Column Change

[ucanmoruk]

Hi!

I am using a Agilent 7890B GC and 5977B MS system.

I have different analysis. VOC and Phthalate. They are so different from each other. One of them split, the other splitless. So they have different liner models. Also colums are different.

My question is that: If i change the column each week, is there a problem on the gc? or When i changed the column how much i wait for the gc is stable for the analysis?

[tkubowicz]

Hello

GC is designed to use different columns, different liners, different methods. So there is no harm for GC when you change those things. All you need is to do it properly.
Time for GC to stabilize with new (used) column depends on column condition, length, film thicknes etc. So there is no simple answer - I'd say: bakeout your column until you have stable baseline and no peaks coming out from column.

Regards

Tomasz Kubowicz

[Rndirk]

It's possible, but i try to avoid it in GC.

If you go for regular column switching with GC-MS it would be a good idea to use a piece of uncoated column connecting the analytical one with the MS. In this way you don't have to vent the MS to switch columns.

On a sidenote, the newest GC's (Agilent from what i've heard but i guess other manufacturers are also moving towards this) have plug-and-click systems to switch columns much easier. Anyone have hands-on experience with this?

[tkubowicz]

Hello

It's possible, but i try to avoid it in GC.

If you go for regular column switching with GC-MS it would be a good idea to use a piece of uncoated column connecting the analytical one with the MS. In this way you don't have to vent the MS to switch columns.

On a sidenote, the newest GC's (Agilent from what i've heard but i guess other manufacturers are also moving towards this) have plug-and-click systems to switch columns much easier. Anyone have hands-on experience with this?

You're probably meant Quick Swap. Just keep in mind that
due to the dilution effect of the purge gas, use of the QuickSwap device will result in some loss in sensitivity for MSD

Regards

Tomasz Kubowicz

[Rndirk]

Hello

It's possible, but i try to avoid it in GC.

If you go for regular column switching with GC-MS it would be a good idea to use a piece of uncoated column connecting the analytical one with the MS. In this way you don't have to vent the MS to switch columns.

On a sidenote, the newest GC's (Agilent from what i've heard but i guess other manufacturers are also moving towards this) have plug-and-click systems to switch columns much easier. Anyone have hands-on experience with this?

You're probably meant Quick Swap. Just keep in mind that
due to the dilution effect of the purge gas, use of the QuickSwap device will result in some loss in sensitivity for MSD

Regards

Tomasz Kubowicz

No, I was under the impression that changing analytical columns, if you're fast, can be done without venting/pumping the MS if there is a piece of column that stays connected to the MS. Maybe reducing the temperature of the MS source/quads during this operation to be safer. Without using a second gas flow. So yes, the quick swap thing but without a second EPC, just a simple column connection.

In my second paragraph i was referring to this.

[rb6banjo]

I've never used this but I think you're looking for something like this:

http://www.restek.com/pdfs/203-03-023.pdf

I don't have to do a lot of column switching in my systems. Most of my work involves headspace analysis and I'm blessed to have a number of systems in my lab - each has a different column or combination of columns (the best is my Agilent system with their Dean's switch installed so I can get the best of all worlds buy using heartcutting techniques) so that I can merely go from one system to another until I find a separation I like.

[ucanmoruk]

Ok. Then when i change the gc column, what can i do to come gc a stabile state. How much i wait for it?

[tkubowicz]

Hello

Ok. Then when i change the gc column, what can i do to come gc a stabile state. How much i wait for it?

See my previous post

Regards

Tomasz Kubowicz

[rb6banjo]

Probably the single most important thing is to make sure you don't have an air leak. I'd let it sit for 20-30 minutes and then tune the mass spec. to make sure your water and air are good. If that checks out, then you're you have a good seal. After that, Tomasz's comments apply. Make sure you have an acceptable baseline before you start analyzing real samples.

[James_Ball]

If you vent MS then you will be looking at 1-2 hours to equilibrate the temperatures again.

I solved the problem with switching columns by installing two columns, using two injection ports and a metal Y connector at the MS interface. Be sure your analytical columns are 0.25 ID or smaller and the transfer line into the MS is 0.53, otherwise the GC will not calculate the correct head pressure to give correct column flows. The 0.53ID transfer lines allows for a vacuum to form at the outlet of the analytical columns in the Y connector. When using the front column set the flow to 1-1.2ml/min and the rear column flow to 0.3-0.4ml/min and vice versa when using the rear column. I have had mine working for two years like this with no problems. If you need to change a column, just raise the opposite column flow up to 3-4ml/minute and it will keep most of the air from entering the MS and allows for the instrument to be ready again quickly.

http://www.restek.com/catalog/view/3355

That is the connector I use in this setup. You can also use the 0.53 MXT metal transfer line so you don't have to worry as much about breaking the transfer line.

[tdgcuser]

From the standpoint of "do no unnecessary maintenance" I have to ask why you need to change the column for VOC's and phthalates. Just crank the oven temperature up a little higher and look for the 149. It WILL be there.

Old school column changes without venting? Bad idea. Those of us that have done it eventually regret it. Take your time and do it right.

You will have to determine for yourself which liner works best for your combination of analytes, solvents, splits and inlet conditions.

[ucanmoruk]

http://www.restek.com/catalog/view/3355

That is the connector I use in this setup. You can also use the 0.53 MXT metal transfer line so you don't have to worry as much about breaking the transfer line.

Thanks for your advice. I am investigating the connector. One of my column is HP-5MS is length 30 m - Diam. 0.250 mm - Film 0.25 µm and one of is
DB - VRX Length - 60m / Diam - 0.250 mm / Film - 1.40 um.

You will have to determine for yourself which liner works best for your combination of analytes, solvents, splits and inlet conditions.

The column that i am using for phthalate is HP-5MS is length 30 m - Diam. 0.250 mm - Film 0.25 µm.
My method on this column about 8 min. and that's important for me. I can't extend the duration.

When i try the VOC analysis with this column, the peaks are overloaded and the result is unsuccessful. I wrote here:

viewtopic.php?f=2&t=37761

I need a thicker column for VOC analysis and that's the other column on my hand.
DB - VRX Length - 60m / Diam - 0.250 mm / Film - 1.40 um.