FAST GC - MICROBORE COLUMNS

Chromatography Forum: GC Archives: FAST GC - MICROBORE COLUMNS
Top of pagePrevious messageNext messageBottom of pageLink to this message  By P Ph GARRY on Wednesday, July 19, 2000 - 10:14 am:

We are working in essential oils analysis, with GC. We often use DB or Carbowax columns (60 m or 30 m, 0.22 dia). We want to do faster chromatography (15 min instead of 70 min). So we are interested by microbore columns (100 microns dia, 20 m) but many people said to us that we need an electronic carrier gas pressure control. I agree that it seems to be true, because at this diameter you need higher and higher pressure to have good chromatographical answer but the investment for this instrument is quiet important. So I would like to know if somebody have experience of this type of column.

Pierre Philippe GARRY


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Paul Peterman on Thursday, July 20, 2000 - 02:30 pm:

We have been using a 50 m x 0.20 mm i.d. x 0.11 um (Ultra-1 or 2, HP now Agilent Tech) with helium gas up to 350 kPa (50 psi) with a manually-regulated pressure valve on our HP 5890A GC, which was made before electronic gas pressure control. If you use a septum in the GC inlet, you are more likely to have shifting retention times than you would by using electronic pressure control. However, with the high pressure capacity of the Merlin Microseal (septumless system), retention times have been quite reproducible using manually regulated head pressure control and inlets up to 285 deg. C! An alternative septum-less system that might work is the Jade Valve.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By schnorbus on Monday, July 24, 2000 - 03:07 am:

Your problem, with fast GC-Analysis, can been solved immediately. Have you ever tried EZ-Flash ? (or heard of it). Your GC-measurement of 70 minutes can be done in let's say 7 min (or less), on a 10 meter column (of your choice) with better resolution than you would get on your regular GC-column (60m), if you are looking for compounds lets say between Kovat's Indices 800 - 34000. If you would like to hear more, feel free to send me an e-mail. : Harald.Schnorbus.HS@bayer-ag.de


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Jason Ellis on Monday, July 24, 2000 - 08:54 am:

While electronic pressure control would be nice to have, I wouldn't consider it essential to your application. EPC inlets allow high operating pressures as well as the ability to maintain constant flow throughout your temperature program. The abiliy to ramp headpressure during a temperature program can improve analysis time and efficiency, however microbore high-speed GC was performed long before EPC inlets were available, and we have performed many applications here using older 5890 GCs with manual pressure regulators.

At very high headpressures, I agree that the Merlin Microseal (or similar) septumless system would be a good choice.

EZ-Flash works very well for reducing analysis times of relatively simple mixtures, however it tends to lack the resolution required for complex mixtures partially due to its use of large-diameter columns. For high-resolution methods you just can't beat the resolving capabilities of small-diameter columns.

If you are interested in seeing some chromatograms using microbore columns on non-EPC systems, please e-mail me directly.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Paul Adams on Monday, July 24, 2000 - 01:51 pm:

EPC is nice but not essential for high-speed analysis. A high speed sample injector does however seem to be an important component (not too pretty to hand inject into an inlet at 100 psig), regardless of the merlin or traditional septa inlet.

Switch to hydrogen carrier, if you are not using it already.

When translating a method from conventional GC to high-speed GC I've found the free Agilent method translation software is a good place to start. It's at http://www.chem.agilent.com/cag/servsup/usersoft/main.html#mxlator I've had great luck translating Carbowax methods and having them come out with identical separations.

I agree with Jason on EZ-Flash. It is not a good answer for complex mixtures at all.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By schnorbus on Tuesday, July 25, 2000 - 11:50 pm:

It's nice to see that you agree with each other, as far as EZ-Flash is concerned. On a regular GC-Column 30 m x 0.2 mm separation of two compounds with (2) Kovat's Indice difference is expected. With the EZ-Flash system, the same column 10 m x 0.2 mm will separate compounds with (5) Indices difference. If that separation is not sufficient then just choose a column of higher or lower polarity. Complex mixtures are here no problem. So you see, it is usually not the system that is at fault, it is partly a matter of the quality of the person setting up the analysis.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By paul adams on Thursday, July 27, 2000 - 06:36 am:

The quality of the person? hmmm.....I don't think we've ever met, so might be hard for you to judge.

My EZ-Flash judgements are based upon separations I've seen with my own 2 eyes (or have not seen as is the case here). EZ-Flash personnel brought a system in and tried to duplicate some analyses I provided them of complex mixtures. They were unable to do so after several attempts. These were analyses that had 100 or more components and typical run times of 45 minutes. I was able to exactly duplicate much of these with mini-bore columns and run-times less than 10 minutes.

Unless significant improvements were made since I last saw the system, the EZ-Flash system remains a novelty. I recommend saving your money and putting it into a nice new GC.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By schnorbus on Friday, July 28, 2000 - 02:21 am:

Let me give you a second opinion on EZ-Flash.
For every job one needs the right tools. Now you will agree with me that it would be relatively orthodox to use a Plot-column to measure compounds in the range of Is 2000. on the other hand a CMS column (HP1 OV1 or similar) is not as effective when measuring compounds with Is<400 . Its the same with EZ-Flash , the right tool for the right job.

If your samples contain 100 or more peaks, you may need a special column and a special GC-method designed especially for your problem. EZ-Flash may not be the right system for you (even though I doubt it). Nevertheless, other labs have other problems and we find when doing reaction monitoring, EZ-Flash is the ideal system to use. The number of compounds in a sample is irrelevant. Relevant is, to find out in the shortest possible time, if the reaction being monitored can be stopped or not and to know with in minutes what other components may have formed. You may not have all the facts. Don't knock a system if you don't know how to use it.


Top of pagePrevious messageNext messageBottom of pageLink to this message  By Brian Kochanowski on Tuesday, August 1, 2000 - 07:55 am:

Iím going to jump into this exchange here because I have experience on using both types of systems (small bore < 0.1mm ID and EZ flash). Both methods have their limitations, and whether that limitation is considered a small or large disadvantage is related to the basic use of the instrumentation-"Does it solve my problem?" If not, then it becomes, as Paul said, a novelty. It sounds like the system works well for the samples Harald has. I had great success in reducing a 20 min. separation of about 18 components to 90 sec. using the EZ Flash system. When using the EZ flash for some pyrolysis work, I noticed the same problem that Paul did, and that is in analyses of complex mixtures. Pyrolysis of polyethylene gives a distribution of triplets related to the carbon chain out to at least C30. Because of the shorter columns used in the EZ Flash, the total resolution is lacking for this separation. I might have had better success with a different column in regards to phase type and thickness, but it wasnít necessary so I didnít try. There is the biggest advantage (in my opinion) of the EZ Flash, you can request any currently manufactured column be put into the EZ Flash column configuration.
With the small bore columns, you are limited to what the column manufacturers are offering. I use a Rtx-volatiles column for a number of analyses, and I would like a to use a 0.1mm ID with hydrogen carrier gas to get the fastest separation possible. Iím out of luck, the smallest I can get is a 30m 0.25 mm ID. Anyone who uses PLOT columns regularly has the same problem, the smallest youíll get there is 0.32 mm ID. No problem with DB-5 separations though. I have used the small bore columns and the HP method translator software for the previously mentioned pyrolysis method to easily reduce the analysis time from 60 min to 10 min. And I will also say that this is the easiest and cheapest method to implement if you already have a high pressure inlet on your GC. As always, you should be developing or purchasing the best solution to your problem, not the most fascinating technology (even though as an analytical chemist I would like to have it anyway).


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