Chromatography Forum

hello folks.

since the first generation 5890A GC's are not equipped with EPC, you cannot set a constant flow as dictated by modern capillary column applications. What are the workarounds for this?

http://www.restek.com/images/cgram/gc_ff00649.pdf

This is for example one of the apps in mind. Would you consider installing it on such an instrument?

hello folks.

since the first generation 5890A GC's are not equipped with EPC, you cannot set a constant flow as dictated by modern capillary column applications. What are the workarounds for this?

http://www.restek.com/images/cgram/gc_ff00649.pdf

This is for example one of the apps in mind. Would you consider installing it on such an instrument?

No EPC module doesn't imply lack of constant flow regulator.

Constant flow regulators were invented long before EPC.

Check carefully specification of your 5890 GC, especially inlet section.

I don't think the 5890A has a constant flow option. does it?

You're right. I believe the 5890A doesn't have a constant flow option unless you have a 5890 Series II mother board installed with an EPC injector board. If you set your flow of 1.2 ml/min at the low temp, your compounds of interest should seperate pretty well until you reach the higher temps (the GC is doing constant pressure with the temp increases). If you have compounds coeluting at the higher temps, you can adjust your column temp ramp to make them serperate as you'd like them.

I am running a series II Plus with EPC, in my method parameters I can choose a flow rate, the comp. then adjusts the pressure as temperature increases.

I also have a 5890 series II with no EPC, there is no option for setting flow rates in the method parameters. I check the flows with a bubble meter off the split vent, purge vent, and FID chimney when the oven is at an average temp. I assume the flow changes during the temp ramp. When I run my FAME reference mix from Nu Chek prep, i just overlay it over my sample to ID peaks. I also use an internal standard.

I am running biodiesel analysis, not as critical as testing food...

The previous lab manager bought an EPC module/board and the flow control valve but never installed it...I might try to install it one of these days...

The advantage of programmed pressure to deliver constant flow as temperature increases is that it gets the analysis done faster - although we spend a lot of time worrying about optimum flow rates the separation that you see on the chromatogram is actually remarkably robust to departures from the optimum - and because gas is compressible the flow rate actually changes continuously along the column so only one tiny bit of it is ever runing at optimum flow.

If you set your flow to the optimum with the oven at the start temperature of the programme the later peaks will take longer to come out. If you set the flow to the optimum at the maximum programme temperature the analysis time will be almost the same as with constant flow but the early peaks will be closer together - which in the separation that you show would present no problem at all.

Peter

hello folks.

since the first generation 5890A GC's are not equipped with EPC, you cannot set a constant flow as dictated by modern capillary column applications. What are the workarounds for this?

http://www.restek.com/images/cgram/gc_ff00649.pdf

This is for example one of the apps in mind. Would you consider installing it on such an instrument?

If GC hardware does not allow upgrade - there is no workaround. Same as computer from 1980 will not work under "Windows 8".

Try to look for older literature sources if similar application exists for nonEPC instruments. It might require some kind of compromise - some peaks not separated, limited range of analytes.

The advantage of programmed pressure to deliver constant flow as temperature increases is that it gets the analysis done faster - although we spend a lot of time worrying about optimum flow rates the separation that you see on the chromatogram is actually remarkably robust to departures from the optimum - and because gas is compressible the flow rate actually changes continuously along the column so only one tiny bit of it is ever runing at optimum flow.

If you set your flow to the optimum with the oven at the start temperature of the programme the later peaks will take longer to come out. If you set the flow to the optimum at the maximum programme temperature the analysis time will be almost the same as with constant flow but the early peaks will be closer together - which in the separation that you show would present no problem at all.

Peter

Thanks for the advise. If anyone is interested I can post feedback of my results when I set this up.

The advantage of programmed pressure to deliver constant flow as temperature increases is that it gets the analysis done faster - although we spend a lot of time worrying about optimum flow rates the separation that you see on the chromatogram is actually remarkably robust to departures from the optimum - and because gas is compressible the flow rate actually changes continuously along the column so only one tiny bit of it is ever runing at optimum flow.

If you set your flow to the optimum with the oven at the start temperature of the programme the later peaks will take longer to come out. If you set the flow to the optimum at the maximum programme temperature the analysis time will be almost the same as with constant flow but the early peaks will be closer together - which in the separation that you show would present no problem at all.

Peter

Thanks for the advise. If anyone is interested I can post feedback of my results when I set this up.

No problem, I got into GC long before there was such a thing as constant flow and EPC. Please let us know how it goes.

Peter

I am interested in seeing it.

Thanks for the advise. If anyone is interested I can post feedback of my results when I set this up.

I am interested in seeing it.

Thanks for the advise. If anyone is interested I can post feedback of my results when I set this up.

okay then. I will post it in November. If you like I can email you with details when it's done.

My separation with constant pressure with the 5890A and helium. Add 5 minutes to the times you see on the chromatogram.



Restek's separation with constant flow and Hydrogen.



Turned out to be a little tricky to set it up. If you wanted to have 1.2ml/min at 240 degrees with this column you'd have to have 370 kpa pressure which is not doable with the non-EPC 5890s. The best you could do with the 5890 was around 0.85 ml/min at 100 degrees in terms of flow. Hope this helps anybody who wants to try it. The column is a CP-sil88 type column.

Apparently the separation that was achieved is very good. Maybe even better than Restek's separation.