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
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|Reinhard Well <[log in to unmask]> |
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|08/03/2009 04:03 AM |
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|[ISOGEOCHEM] Instrumentation for dH2 and d18O in soil water using laser spectroscopy |
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|Stable Isotope Geochemistry <[log in to unmask]> |
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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
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____________________________________________________________
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/
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