Novice Question about GC configuration

[lgchrom]

What is a Dual-FID exactly for? Why does one two detectors simultaneously?

Could it be also be to have two different columns for two different applications on one system?

[Don_Hilton]

There are a number of posibilities. Some instruments ahve two inlets and two detectors and with a pair of autosamplers, can run samples in parallel - incrasing sample throughput without going purchcasing two full instruments. Another possibility is to split from one inlet to both detectors, using two different stationary phases. This allows for confirmation of compund ID with retention indicies on two different stationary phases - or one can inject samples on separate inlets into the two different columns for the same purpose.

[lgchrom]

Thanks for the reply. Is it possible to have 2 different columns installed (one capillary and one packed column) and have 2 different applications on the same instrument. Or is having one column idle when the other one is running, harmful at those elevated temperatures?

[LCbob]

Thanks for the reply. Is it possible to have 2 different columns installed (one capillary and one packed column) and have 2 different applications on the same instrument. Or is having one column idle when the other one is running, harmful at those elevated temperatures?

No problem with this as long as the other column has carrier flow. Just be aware of max column temps.

[Spuzzin]

Thanks for the reply. Is it possible to have 2 different columns installed (one capillary and one packed column) and have 2 different applications on the same instrument. Or is having one column idle when the other one is running, harmful at those elevated temperatures?

The main issue with trying to run two applications (assuming two different columns) is that they will have to share the same oven profile which will make it impossible to optimise separations on both. A compromise wil have to be found somewhere. But this is GC, compromise is the name of the game.

Rich

[lgchrom]

Thanks for the reply. Is it possible to have 2 different columns installed (one capillary and one packed column) and have 2 different applications on the same instrument. Or is having one column idle when the other one is running, harmful at those elevated temperatures?

The main issue with trying to run two applications (assuming two different columns) is that they will have to share the same oven profile which will make it impossible to optimise separations on both. A compromise wil have to be found somewhere. But this is GC, compromise is the name of the game.

Rich

Yes I understand it would be difficult and this probably wouldn't work out. But I was only aiming for having to columns installed and running the analyses seperately, not at the same time. In other words not having to remove and install columns back and forth for two seperate applications is the goal for now. Now if compromise could be reached in order to have two applications running simultaneously, that would be fine too but it will require lots of method development first.

[Don_Hilton]

The limiting factor in having two columns mounted in the same GC oven is that the temperature of the GC oven is limited by the uppler limit of the column that will stand the lower temperature. A typical wax type column capillary can only take about 260 degrees for maximum temperature. A methyl silicone column can go up to around 350. If you have one of each of these columns in a GC oven, there is a significant limit to whay you can do on the methyl silicone column because of the limitations on the wax column.

[lgchrom]

The one column would be HP-1 and the other one HP-5. Both of which

For one application with the HP-5 I have the following conditions:

Column Temp. 320oC
Oven programming temperatures: Initial 235oC for 6 min. and then
rising at 2oC/min. up to 285oC.

For the other one with the HP-1

Oven: 170 °C (0,1 min); 170 °C to 350 °C (6 °C/min); 350 °C isotherm (20 min)


I am not sure if I could fit those two applications in a single run with such different conditions but then again they are not applications that require perfect seperations.

One app is total wax determination (total areas of many peaks compared to IS)

The other one compares one org. compound to an internal standard.

No calibration curves are needed so maybe I could get them to run on

Or maybe I could switch the column for one of the two apps.

I'll have to do some more research.

Thanks for the replies!

[Peter Apps]

These two phases are so similar that it would certainly be worthwhile to check whether you can do both separations on one or the other of them.

Peter