Chromatography Forum

The setup
GC: Optichrom Advance
Service: EP streams analyzing Methane, Carbon Dioxide, Ethane, Propane, C4+
Detector: 30KΩ TCD
Carrier: Helium
Sample valve and column valve are both 6 port Model 11
Reference flow 22 CM3/M
Carrier flow ( Det vent) 40 CM3/M
Reverse Column Step
Columns:
1 5ft 20% 0V-101 – 80/100 CHROM P
2A 1 ft HAYESEP Q -80/100
2B 2ft HAYESEP P – 80/100
2C 14 ft CHROMOSORB 750 – 80/100
3 1 ft 20% 0V-101 – 80/100 CHROM P
With CV1 on flow is Carrier >1 > ITC > 2 >3 > DET > Det Vent
With CV1 off flow is Carrier > 2>ITC<1>3 > DET>DET vent

My issue with this analyzer is both the CO2 and the Methane Peaks are reading much higher than they should be on one of the streams. The CO2 is reading anywhere from 0.01% off to 0.04% off. The Methane is reading about 2.5% or 2.75% off.
I tried checking that stream on the other two streams on this analyzer (just used a jumper on the tubing over to the other stream) and the results were pretty consistent on all streams. This leads me to think that it is either a sample issue or a timing issue on the gates and reverse column step. I replaced the vaporizing regulator at the sample point which is a long distance away from the analyzer. I am not sure if the regulator is working properly as there is no documentation on them that I have been able to find, they were rebuilt in 09 so they were not new in the warehouse. Any documentation that may have been with them new is long gone. Go regulator PN H2-108358 which I have been told is a custom part for Siemens?
I can upload screen captures of the grams if needed.

thoughts on where I should go from here?
Thanks

From what I understand your analysis is good except for one stream which appears to be in error.

It appears your sample is liquid and under high pressure.

You suspect your vaporizing regulator is not producing a representative sample from the stream, since your methane and CO2 are running high values.

It does sound like your regulator is not vaporizing properly giving you samples higher in the more volatile gases.

Oh, the old Model 11 valve ! They just keep going and going and going.....

Rod

ok that will give me some more stuff to check

I checked the tubing run ( between 450 and 500 feet) and there did not appear to be any leaks had 17psi on the regulator outlet and 16psi on the inlet for the analyzer itself

and yes the 11s seem to be fairly good as long as they are put together well in a clean place

thanks for the tip

after I did some checking on the regulator just for kicks I ran the cal gas on the stream we are having issues with and the methane was about 2.5% high, the CO2 was actually low by about .1

tomorrow I am going to pull samples on the other 2 streams to compare them, they may be reading off as well I am not sure