Saving carrier gas

[cene]

Hi all,

I am using a Shimadzu 2010 GC coupled to a QP2010 Ultra MS. I am trying to save as much carrier gas as possible during standby. Can anyone recommend what kind of flow settings to use to save as much gas as possible? Currently I have 15ml/min flowing through the system in total. 1ml/min through the column, with 3ml/min purge flow and the split closed. Can I lower these values any lower?

Any suggestions are appreciated.

[Peter Apps]

With flows any lower than you have you run the risk that a small leak will drop inlet pressure and the system will shut down.

You do not save any gas by closing the split - all it does is re-route the same flow inside the inlet pneumatics. Open the split to reduce inlet crud being transferred to the column.

Peter

[Consumer Products Guy]

Consider using hydrogen as carrier gas. Hydrogen generator preferred. Nitrogen as make-up gas.

[Steve Reimer]

Hydrogen does not work and play well with most mass specs. I have one system that only gets occasional use where it is set to use nitrogen at idle. I do have to return it to helium the day before use to purge.
Agilent sells a system to do this with their new systems, but they have a better way to switch over so it doesn't take very long to purge out the nitrogen.

[James_Ball]

I have plumbed in a two in/one out switching valve at the back of one of my instruments that I use for method development. I have Helium and Hydrogen so I switch between the two testing them as carriers in new methods. The valves are less than $200 from Swagelok or Parker which I can get through Restek or other supply vendors. It is quick and easy, you just have to remember to look at which way the valve is positioned before you begin. To make it easier you could mount it above the instrument so it is in easy view. You could use Helium/Nitrogen if you are only using it for standby.

[MSCHemist]

That would be my recommendation as well. Have a valve with two gasses He and H2/N2 and switch to He before running. Otherwise you can't go lower than 15ml/min in gas saver on most instruments.

I considered going hydrogen but I depend a lot on library hits and H2 reduces the match by shifting peaks +1 m/z. My MS has trouble enough already differentiating a lot of isomers (especially terpenes). Also I don't think I have heard one account yet of someone who switched and experienced no issues.

[Steve Reimer]

There have been problems with chlorinated solvents plus hydrogen in a hot inlet. I know of one lab that tried to switch and destroyed an inlet.

Reactivity can be a problem for some analytes.

As always, your mileage may vary

[James_Ball]

There have been problems with chlorinated solvents plus hydrogen in a hot inlet. I know of one lab that tried to switch and destroyed an inlet.

Reactivity can be a problem for some analytes.

As always, your mileage may vary

I ran one of our Agilent5973/EST systems with H2 for about 6 months testing. Never could get it to pass BFB, but after that when switching back to Helium, that system was the cleanest I have ever seen.

Running H2 as a standby gas could help clean out a system, if the inlets are inert enough.

[cene]

Thank you all for the replies. Looks like it will stay at 15ml/min for now. We use helium as our carrier gas and do not have the capacity to switch between multiple gases.

Peter - is closing off the split recommended just for Shimadzu GCs or all instruments?

[Peter Apps]

Peter - is closing off the split recommended just for Shimadzu GCs or all instruments?

I recommend keeping the split OPEN when on standby - this uses the same amount of gas as with the split closed but reduces the transfer of contaminants from the inlet to the column - most of the contaminants go out down the split.

As far as I know all current GCs simply re-route the gas flow when switching from split to splitless - the advice applies to all of them.

Peter

[cene]

Peter - is closing off the split recommended just for Shimadzu GCs or all instruments?

I recommend keeping the split OPEN when on standby - this uses the same amount of gas as with the split closed but reduces the transfer of contaminants from the inlet to the column - most of the contaminants go out down the split.

As far as I know all current GCs simply re-route the gas flow when switching from split to splitless - the advice applies to all of them.

Peter

Thanks Peter. I will keep the split open. Good to know I'm already running at the minimum flow rates.