Analyzing Cooking Gas/Liquefied Petroleum Gas Using GC-MS

[nuruddin]

I am currently trying to analyze some samples of gas suspected to be LPG or Liquefied Petroleum Gas. From what I've read so far, LPG consists mainly of propane (C3H8) and butane (C4H10). When I tried to analyze the gas sample using the GC-MS on my lab, I obtained a broad peak which I suspect is the propane and butane peaks merged together. I have been trying to find ways to improve the separation of my samples but have met with little success so far. I am using Perkin-Elmer Clarus 500 GC-MS with TurboMass ver 5.4.2.1617 software, and using the headspace injection method. Please advise. Any feedback on how to adjust the parameters (carrier gas flow, ramp-up temperature, etc) using the TurboMass software is also appreciated. I suspect that I might not have set the carrier gas flow correctly.. but I cant be sure. (PE's software is more complicated than the software I normally use).

[Don_Hilton]

Using the common columns, such as DB-1 or DB-5 can give some separation of propane and butanes if you can keep the columns cool enough - (oven temperatures about 35 degrees C or so.

So, I would suggest that you give the conditions you tried - column, carrier, column flow rate, injection conditions, etc. and perhaps we can help from there.

[nuruddin]

Here are the conditions I used for my GC-MS run attempt:

Column: DB-5
Oven Temperature: Initial - 35 deg C (hold 10 minutes), Ramp-up: 5 deg C/minute, Final - 150 deg C (hold 10 minutes)
Carrier gas: Helium, 0.5 mL/min split flow
Injection conditions: Headspace, Injector Port Temp: 200 deg C
Sample amount injected: 1 mL
GC to MS Inlet Line Temperature: 200 deg C
MS Source Temperature: 200 deg C

Latest attempt using these conditions result in the same broad peak I've encountered before.

[bhuvfe]

Here are the conditions I used for my GC-MS run attempt:

Column: DB-5
Oven Temperature: Initial - 35 deg C (hold 10 minutes), Ramp-up: 5 deg C/minute, Final - 150 deg C (hold 10 minutes)
Carrier gas: Helium, 0.5 mL/min split flow
Injection conditions: Headspace, Injector Port Temp: 200 deg C
Sample amount injected: 1 mL
GC to MS Inlet Line Temperature: 200 deg C
MS Source Temperature: 200 deg C

Latest attempt using these conditions result in the same broad peak I've encountered before.

1-1.2 ml is generally the optimum flow.

Which column size are you using?

And at which split ratio?

[Peter Apps]

You are volume overloading the column. Reduce your injection volume and/or increase your split ratio by a factor of a least 10.

Peter