the water.
>>
>> I personally believe that availability of the raw spectra data
>> is
>> vital. After all, would any lab accept IR-MS data without
>> verification
>> of baseline, peak shapes and the absence of other peaks at least
>> once or
>> twice during the run? At this time, only LGR provides the saved raw
>> scan data. It's not particularly easy to get at, but at least it is
>> there. LGR's raw data files are in relative transmittance units. I
>> would expect Picarros to be in ring down times if they were
>> available.
>> LGR is more like traditional integrated intensity transmittance loss
>> and Picarro uses CRDS.
>>
>> Communication with other labs at this point is extremely useful.
>> I think I'm one of the more worried about the issue at this point. I
>> would welcome further comments, discussions!
>>
>> William Rugh, Chemist
>> Integrated Stable Isotope Research Facility
>> US EPA, NHEERL
>> Western Ecology Division
>> 200 SW 35th St.
>> Corvallis, OR 97333
>> Office phone: (541) 754-4604
>> Lab phone: (541) 754-4515
>>
>>
>>
>>
>> |------------>
>> | From: |
>> |------------>
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |Reinhard Well <[log in to unmask]>
>> |
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |------------>
>> | To: |
>> |------------>
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> [log in to unmask]
>> |
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |------------>
>> | Date: |
>> |------------>
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |08/03/2009 04:03 AM
>> |
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |------------>
>> | Subject: |
>> |------------>
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |[ISOGEOCHEM] Instrumentation for dH2 and d18O in soil water using
>> laser
>> spectroscopy |
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |------------>
>> | Sent by: |
>> |------------>
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>> |Stable Isotope Geochemistry <[log in to unmask]>
>> |
>>> -----------------------------------------------------------------------------
>>> ---------------------------------------------------------------|
>>
>>
>>
>>
>>
>> Dear all,
>>
>> my insitute is considering to purchase a CRDS instrument in order to
>> analyse liquid water samples from soils and aquifers for dH2 and
>> d18O.
>> To analyse pore water with this technique there seem to be three
>> major
>> aspects:
>>
>> 1. Disturbance from organic compounds in the pore water if extracted
>> liquid water is analysed. The bias from alcohols had been already
>> addressed by Brand et al., RCM 23, 1879-1884. Has anyone checked if
>> soil
>>
>> water (including pore water from organic soils) containing variable
>> amounts of DOC would be feasible with this technique?
>>
>> 2. Using liquid--vapor equilibration and analysing H2O vapor. This
>> has
>> been suggested by Wassenar et al, 2008, EST 2008 42, 9262-9267.
>> However
>> this methods seems to be somewhat difficult as it requires complete
>> tightness of flexible enclosures for equilibrating soil or sediment
>> samples. We are also wondering if analysis of the equilibration
>> bags can
>>
>> be done fully automated. However, this technique might be superior
>> since
>>
>> it overcomes the problems from organic contamination.
>>
>> 3. As far as we can see there are two companies (Los Gatos, Picarro)
>> offering instruments for liquid water or water vapor. The question is
>> which one would be preferable for our application?
>>
>> We would greatly appreciate any information to support our decision.
>>
>> Reinhard
>>
>> --
>> ____________________________________________________________
>> PD Dr. Reinhard Well
>> Telefon: +49 (0)531 596 2535
>> Fax: +49 (0)531 596 2599
>> E-Mail:[log in to unmask]
>>
>> Adresse:
>> Johann Heinrich von Thünen-Institut
>> Bundesforschungsinstitut für Ländliche Räume, Wald und Fischerei
>> Institut für Agrarrelevante Klimaforschung
>> Bundesallee 50
>> 38116 Braunschweig
>> Deutschland
>> Web: http://www.vti.bund.de/de/institute/ak/
>>
>> address:
>> Johann Heinrich von Thünen-Institut
>> Federal Research Institute for Rural Areas, Forestry and Fisheries
>> Institute of Agricultural Climate Research
>> Bundesallee 50
>> 38116 Braunschweig
>> Germany
>> Web: http://www.vti.bund.de/en/institutes/ak/
>>
>
Jennifer McKay
Assistant Professor (Senior Research)
College of Oceanic and Atmospheric Sciences
Oregon State University
104 COAS Admin. Building
Corvallis, OR 97331
Office: 541-737-4054
Fax: 541-737-2064
[log in to unmask]
|