Gasbench:
Company: Thermo. Link to website. Please note, application notes are available from the company's website in .pdf format.

Overview Literature Analyses Devices Tips Troubleshooting


Overview:
The Gasbench is designed for headspace analysis. It is used for the isotopic analysis of water via equilibration (with CO2 for 18O and with H2 plus catalyst for DH), DIC and carbonates (after acid addition), breath (CO2), air (CO2, O2, N2), potentially DOC (batch mode), etc. A CTC Pal autosampler is used to inject the sampling needle into the vial and a He flow mixes with and pushes some the headspace gas out through a Nafion drying tube and a sampling loop. The sampling loop periodically switches so the that the gas in the sampling loop is directed to a GC, another drying tube, and then the open split to the mass spec for analysis. Please note, if your sample has other volatile components, e.g. small organic compounds, NOx, etc., they may be released into the headspace and interfere with that analysis or potentially the analysis of later runs. You also have to try to prevent water or acid droplets from entering the sampling system.


Read more about it:


Analyses:
18O on water (CO2 equilibration):

DH on water (H2 equilibration with Pt catalyst):

Carbonates (auto acid addition)

DIC

DOC


Devices:
CTC Pal autosampler
Acid Pump
Nafion Drying tube
GC column
Sampling needle


Tips and Tricks:


Troubleshooting:
Some generic trouble shooting tips, aka things you've probably checked already...
1. open split--just make sure lines are positioned properly so you're not sucking in a little air (both std and samples sides). Also make sure lines move smoothly up and down. And that lines to mass spec are not blocked (close off mass spec before taking these out to air).
2. Check readings with dilution on and off too. You can see if the high background is coming mainly from the sample side.
3. Nafion tubing--pre and post GC column. It can collect garbage--but it's a real pain to get in and out of the gasbench without pulling on/breaking other tubing. Cleaning protocol is on the wiki, see Nafion Drying tube [[home|]]and it's good to have a backup piece around just in case. They also can pinch closed or "slide" off capillary connection.
4. Leaking switching valve--just run with sampling tube in a He flushed vial, and see how big the air peaks are. Double check sampling line He flow by sticking the "exhaust" lines from valve into a small bottle of water to see bubbling rate (only one works at a time--or should be working at a time). If need be, follow the valve cleaning protocol (you may have to check Valco website--and look for new seat if needed--basically you'll need to take the top off to get to the seat to clean it, but you don't want to readjust the spring tension, so manual helps)
5. Contaminated sampling line. Disconnect output at gasbench bushing at put the line in a beaker to collect waste--do not have it feeding the nafion tubing, keep He feed in place. Once output line is in the waste jar, stick sampling needle into a sealed Exetainer tube filled with water so needle tip (sample out) is in the water. This will flush line with water. Stick it in to the He filled vial to let dry (maybe a little flush with ethanol will help)--leave it flushing for a long time before reconnecting.