Chromatography Forum

Has anyone know if it is possible to have three detectors on a GC? We are trying to incorporate a MS, TCD, and FPD onto a GC and didn't know if that was at all fessible. I know that every GC i've seen has 2 injection ports max but didn't know if there was a way to incorporate some kind of split column for the TCD and FPD.
Thanks
JEH

Depends on your GC, and on what you are trying to achieve.

What kind of samples are you trying to run? Could you do simultaneous injections on two columns? Do you always need all three detectors at once, or are you trying to do multiple methods that require different detectors on one instrument?

Basically we are trying to run jet fuel and find everything from NOx, SOx, and organics. I believe that a PFPD might be better than a FPD and then to maybe split the line on one of the columns.

Press-fit Y connectors allow you to split the column effluent to as many detectors as you want.

Obviously the sensitivity of detection goes down in proportion to the number of splits, and if you split too much the gas flows in the split lines can become too slow, so you may need to use silica tube with a narrower bore than the column to avoid peak broadening.

If you have a split to an MS the vacuum will suck all the sample to the MS unless you use very narrow bore silica (50 or 100 micron) trimmed to length to provide the right flow rate.

Another potential problem to be aware of is that the ratio of the post-column splits might change slightly as you programme the oven temperature, due to gas viscosity changes.

Peter

I do not think your problem is a GC with the right detector combination but a sample preparation/injection protocol to get your sample into the GC and then a set of columns to separate. Check exactly what you need to do. If you need to exactly define the make up of a Jet fuel I think you need a lab full of kit not just a GC with three detectors. Define your requirements, compounds levels, etc. Perhaps it will be simpler than I think

Hi Jhobbs
You can use one injection port for MSD, another one is for 2 detectors by using splitter.
Another suggestion is; you can use a "dean switch" which is a new technique found by agilent technologies. You can use 3 detectors at the same time by one injection -also 1 injection port-

Thanks
Savas
SEM Lab. Co
Ankara/Turkey

If I understand correctly, you want to use all three detectors at the same time, on one run of each sample.

In that case a Deans switch is not going to help, because it switches between detectors (columns, traps or whatever) rather than splitting the flow to multiple detectors.

The Deans switch goes back to before glass capillary columns, Deans published the design in 1968.

Peter

JHobbs,
Have you looked at recent Agilent application note "Screening for Hazardous Chemicals in Homeland Security and Environmental Samples Using a GC/MS/ECD/FPD with a 731 Compound DRS Database"?
It describes splitting the column effluent to 2 or 3 detectors depending on the configuration.
WK

Spliting off the column will decrease your sensitivity and since the TCD is non-destructive, you can run some guard column from the exhaust line of the TCD into the FPD. So you'll have, injector->column->TCD->guard column->FPD. Remember that the make-up gas for the TCD will be added into the FPD.