g.c. for CO2, N2O, perhaps CH4

[yankee]

Hello GC Forum,

I am currently shopping for a g.c. that can perform both CO2 and N2O from a single injection, preferably. In the past, I've used a TCD and ECD, respectively, for these analyses. Varian has suggested using a helium ionization detector, with which (they say) I can also get CH4 (which occasionally is of interest to me, but isn't a financial priority right now). I have never heard of using a HID for N2O, and I can't find any references in the global change literature (my field) indicating that this is an option. Anybody out there hear of this?

Also: If I stick with the TCD/ECD detector mix, as I think I will, I know I need to think carefully about backflushing issues to prevent O2 and H2O from getting to the ECD. I'm looking for some input about where to turn. I hear great things about Varian, and would like to know if anyone has experience w/ HP, Agilent, or SRI's ECDs. I have researched this a bit and have a hard time finding labs using ECDs that come in these brand instruments. Anyone out there doing such analyses who can comment?

Thanks very much.
Yankee

[Ron]

The main problem with the Valco detector is lack of linear range. It is a very good detector for trace levels, but I would imagine that your methane concentrations would fall into the non-linear range.

Shimadzu has a turn-key greenhouse gas analysis system which is designed to measure N2O, CO2, and methane using a TCD and ECD for the analysis.

[yankee]

Thanks for your reply - but your response confuses me. The Valco detector? Do you mean Varian? Or Valco valve?

I think the Shimadzu instrument must use a FID for CH4.

Regardless, does anyone out there have experience with or knowledge of an instrument that can effectively measure CO2 and N2O from one injection, on a TCD and ECD?

Thanks.

[Ron]

Yankee, the helium discharge detector that Varian is suggesting is probably the one made by Valco. Even though Valco is often thought of as only a valve company they also make detectors.

The standard Shimadzu configuration uses only a TCD and an ECD. Some systems have also included an FID for hydrocarbons, but in greenhouse gas samples often methane is high enough in concentration to be detected by the TCD.

[GasMan]

Yankee,

Perhaps you would let us know the concentrations that you are looking for of these gases, and also the matrix that they are in. The Valco PDID detector will certainly measure N2O. Once we know the concentrations, we can work out the best detector combination. You may want to consider the implications of using and ECD, you will need to get clearance to have the radioactive detector in the lab, and if in the USA, you will need regular wipe tests. This is not needed with other detectors.

Gasman