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GC-C-IRMS combustion reaction contructionJust 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. TobiasCornell University 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 Hi Robert, 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. Hi Marilyn, 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 & EVENTSUCSC's SIL retires its 15 year-old dual-inlet Optima following a very productive career that generated over 40,000 data points. Two Tsavo Lions In Famed Killings Get Partial Reprieve according to UCSC Graduate Student Justin Yeakel as inteviewed on NPR's All Things Considered. Listen here: 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. 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. |
