benzylchloride1
Hazard to Others
Posts: 299
Registered: 16-3-2007
Member Is Offline
Mood: Pushing the envelope of synthetic chemistry in one's basement
|
|
Gas chromatographs
I recently obtained a helium cylinder for my Gow Mac 150 gas chromaograph that has been sitting in my lab for the last year and a half. The instrument
will separate various organic compounds, but the peaks seem to be very broad when they are recorded on the chart recorder. The system uses 4ft long
packed columns. These columns are over 30 years old. Could the columns be defective?
|
|
|
matei
Hazard to Others
Posts: 205
Registered: 16-9-2006
Member Is Offline
Mood: No Mood
|
|
Packed columns have lower resolution than capillary columns, so the peaks should look somewhat broad, but I think you should replace the stationary
phase after it stood in air for 30 years  . Also you should check that the
stationary phase is suitable for the compounds you've tried to separate (e.g Apiezon is good for nonpolar compounds, Carbowax for polar compounds like
alcohols and silicone oil has a general applicability).
|
|
|
Klute
International Hazard
Posts: 1378
Registered: 18-10-2006
Location: France
Member Is Offline
Mood: No Mood
|
|
Most of the modern macro-bore columns can be adapted on "old" packed colum machines, using the same injector and detector, and offering a better
resolution. Check out the prices for the adaptators, it's often worth it when you don't want to purchase a whole new setup.
You coudl try heating your column quite highand purging it with helium to remove adsobed water and all the other residual gak that could ahev
collected, and try usign it again. If you still haev very broad peaks, it surely is unusuable.
You are one lucky bastard! I dream of having GC apparatus at home...
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
-Alice Parr
|
|
|
benzylchloride1
Hazard to Others
Posts: 299
Registered: 16-3-2007
Member Is Offline
Mood: Pushing the envelope of synthetic chemistry in one's basement
|
|
Here is a print out from the chart recorder connected to the instrument. After several minutes the instrument goes all the way to zero and does not
record any more of the sample. The samples are turpentine and nitromethane racing fuels.
Attachment: Gas Chromatograph print out.doc (1.1MB)
This file has been downloaded 23927 times
|
|
|
matei
Hazard to Others
Posts: 205
Registered: 16-9-2006
Member Is Offline
Mood: No Mood
|
|
It looks like the sample just goes through the column, and there is no separation of the components. Turpentine is quite a complex mixture, and I
think it would be hard to separate it even with good packed columns. I guess you could try first some simple mixtures like benzene and cyclohexane in
CH2Cl2 or something.... Also, can you provide more info - like carrier gas flow, temperature program, amount injected, type of stationary phase, type
of detector (it's a TCD isn't it)?
|
|
|
benzylchloride1
Hazard to Others
Posts: 299
Registered: 16-3-2007
Member Is Offline
Mood: Pushing the envelope of synthetic chemistry in one's basement
|
|
This system uses a thermal conductivity detector or a TCD. I was running the helium into the instrument at 60 mL per minute. The instrument was a 150
degrees C. A carbowax packed column was used, from what I have heard, I need to replace the columns.
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
