Just a couple of quick notes with regards to storing DIC standards:
I have not found the NaHCO3 solid to drift in isotopic composition when
stored over one year at room temperature in a desiccator.
We do not store solutions of DIC standards for more than one month. The
NaHCO3 solutions are not stable UNLESS they are stored in headspace-free
containers. We usually mix up what we will need for a few weeks, then
immediately pour off the solutions into clear VOA vials with low diffusion
butyl-rubber septa lining the caps. (I punch the septa out myself--an $18
sheet of rubber from McMaster-Carr yields about 450 septa. The teflon-lined
silicone septa that normally come with VOA vials leak like crazy!).
Properly stored, solutions of NaHCO3 greater than 1 mg/l C (83.33 uM) last
for more than a month. By that time, we've usually exhausted the vials we
previously prepared, and mix up more solution.
When making solutions for DIC, I purge ultrapure DI water for 20 minutes
with N2 in order to degas CO2 first, then pipette the
less-than-one-month-old stock solution of 1000 ppm C into 1 liter
volumetric flasks to dilute down to the concentrations I will use to set up
the run. I regularly run solutions of 1, 5, 10, 15, 25, and 50 ppm C.
Since NaHCO3 is cheap and readily available, the cost of all this solution
problem (problem solutions?) is mainly labor.
Per Gilles' comments, one can certainly use DOC standards to correct a run
of DIC samples. However, this extends the run time (DOC samples take twice
as long to run as DIC samples on the TIC-TOC), and the issue of comparing
"apples to apples" so to speak has always nudged me towards running DIC
standard solutions when analyzing DIC samples.
I also recommend using the black butyl rubber septa for sample collection.
A quick wash in Alconox and a rinse in DI water is enough to have clean
septa after punching them out. I have not found a supplier, but I would
imagine the cost to be outrageous even if I found one.
Cheers,
Dan
***********************************************
Daniel H. Doctor
Isotope Tracers Group
U.S. Geological Survey
345 Middlefield Rd, MS 434
Menlo Park, CA 94025
tel: 650-329-4544
fax: 650-329-4538
Gilles St-Jean
<[log in to unmask] To: [log in to unmask]
CA> cc:
Sent by: Stable Subject: Re: TOC high standard?
Isotope
Geochemistry
<[log in to unmask]
UVM.EDU>
05/11/2005 06:43
AM
Please respond to
Stable Isotope
Geochemistry
Hi Anthony
We have prepared a heavier standard by mixing an enriched (99 at% for both
13C and 15N, and a separate 99% 13C Glycine ) with a natural abundance
Glycine. We have targeted +25 and are just now making a +8 permil
standard. Both sets are used for EA and DOC for daily normalisations and
yes they are homogeneous after recristalisation. The solution is dried at
50oC and we wind up with about 15g of the stuff in the end. Enough to last
about 10 to 15 thousand analysis. The problem with using DIC is it's very
short shelf life and shifting values, as Daniel mentionned, with
carbonates. We do not use DIC as standards anymore. Since the reaction
for DIC and DOC is pretty much 100% in the TOC Analyser, then a DOC
standard works for both quite well.
The mixing calculations can be done by mass balance or dilution (M1V1 +
M2V2 = M3V3 where M is in permil). I did a similar prep 15 years ago
making a 4L heavy HD water standard from an enriched water. Using the
dilution equation I targeted +15 and got +15.6.
The Glycine was purchased through Isotec which is a Sigma Aldrich company.
I think you can now find the enriched products in the Sigma catalogue.
If you need more info, contact Paul Middlestead at
[log in to unmask] or call him at xt 6839 (main number below).
Gilles
Gilles St-Jean
Chercheur / Research Scientist
Université d'Ottawa / University of Ottawa
Sciences de la Terre / Earth Sciences
140 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5
Tel: 1-613-562-5800 xt 6830 (Bureau / Office)
xt 6839 (Bureau / Office Lab)
xt 6836 (IRMS lab)
Téléc. / Fax: 1-613-562-5192
Courriel / E-mail: [log in to unmask]
Toile / Web: www.isotopes.science.uottawa.ca
_____
De : Stable Isotope Geochemistry [mailto:[log in to unmask]]
De la part de Anthony L. Michaud
Envoyé : 10 mai 2005 12:21
À : [log in to unmask]
Objet : [ISOGEOCHEM] TOC high standard?
We are getting our working standards together for DIC/DOC using an
OI Analytical TOC analyzer coupled to a Delta Plus Advanatage. We’d like to
have a working standard that is somewhere around -5 to +5 permil vs PDB so
that it is close to our TIC values. Do any of the TOC-IRMS users out there
have suggestions on where I might find an ok standard that is so enriched?
Not much info in the archives concerning TOC standards…
Thanks for any help!
Anthony
------------------------------------------------------
Anthony L. Michaud
Physical Sciences F-686
Arizona State University
Tempe, AZ 85287-1404
Tel: 480-727-8033
Fax: 480-965-8102
http://geopig.asu.edu/keck/index.html
***Windsurf Everywhere***
------------------------------------------------------
|
