Any one has experience with 1 GC with 2 columns??

[Cest]

I recently started to work on the Perkin Elmer Autosystem GC with FID & split/splitless injector.
The column installed is SP 2380, 100 m*0.25 mm*0.2 um, and is used to analyze long chain fatty acid (LCFA).
Another column also installed in this GC is a 30 m capillary column for volatile fatty acid (VFA).

I just wonder anyone has used 1 GC with 2 columns for different things, as long as the temperature range work for both columns? Does that work well? I'm asking because I recently spent one day using the 100 m column after over 1 week's analysis using 30 m column on this GC. And I found it took longer to stabilize the GC to test standard for LCFA. The next day, when I started to use 30 m column for VFA, the baseline has a lot of noises that never happened before.

Thank you.

[dblux_]

...I just wonder anyone has used 1 GC with 2 columns for different things, as long as the temperature range work for both columns?

That's what two channel GCs are made for

Does that work well? I'm asking because I recently spent one day using the 100 m column after over 1 week's analysis using 30 m column on this GC. And I found it took longer to stabilize the GC to test standard for LCFA. The next day, when I started to use 30 m column for VFA, the baseline has a lot of noises that never happened before.

Thank you.

Do you sustain carrier gas flow through both columns ?

[Cest]

...I just wonder anyone has used 1 GC with 2 columns for different things, as long as the temperature range work for both columns?

That's what two channel GCs are made for

Does that work well? I'm asking because I recently spent one day using the 100 m column after over 1 week's analysis using 30 m column on this GC. And I found it took longer to stabilize the GC to test standard for LCFA. The next day, when I started to use 30 m column for VFA, the baseline has a lot of noises that never happened before.

Thank you.

Do you sustain carrier gas flow through both columns ?

dblux_:
I leave helium (the carrier gas) at least 5-10 psi (Perkin Elmer GC has a screen showing psi of carrier gas going through columns) flowing through both columns and the oven temp at 50C when they are not in use. Sometimes, the other lab mate leaves the oven 150C overnight with 5-10 psi of helium. I'm new in this lab and it has not been in a standard protocol what appropriate temperature it should be for oven when they are not in use. But I think if it's high temp in oven, the helium flow should be set as high as it is when GC is running normally, in our case, about 40 psi. Please comment on that if you would.
Thanks.

[dblux_]

I leave helium (the carrier gas) at least 5-10 psi (Perkin Elmer GC has a screen showing psi of carrier gas going through columns) flowing through both columns and the oven temp at 50C when they are not in use. Sometimes, the other lab mate leaves the oven 150C overnight with 5-10 psi of helium. I'm new in this lab and it has not been in a standard protocol what appropriate temperature it should be for oven when they are not in use. But I think if it's high temp in oven, the helium flow should be set as high as it is when GC is running normally, in our case, about 40 psi. Please comment on that if you would.
Thanks.

For 100 m/0.25 µm column at 150C and 5 psi carrier flow is 0.06 mL/min ie. an unretain substance will flow through this column in 63 minutes.
I always try to leave carrier gas flow 0.5 mL/min. through columns not in use.
Try higher flows and check if it helps to have your columns better conditioned.

[Cest]

I leave helium (the carrier gas) at least 5-10 psi (Perkin Elmer GC has a screen showing psi of carrier gas going through columns) flowing through both columns and the oven temp at 50C when they are not in use. Sometimes, the other lab mate leaves the oven 150C overnight with 5-10 psi of helium. I'm new in this lab and it has not been in a standard protocol what appropriate temperature it should be for oven when they are not in use. But I think if it's high temp in oven, the helium flow should be set as high as it is when GC is running normally, in our case, about 40 psi. Please comment on that if you would.
Thanks.

For 100 m/0.25 µm column at 150C and 5 psi carrier flow is 0.06 mL/min ie. an unretain substance will flow through this column in 63 minutes.
I always try to leave carrier gas flow 0.5 mL/min. through columns not in use.
Try higher flows and check if it helps to have your columns better conditioned.

Will do and will update here.
Thanks!

[AICMM]

Cest,

Just a quick clarification if I may. Two columns, two inlets, and two detectors, right?

Also, a cyano column is probably not the best to bake overnight, especially with low flow as pointed out.

Best regards,

AICMM

[Cest]

Cest,

Just a quick clarification if I may. Two columns, two inlets, and two detectors, right?

Also, a cyano column is probably not the best to bake overnight, especially with low flow as pointed out.

Best regards,

AICMM

AICMM,
Yes, two columns, two inlets and two detectors.
Thanks for the info! It is good to know. Speaking of "bake", how high the temp is when you call it "bake"?
BTW, the other 30m column is Restek stabilwax®-DA Column (polar phase; Crossbond® acid-deactivated Carbowax® polyethylene glycol—for acidic compounds). Do you know if this column is ok if we "bake" it overnight?
Thanks.
Cest

[dblux_]

There is no need to leave GC oven in high temperature if no chromatographic runs are executed.
If you really want your GC to be ready next day leave inlet and detector in elevated temeratures, but decrease oven temperature.
BTW - Carbowax is not as resistant as DB-1 or DB-5, especially for traces of oxygen in carrier gas.

[Cest]

There is no need to leave GC oven in high temperature if no chromatographic runs are executed.
If you really want your GC to be ready next day leave inlet and detector in elevated temeratures, but decrease oven temperature.
BTW - Carbowax is not as resistant as DB-1 or DB-5, especially for traces of oxygen in carrier gas.

I usually leave oven a 30C and low flow of helium when not in use if it is not too long. No need to waste helium with high temp. We have a high volume of samples each day and my lab mate has been leaving oven at 150C since the start of work day, when someone told them to..
I will try your method and see how it goes.
Thanks.

[Cest]

Here is the update.
What we did is:
After all the sample runs were done yesterday, we left the oven at 50C, injector and detector at 250C and helium at 15 psi overnight.
Please see the attached.
The top chromatograph is the last sample yesterday, the bottom one is the first sample this morning.
The baseline did get worse, although it's not big difference, but noticeable.

Anyone has ideas what could be the cause?

[Peter Apps]

That baseline ripple is suspiciously regular, you might have a problem with detector gas flows, or something in the electronics.

Peter

[dblux_]

...The top chromatograph is the last sample yesterday, the bottom one is the first sample this morning.
The baseline did get worse, although it's not big difference, but noticeable.
...

Hi,
for me both chromatograms are almost the same.

You should run at least one blank before a sample when you start new day.
Then, when your baseline is OK you may start analysing samples.
Compare the 2nd sample with last sample from the previous day. First run is always a form of conditioning GC and column

[dblux_]

That baseline ripple is suspiciously regular, you might have a problem with detector gas flows, or something in the electronics.
Peter

Cest, what is your source of hydrogen ? Is it gas generator or cylinder ?
What about compressed air ? From gas cylinder or from compressor ?

[Cest]

That baseline ripple is suspiciously regular, you might have a problem with detector gas flows, or something in the electronics.
Peter

Cest, what is your source of hydrogen ? Is it gas generator or cylinder ?
What about compressed air ? From gas cylinder or from compressor ?

They are all from cylinders.
And actually by the end of day, after continually running samples, the baseline did not get any better..

[dblux_]

That baseline ripple is suspiciously regular, you might have a problem with detector gas flows, or something in the electronics.
Peter

Cest, what is your source of hydrogen ? Is it gas generator or cylinder ?
What about compressed air ? From gas cylinder or from compressor ?

They are all from cylinders.
And actually by the end of day, after continually running samples, the baseline did not get any better..

Then probably it's not detector gas flows related.
The simplest method of diagnosing would be to change the column. If new column has similar pattern then you would have to investigate further.
If new column has flat baseline then the old one is deteriorated.

BTW - this baseline is acceptable for me