Hydrocarbon packed column question.

[Shadowsfall]

Hi, and thank y'all for having me. I work for a hydrocarbon logging company in West Texas. We are using a packed column to separate c1 to c5. In our old columns, acetylene had roughly the same elution time as propane. Does anyone here know how that might have been accomplished?

[GasMan]

The fact is that when your GC was purchased, somebody asked for a system to separate C1 to C5, probably no mention of acetylene. The column supplied will separate C1 to C5 but probably not acetylene from propane. No matter what you do by changing flows or temperature, the separation will not happen. You will probably need a multiple column system or move over to capillary or PLOT columns. My limited experience with mud logging systems has also told me that users require a very short analysis time, and you may not be able to accomplish this to get the separation that you require.

I suggest that you contact the supplier of the GC and ask what they recommend or ask a company that specializes in mud logging applications.

Gasman

[chromatographer1]

Acetylene when put onto a column with some polarity will elute later than its carbon number would lead you to expect.

Is there more to your question other than a simple explanation of polarity of the column phase or support?

best wishes,

Rod

[Shadowsfall]

Sorry about the lack of clarification. We are trying to pack our own columns for the first time. In our column, Acetylene is coming out with Methane(c1). We use calcium carbide pumped down a well bore to calculate lag time for samples(as we are typically drilling to 4000'+). Since methane is a predominant background gas, it is difficult for us to see the acetylene peak if it elutes in the same area. Our old columns(also packed) eluted the acetylene where propane(c3) would be. Specifically, I'm asking if anyone knows of a packing technique or material that would slow the elution time of acetylene without changing the elution times of C1 through C5.

[chromatographer1]

Shadowsfall

You want a change in your column packing that moves acetylene back in retention, but does not change the RT of methane through pentane. In other words, keep what you have but change it so it doesn't change anything except acetylene in retention time.

Okay, that sounds like a chase for a wild goose. And I hope you can see that.

But the 'asked for solution' may not be the issue here.

The issue here is you have a packing where methane coelutes with acetylene. I cannot image this EVER happening in real life with ANY column that will elute C1 through C5.

Could you please post a few chromatograms (see under the LC forum for directions) of your results.

Why? Well, I am from Missouri, the SHOW ME state.

A description of the packing and any phase used with it would be very helpful in diagnosing your problem.

Does your original column still work as it is supposed to work? Are you using the same packing and phase to make your new column?

I cannot imagine it could be a packing problem.

I suspect your acetylene is (take your pick) :

1. being consumed and never leaving the column, eluting only a methane contamination.
2. is not acetylene, but is really methane.
3. is being retained SO WELL it is taking a long time to elute from the column, eluting only a methane contamination.

BTW

I came up with a micropacked column to do this C1-C5 analysis in 30 seconds, and my company GAVE away the proprietary details to a customer. The resolution of methane and ethane was only about 80% but the other peaks, including neopentane were all separated.

I still have the original micropacked column which I packed myself and it was run on a HP 5890A GC.

best wishes,

Rod

[Shadowsfall]

Sorry about my slow replies. And yes, I realize what a wild goose chase this could be. But I also know there is a chance that somebody out there knows exactly what I'm referring to. I won't be back around the office to get you some chromatograms until the 5th. I'll post those for you then. Our acetylene is definitely acetylene, we are getting it from calcium carbide. The old columns we still have do still function as stated previously(acetylene eluting as c3). We have removed the packing from one of these that had taken on water. After drying it out, mixing it and repacking it, the column still behaves in the same manner. We are still not sure what phase is used in these columns. The columns we have packed ourselves are diatomaceous earth and squalene.

[chromatographer1]

To have acetylene elute with methane indicates that the separation of C1 and C2 is minimal, and the peak width is as wide as the separation achieved with the diatomaceous earth and Squalene phase column you are using. This of course is slightly more polar than squalane, but not polar enough to affect the separation of methane and acetylene.

You are probably using white earth, not pink, and are loading the phase at levels less than 35%, and or are using a rather short column.

The packing material you have not described is probably off-white in color, and spherical in particle shape, not irregular in shape as is the earth. It is silica based and is synthetic. Unfortunately, the original manufacturer no longer produces it. Restek has attempted to sell a similar product but performance is not identical to the historical.

Good luck,

Rod

[AICMM]

Shadowsfall,

Have you looked at Res-SilC packing from Restek? This is what I used on the mud-logging instrument I built for a customer. It elutes the acetylene near the propane but still gives good resolution between the C1 and C2.

Best regards,

AICMM