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identification of heavy sulphur compounds in LPG with GC-MS
Posted: Mon Nov 29, 2004 10:13 pm
by Cobre
I have to identify sulphur compounds ( C3+, disulfides, trisulfides and...) in C2-C5 LPG( appr 60%olefins) with GC-MS. Has anyone experience on doing this, or can someone help me to find the best way of sample introduction( inlet temperatures, GSV, LSV, COC.....) and column ?
Have been using a CP-SIL 8 ( 25*0.53*5) until now
Thanks in advance!
Injecting LPG
Posted: Tue Nov 30, 2004 7:28 pm
by Les
The problem with LPG is discrimination. The light ends in gas state and the heavy in liquid state. Many use a water bomb pressurized by nitrogen at @ 500PSI. I too would use that system, however, I don't want water to accidentally enter my GC. So now I just press 600 PSI nitrogen pressure on top of the LPG in a 300 cc steel peanut bomb. The pressure liquifies the gases and the sudden rush of nitrogen mixes the sample. The sample is injected with a 0.2ul liquid sampling valve from VICI. The system works pretty good. The valves require changing on a regular basis (about 6 months) due to traces of water and dirt. Yes I do have filters (actually 2, 15 u and 0.2 u) but still gets to the valves. I send them back to VICI and they re-condition for a fee of course.
The sulfur issue is a different beast. Clean sample lines and calibration standards are not cheap. Deactivating everything in the path to the detector is always a challenge. Getting mercaptan in and out without converting to sulfide will be a challenge.
I'd like to know how things turn out. Drop a note once in awhile to let me know how you're progressing.
Posted: Tue Nov 30, 2004 8:49 pm
by Cobre
thanks Les. It's good to hear the LSV works fine...had some doubts about that. I also pressurize my sample bombs with nitrogen up to appr. 500PSI when I use my VICI micro-flo syringe (for manual injection of liquid LPG), so I'am familiar with that.
It will take some time but I will let you know if we're making some progress..