Questions about LPG analysis w/ PLOT columns & H2 carrier

Discussions about GC and other "gas phase" separation techniques.

4 posts Page 1 of 1
Hey guys,

I run ASTM D2163 with an alumina PLOT column for C1- C6 hydrocarbon analysis via an FID. The scope of the analysis is for the calculation of main components and trace C3 and C4 olefins in propane, isobutane, and n-butane blends. Currently I use Helium as my carrier and it's great but I would like to transition to H2 carrier.

A big headache which requires method development and can be variable from column to column even from the same manufacturer and column type is the separation and co-elution of neopentane from the C4 unsaturated hydrocarbons. It will usually co-elute with isobutylene. Usually flow and temperature can be modified to circumvent this.

I have nicknamed this the "Neopentane dilemma". Anyways, has anyone had any success with using Hydrogen carrier for this or a similar analysis? Most references utilizing a PLOT column for the analysis of hydrocarbons uses helium carrier.

A partner with our GC manufacturer has said that PLOT column lifetimes are decreased when they have attempted to develop methods using hydrogen carrier. Also, neopentane coelution is more difficult to remedy.

Feedback would be much appreciated.
I haven't used the PLOT columns but if you are getting away from Helium because of cost, have the tried it with Nitrogen carrier?

There are several papers out recently of actually using Nitrogen carrier with small bore capillary columns that give favorable results compared to Helium. Shimadzu has even worked with using it with GC/MS though I have not been able to duplicate that work yet with our Agilent.
The past is there to guide us into the future, not to dwell in.
I have not.

My only fear with nitrogen is having to settle on longer analysis times. This may be something I have to accept but the methodologies are employed for QC functions where increased analysis times would not be preferred.

I have not tried the different carriers, however, this is something I will most likely get around to myself. I can give feedback in a few months once I get around to it. I just wanted to put this out there to see if anyone has achieved this very narrow set of criteria.

I do however have some experience having to do method developments for my "Neopentane dilemma". Thanks for the Nitrogen suggestion. I am anticipating the possibility that this is what I may have to do. Slower analysis times but whatever.

I have a theory about analyzing trace unsaturated hydrocarbons, that hydrogen carrier will actually reduce the analytes at concentrations < 10 ppm. This seems to be the case when comparing results from our older setups which uses a packed column and hydrogen carrier. This may be specific to packed columns though (i.e. active sites developed on the SS tubing). However, I'm not overly certain on this reasoning.
AeroPH,

My experience switching between He and H2 has been to set the H2 flow to the same linear velocity as the He flow has. This seems to be the most efficient place to start the method development. You do not gain any time advantage but you should be able to maintain hard earned resolution.

REgarding loss of low level olefins, unless you are taking the system to very high temperatures, I would be suspicious of loss due to hydrogen. I have converted several LPG's to hydrogen but not looking down to 10's of ppm but rather low percent so I may not have seen losses.

Best regards,

AICMM
4 posts Page 1 of 1

Who is online

In total there is 1 user online :: 0 registered, 0 hidden and 1 guest (based on users active over the past 5 minutes)
Most users ever online was 1117 on Mon Jan 31, 2022 2:50 pm

Users browsing this forum: No registered users and 1 guest

Latest Blog Posts from Separation Science

Separation Science offers free learning from the experts covering methods, applications, webinars, eSeminars, videos, tutorials for users of liquid chromatography, gas chromatography, mass spectrometry, sample preparation and related analytical techniques.

Subscribe to our eNewsletter with daily, weekly or monthly updates: Food & Beverage, Environmental, (Bio)Pharmaceutical, Bioclinical, Liquid Chromatography, Gas Chromatography and Mass Spectrometry.

Liquid Chromatography

Gas Chromatography

Mass Spectrometry