New GC configuration for biogas analysis

[peerm.abdul]

Greeting guys,

I'm a postgraduate student from Malaysia. My supervisor is planning to get a new GC set for our lab. Below are the specifications:

Shimadzu Gas Chromatograph Model GC-2014AT
complete with:
- 2 x DINJ-2014 (dual packed injector)
- 2 x TCD-2014 (Thermal Conductivity Detector)

Technical Specifications
Column Oven
- Temperature range: Room temperature +4 oC - 400 oC
- Programmed rate setting range: -250 to 250 oC/min
Injector
- Independently temperature controlled injector units with AFC

Detectors:
Thermal Conductivity Detector (TCD)
- Temperature range: up to 400oC
- Dynamic range: 10^5.
Display:
- 240 x 320-dot graphics display (30 characters x 16 lines)
P/N: 221-70027-34

Gas Sampling Valve
Gas sampler with 6 port valve with adapter, MGS-4
P/N: 221-42574-02; 221-42868-91

Stainless Steel Packed column
Shincarbon-ST 50/80 (6m x 3mm ID)


For your information, our lab is interested to quantify biogas composition in % (v/v)
Based on our previous results the gas composition: hydrogen (25-45%), nitrogen (about 0-20%), oxygen (0-20%), methane(in the absence of hydrogen gas, about 35-55%), carbon dioxide (35%-45%).


I would like to have your comments/opinion whether this GC configuration is sufficient for our analysis? Thanks in advance.

[rb6banjo]

Looks like that should do it. At those concentrations, the TCD should be good for those analytes. Are there other, maybe more trace-concentration components that you might wish to detect as the project develops? TCD is not the most sensitive of GC detectors. If you're buying a new GC, it's easier to get a flame detector already installed than it is to install one later.

[peerm.abdul]

Yes we are planning to get a new units only for biogas analysis. Im not sure what is the minimal LOD for TCD for all these gases.

Previously in our lab we used SRI 8610 C (equiped silica and molecular sieves column, Detectors: TCD and HID), works well for our applications. I like SRI system for easy handling. But we could not find a suitable vendor to service the units locally. We had to ship it back to USA for maintenance.


We are thinking about H2S (hydrogen sulphide gas) but at trace level, any suggestion for H2S detector would be helpful.

Im just curious whether this column able to separate simple volatile organic acids (ethanoic, propanoic and butanoic acid) and volatile alchohols (ethanol).

[rb6banjo]

I'm not sure about that. Restek doesn't call those analytes out in their literature on this column.

http://www.restek.com/pdfs/PCTS1472-UNV.pdf

Those are all reasonably nonpolar analytes. Carboxylic acids are a different animal altogether. If you don't derivatize them, they are very difficult to chromatograph. A wax phase is the only thing I've ever used successfully.

[AICMM]

peerm.abdul,

The forum is littered with this problem. So the same warnings apply here that apply elsewhere in the forum. A single TCD will be hard pressed to do both hydrogen and the others with any kind of efficiency. The issue being that using argon carrier for hydrogen analysis will yield poor sensitivity to other components and using helium carrier for other components will yield anomalous hydrogen peaks. Which is probably why your SRI had the HID installed. So, either two channel two TCD or one channel HID to get where you want to be. (Standard disclaimers about HID's applies here.)

Willing to discuss further if you are so inclined.

BEst regards,

AICMM