HP/Agilent 6890N : analyzing ppm levels of organics in CO2

[www_ups]

Hi,
I am a grad student working on how to convert CO2 to fuels. Unfortunately, the method of my choice can only produce ppm levels of organics (CO, CH4, CH3OH, HCOOH...) at the outlet of my reactor. So, I am faced with the question of analyzing low concentrations of organics on a HP 6890N with a GS-GASPRO Agilent (capillary?) column with FID & TCD detectors. Agilent customer service said that while separation of various components should not be an issue, the detector might not detect low concs. of organics.

1.Could any one suggest means to increase the sensitivity of the detector ?
2. Another is the issue of quantification: my GC has an auto sampler, though I am fairly aware of how to prepare gas standards (volumetric dilution), I think I need a pressure of atleast 2 bar for the sample to pass through my system to teh GC. Could anyone suggest ways to prepare pressurized standards (Supelco's have to be diluted to the ppm levels) ?
3. The final question is about the use of autosamplers in general, could anyone kindly suggest good introductory books on how to use auto samplers in gas chromatography ?

thanks,
pradeep

[chromatographer1]

Your TCD is not the detector of choice for low level detection.

Your FID may not see formic acid formaldehyde methanol and other possible partially oxidized reaction products at low levels because they may not elute from the column or because of low detector response.

In addition, using a capillary column which has limits to the amount of sample you can inject onto it, is also a problem.

I would recommend a packed column, depending upon which analytes are necessary and which are optional. For example, if formic acid was a critical issue, I would only use a FFAP or SP-1000 coated porous polymer or carbopack support.

If separation of ppm levels of analytes from a large amount of CO2 then the porous polymer is a good choice. If CO is critical then you are limited to molecular sieve (zeolite or carbon based) or to a very long packed methyl silicone coated Chrom P support column.

The best detector for your analysis is a helium discharge detector like one from GOW-MAC or Valco.

Valco's detector can be a direct replacement for a Agilent FID.

Good luck in your research.

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

800-359-3041 tech service
techservice@sial.com

[www_ups]

Hi Mr. George,
Thanks for your reply. I 'm a student @ Penn State, University Park PA currently at the University of Nottingham. So the equipment I am working with is not owned by my advisor. Hence, getting a new detector might take some time. Meanwhile however, I see some peaks in the FID when I run my expt. The next part is to identify and quantify them. We have an autosampler for injecting samples. I had earlier worked with manual injection systems and am familiar with the basics of how to dilute standards. Is there any chance that Supelco supplies ~1% each of permanent gases (O2, H2, CH4,CO, N2) in He ? I had a 1% standard in N2 but would rather have a standard in He (my carrier gas) than N2.

Also, could you tell me if I could get standards of CH3OH, HCHO in CO2/He or how to make them? (My idea is to inject a given amt/time into a flowing CO2 stream..)

Thanks,
Pradeep

[chromatographer1]

Permeation tubes are the best solution to your need to spike a flowing stream of CO2 with contaminants.

You can add different amounts depending upon the flow rate through the tube.

Call Supelco Technical Support and they should direct you to the proper products. 800-359-3041

or use email:

techservice@sial.com