Fast GC

[jtreacy]

Excuse me if this is a naive question but do you need special apparatus to run fast GC columns or could I use the Agilebt 6890 that I already have?

regards

John

[jakkie]

Your normal Agilent 6890 will do the job just fine, but I would recommend that you check whether you have a 150 PSI EPC unit. The "standard" 100 PSI unit sometimes does not give enough pressure to give the optimum high flows needed for fast GC.

[jtreacy]

Thanks for that. I will look into it in more detail in the new year.

John

[gcguy]

First job would be to check on your gas supply.
We had to get ours revamped as the regulators etc would not give us high enough pressures. If you are planning to use generators check to make sure they will give you enough to allow for the high pressure and (usually) high split flow.

We have had some fantastic results using narrow bore columns and as we have not modified our 6890s there have been no capital costs.
I am sure that when you start developing methods you wonder why you didn't look at it before.

Good luck

GCguy

[GasMan]

jtreacy,

If part of your fast GC method involves fast oven temperature ramps, then your standard 6890 may not be good enough. This depends on what part of the world you are in. If you are in the part of the world that uses 220Volt as the standard voltage supply, then you will be OK for fast oven ramps. If you are in the 110 volt part of the world, you would need modifications to the oven heater and you would also need to have a 240 Volt supply available in your lab.

Gasman

[jtreacy]

Thanks for that guys - you have saved me hours of reading by sharing your experiences. Our lab is in the UK has a 240V supply.I don't know how the gas supply will cope yet - it is a cylinder based system - we tried generators but they always seemed to fail without warning when the most important jobs were on and we ditched them. I'm really looking forward to trying Fast GC as I've been astounded by what Fast HPLC can do as I'm pretty impatient (why don't they call it Fast HPLC? obviously the GC fraternity are more pragmatic!).

Thanks again

John

[lmb]

Dear jtreacy,

The answer to your question very much depends on the column and on the carrier gas in your applications.

Fast GC usually means different things for different people. For some, fast GC is GC with 0.1 mm and smaller bore columns. The reason for that is that these columns of any length produce a lot of peak per time. However, the requirements to a GC instrument very much depend on the column length.

Examples:
1) 3m-0.1mm column with hydrogen as a carrier gas requires a modest pressure of under 20 psi (120 kPa), but the heating rate should be close to 300 ºC/min. To my knowledge, commercial GC instruments with air ovens do not provide this rate.
2) As another extreme, consider a 40m-0.1mm column with helium. It requires a very modest heating rate of under 10ºC/min, but pressure should be well above 100 psi (690 kPa).

Most likely, the conditions of your analysis are somewhere in between and your 6890 GC can be OK. Hydrogen is up to 70% faster than helium. It is also less demanding on pressure, but more demanding on heating rate than helium. For more specific advice, you need to provide more specific data.

[jtreacy]

IMB thanks for the information.

I'm sorry I couldn't suply more information. At this stage we are just looking at whether it would be worthwhile to pursue Fast GC in the future - from what I've read and from people's helpful comments here it looks like it could be a viable option even if it is only 'Faster' rather than true Fast GC.

John

[lmb]

Hi jtreacy,

Go for it. You might be surprised how easy it is. To save your method development time, you might try GC Capillary Column Method Translation Software available from Agilent, www.chem.agilent.com/cag/main.html, at no charge. You can also use that software for all sorts of "What If?" tests.

In previous posting, I forgot to add that columns with larger diameters are less demanding on both pressure and heating rate.

lmb