Depending on your setup, the pneumatic valve on the oven side might be
inside the oven (pneumatic part outside, plunger extends into oven to
valve seat) or completely outside. It's good to check the flow out the
vent line and the pigtail (bleed out) both with the oven relatively cool
and at temp (after it stabilizes) if you can.
With backflush off, you should see a tiny flow out of the bleed out
lines associated with all the valves (stick end of bleed out capillary
into water and look for bubbles). You should clearly see it on the GC
side. The ones for the He and O2 in the GCC are really slow, and one is
usually faster than the other. You should not see any He flow out the
vent line on the GC side. With the backflush on, you should see flow
out the vent line but not the bleed out line on the GC side, but the
bleed out lines in the GCC will start bubbling with their respective
1. flow out vent line with back flush off--replace seat.
2. no flow out bleed out line (GC side) with backflush off--snug up
fittings a little. You may end up having to replace ferrules.
3. rarely--mainly with valves placed inside GC--the teflon seal around
the shaft may be worn and needs to be replaced. (est. lifetime 2 to 4
4. T inside GC dirty/clogging. Don't use one with the tinest bore. And
no, I couldn't get it to stay in it's holder either.
5. Usually no problems with valves and T's in GCC, unless there was some
noticeable garbage being pushed through the system or a broken capillary
(oops)--but check/snug up a little just in case.
6. Pneumatics OK? Make sure the valves are switching--you will lose a
solenoid on occasion.
7. Other. Dirty inlets, contaminated column, garbage in samples, etc.
8. Oh yeah, connections to the reactors opening up, esp. inside the oven
when using the valco union.
IF you put the backflush on, then you'll see flow out the vent line. It
should be greater than the flow through the GC, e.g. a 1.5 mL/min flow
GC flow rate should give say a 1.8-2+ mL/min out the vent line if the
backflush flow is 0.3+ mL/min. How it will play out in your system will
depend on how the K-factor was set--if the instrument calibrates the
flow itself, you get different numbers with backflush on or off since
you have different back pressures on the GC column. Flow through to the
open split needs to be greater than 0.5 mL/min, the nominal flow into
the mass spec. Not the easiest to measure without putting a union in
the line from the water trap to the open split. Replacing the water
trap with just a capillary line at the end of the reduction reactor will
let you measure the flow there. You shouldn't be losing more than say
10% of the flow out any given bleed out line, may be 20+% total loss.
IF it changes a bit at temp, you could have something opening up-or an
issue with the K-factor. Or you need to fiddle with your setup for
measuring flow rates (and "calibrate" it against flow straight out of
the GC column). Typically I'll eyeball it first, e.g. stick the
capillary into water and watch the bubbles.
GC-C-IRMS combustion reaction contruction
Just out of curiosity and comparison, I would like to gather information on the length of the combustion reaction zone (metal oxide + hot furnace region) for the various commercial GC-C-IRMS systems out there for carbon isotope analysis. (This is not the full length of the combustion reactor tube, only the part with reactant at the high temperature in the furnace). For instance, I am guessing that it's probably something like 8-9 inches for the ThermoFinnigan design. Whatever system you have, I would be grateful for this information. And for good measure, you could also tell me what wire(s) at what dimensions the reactor tube is stuffed with. Since we built our own reactors for years, I lost touch with how the various commercial systems are configured.
Herbert J. Tobias
I still use the original Finnigan heater, but where the Finnigan prebuilt ceramic and wire part would insert, I insert open Alumina tubing (12 " x 1.5 mm od x 1.0 mm id) from Morgan (formerly Bolt) which is used for mechanical support only. Through this alumina liner runs a piece of fused silica with id of 0.45 mm (very important to use a sufficiently large id else the fused silica will shatter as oxidation proceeds... perhaps a volume change as Cu -> CuO?). The wire bundle (spun together on a drill) is one platinum, one nickel and two copper wires, all 0.100 mm diameter. I use 10 cm of this bundle (with minor zig-zag bends about every cm so that it doesn't drop down - yes - that really has happened to me) in the fused silica, and try to place the wires roughly centered in the heater, erring towards the entry end rather than the exit end (it just works better that way for me). I run at 850 C for everything except chlorinated materials or methane (which both run at 960 C). Lifetime of this build is 2 weeks to 3 months (except for running chlorinated materials... a few dozen injections will pretty well poison the wires).
12" x 1.5 mm x 1.0 mm
Carl Johnson WHOI
I've also been in the habit of building my own, with a 6" reaction zone. 2 nickel wires + 1 platinum wire (0.1mm), at 1080C.
Paul Eby, Alberta Research Council
Where do you place connections to your fused silica oxidation tube? At each end of the furnace as for the ceramic tubes? It is of course possible to run the whole distance from backflush tee to open split with a single piece of silica, but Im too mean with my silica tube to try that. Did you have the failures you describe with 0.32 mm silica?
Robert van Hale, New Zealand
I use a continuous piece of fused silica from a Valco 4-way union (connections for GC flow in, flow out to combustion zone, backflush out and O2 trickle in) all the way to the Valco T-union (connections for flow from the combustion zone, flow to the water trap and backflush in). It does require a 2 meter piece of the 0.45 mm fused silica, but guaranteed to be leakfree.
Carl Johnson WHOI
Carl, How do you "fish" the wires through the capillary and have them stay in one place?
Marilyn Fogel, Carnege Institute
We use a "fused silica reactor" similar to Carl's. Yes, the fused silica runs from the GC Interface, through the furnace, into a union inside the oven. This set-up completely eliminates those pesky, leaky unions at the ceramic tube. We still use the ceramic tube as a very necessary support, but the unions simply hold the fused silica in place and do not need to be "air tight".
I get three or four furnaces out of a 25 m length of .45 mm tubing, but I never
need to replace the ceramic tube, which is what I found to be most expensive
and difficult to order.
Also, because it is much less likely to leak, I have found that the wires last
longer, and the peak shape and resolution is FAR better.
I don't know about Carl, but I have a length of 0.25 mm fused silica that I use to push the wires into position. They do need to have a little band to them as Carl said earlier. I have had one or two slide "back" into the oven or slightly "forward" past the furnace. But, this is rare, and it is easy to push the wires
back into place.
Carolyn Colonero, MIT
Fishing them through is done by pushing with a piece of 0.25 mm id x 0.3?? mm od column. As to staying in place, I make a bit of a zigzag of bends along the wire bundle every cm or so (keep the apexes of the zigzags crisp but the angle very shallow or you'll never get the bundle straightened out enough to push it into the capillary). Oh yeah, and cut the end of the bundle with a brand new single edge razor blade against a sheet of paper... it gives a good clean cut that is not deformed so much that it will not go into the 0.450 mm fused silica. A disection scope or magnifying spectacles help too during the intial feeding into the 0.45.
Carl Johnson WHOI
NEWS & EVENTS
UCSC's Stable Isotope Laboratory operations are back to full operations following the Covid-19 shutdown. Please contact the lab if you are interested in our services.
SIL Co-Director Matt McCarthy directed a
weekend program for about 20 Educational Opportunity (EOP) STEM transfer students highlighting the use of stable isotope analyses in phyiscial and biological science inquiry.
UCSC's Stable Isotope Laboratory welcomes new Ocean Sciences faculty member Pratigya Polissar. Dr. Polissar will join the SIL as a co-director
SIL Co-Director Matt McCarthy directed a
weekend program for about 40 Educational Opportunity (EOP) STEM transfer students highlighting the use of stable isotope analyses in phyiscial and biological science inquiry.
SIL Co-director and UCSC Physical and Biological Sciences Dean Paul Koch has been elected 2015 AAAS Fellow for "energetic and innovative leadership in applying stable isotope geochemistry to document and interpret environmental change through the past 65 million years of Earth history.".
Formation of coastal sea ice in North Pacific drives ocean circulation and climate. So indicates evidence published by UCSC scientists Karla Knudson and Christina Ravelo.
Christina Ravelo, Professor of Ocean Sciences at UC Santa Cruz and UCSC Stable Isotope Laboratory co-director, has received the 2013-14 Outstanding
Faculty Award from the Division of Physical and Biological Sciences. The annual award is the division's highest
honor for faculty achievement, recognizing combined excellence in research, teaching, and service.
Long-term human influenced dietary habits of Yosemite National Park black bears explored by UCSC scientist Jack Hopkins, Paul Koch, and colleagues.
SIL Co-Director Paul Koch honored as a Fellow of the California Academy of Sciences. See story here.
Diversity of great white shark diet was shown to be greater than previously thought based on research by UC Santa Cruz colleagues Sora Kim, Paul Koch, and James Estes along with co-author M. Tim Tinker of the U.S. Geological Survey. This work was highlighted in the Los Angeles Times.
SIL Co-Director Paul Koch has been named Dean of the UC Santa Cruz Division of Physical and Biological Sciences.
SIL Co-Director Paul Koch was quoted in the New York Times on research showing that a tiny Paleocene horse Sifrhippus, the first horse, grew even smaller during the Paleocene-Eocene Thermal Maximum climatic warming event.
SIL Co-Director Christina Ravelo has been selected as an American Geophysical Union (AGU) Fellow.
SIL Co-Directors Paul Koch and Jim Zachos's research on Paleocene-Eocene Thermal Maximum (PETM) climatic warming event is featured in an National Geographic article "Earth Before the Ice" in the October 2011 issue.
SIL Co-Director Paul Koch has been appointed Interim Dean of the UC Santa Cruz Division of Physical and Biological Sciences.
SIL co-director Christina Ravelo (Ocean Sciences) sails as co-chief scientist on Integrated Ocean Drilling Project (IODP) Expedition 323 to investigate Bearing Sea Paleoceanography.
SIL co-director Christina Ravelo (Ocean Sciences) gives the 2008 Emiliani Lecture at the American Geophysical Union Meeting in San Francisco on "Lessons from the Pliocene Warm Period and the Onset of Northern Hemisphere Glaciation".
UCSC SIL has been funded by the National Science Foundation for a new Dual-Inlet Isotope Ratio Mass Spectrometer with individual acid drip system for very small calcium carbonate samples.
SIL co-director Jim Zachos (Earth and Planetary Sciences) recieves prestigious Humbolt Research Award. See Humbolt Award for details.
SIL Co-Director Jim Zachos has been selected as an American Geophysical Union (AGU) Fellow.
May 19, 2006: UCSC Stable Isotope Laboratory Symposium
In recognition of the new continuous flow instruments added to the UCSC stable isotope facility a Symposium is being run to highlight the new analytical capabilities.