Propane/Butane GC analysis optimization help

[Evmm]

Hi all.

Having some "problems" running this analysis at the moment, i'll leave the equipment that I'm using.

Agilent 7890B, Packed 20% Sebaconitrile Chromosorb Column, FID, injection through a gas valve, trying to apply to EN27914.

The software (Chemstation) brought a standard factory method for quantification of these 2 components that I'm trying to run, using 100ºC inlet temp, 30ºC Oven temp, 150ºC on FID with H/air 30/300 and HE as carrier @ 32ml/min.
The result using these conditions is a pretty good chromatogram but the first 2 components (Ethane and Ethylene) come off as an overlapped peak (split peaks), and I'm trying to optimize it to have a better result, since I need to calibrate and validate the method itself for all the components present on the standard I'm using.
Tried playing around with temperatures, ramp up on oven and all that, but the result itself doesn't vary much.
The norm that I'm following says that these 2 compounds usualy come out as a single peak on most columns, but still I am searching for a best "combo" to have the best final result as possible.

Anyone got any suggestions?

[GasMan]

I do not think that you will have much success. In the refinery gas analyzer that Agilent offers that uses a sebaconitrile column, the separation of ethane and ethylene is carried out on a Porpak Q column.

Gasman

[Evmm]

Thanks for the reply Gasman.

I searched online for some examples and found out a result using the type that you mentioned..
So, for the best result possible, the only possible way would be to get that type of column right?

[GasMan]

I am not familiar with the EN27914, is this a single column method?

The analyzer that I mentioned in my earlier message is actually using three valves, a 10 port valve and two 6 port valves. The 10 port valve injects the sample into two sebaconitrile columns in series (a long column and a short column). By selecting the correct "OFF" time for the 10 port valve. C6+ compounds can be backflushed to the detector. The two six port valves are configured as column isolation valves, one has the Porapak Q column and is used for the separation of CO2 and the C2's and the second valve has a Molecular Sieve column for the separation of O2,N2, CH4 and CO.

If you need separation of all of these compounds you will find that the only way is multiple columns.

Gasman

[Evmm]

Hi Gas,

Yes, it uses a single column method to quantify Propane and Butane in Liquified Petroleum Gases and their commercial mixtures, from C2 to C5, saturated or not.

The GC I have here itself uses one valve system, the ON/OFF times are already placed with the method, I haven't tried changing them since I don't think it will improve results, but hey, doesn't hurt to try though.
Also, I only have that single sebaconitrile column, sadly..

Was trying to use a calibration standart that was bought and those 2 compounds come very close to each other, which is doing some trouble to the calibration and the software itself keeps popping up the overlapped peaks message... think that this result will have to do.

[muGC]

Sounds like you should be implementing ASTM D2163 instead. The columns recommended for this ASTM method are DB-1 equivalent 100m x 0.25 x 0.5 or AL2O3 PLOT equivalent 50m x 0.53mm x 15um.

[Evmm]

Thought of that muGC, but the conditions used for those columns I can't use here, since my max temp on the column is 75ºC.

[muGC]

No I am suggesting that you are using the wrong column and method.

[Evmm]

The column itself maybe is a problem on these 2 compounds, but the method itself isn't. The EN one is directed to Propane or Butane quantification specificaly, while the ASTM (or ISO 7941) is directed to hydrocarbons in general. Take in mind that all of these are LPG related.

[muGC]

If the EN method is designed for Propane and Butane but you need to have a method that works for all your hydrocarbons, then ASTM D2163 seems to be the more appropriate method. Right?