GC Separation

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jn2008's picture
GC Separation

I am trying to separate Pyridine, Methyl Iso Butyl Ketone and Toluene in a mixture using G43 column on an Agilent 7890 instrument. The method was developed successfully on PE 600 with a reslution of 2 between each peak. But on Agilent Pyridine and MIBK elutes together. I tried using a longer column, with various oven ramping conditions with no better results.
Any suggestions anyone?

Dr. Analytical
Dr. Analytical's picture
Please give us some

Please give us some information on the separation conditions: carrier, flow/pressure, temperature program, injection info (inlet type and conditions), and column dimensions.  I am assuming FID.
Was this the same column used on both systems?

jn2008's picture
Carrier - Helium@ 5ml/min,

Carrier - Helium@ 5ml/min, Split 1:5
Injector Temp: 140degrees, FID at 250 degrees
Oven: 35-hold 20 min, increase @10degrees to 220degrees hold 5 min
(I am analyzing 13 other solvents too in this method which is why I am holding for 20 min.Pyridine, MIBK and Toluene elutes after 23 min.)
HS injection, Thermostat for 30 min at 105 degrees
 Column - G43 30m 0.53mmID 3umdf
The same column was used in the systems + I tried 60m of the same column to get them separated which did not make any difference, surprisingly!

Dr. Analytical
Dr. Analytical's picture
This sounds like the USP 467

This sounds like the USP 467 method.
Is this the same column, or just the same type?  And how did you translate the HeadSpace conditions from the PE to Agilent systems?  Are you sure you have the peak identification correct?  Is peak shape OK?  What about peak width?
It is possible that you may have an injection problem related to the HS unit.

jn2008's picture
It is based on USP<467> and

It is based on USP<467> and the column is exactly the same.
I put the same exact parameters on HS that I used on PE.
Transferline temp:110
Needle Temp: 110
Thermostat @105 for 30 min.
Inj vol:0.08min by time
Loop fill(which is not there on PE): 0.05min
I don't have an MS, but I identified each peak RT by injecting the stock solutions. Peak shape and width are good for all other solvents. I doubt since Pyridine, MIBK and Toluene has close boiling points and molecular weights, it is not getting separated. I use Helium as makeup gas instead of Nitrogen. On PE there os no makeup gas parameter.

Dr. Analytical
Dr. Analytical's picture
Your problem is unusual.  I

Your problem is unusual.  I have some other questions and suggestions.
You said that you verified retention times by injection of the individual standards.  Was that injection using the autosampler or the headspace?  If the autosampler, repeat the experiment for pyridine and MIBK using the headspace. 
Are you using the Agilent headspace?  Which model?  How is the headspace connected to the GC?  Is the transfer line part of the carrier flow or does the transfer line go through the septum.  Are there any "cold spots" in the transfer line?  On some GC systems, the tubing between the transfer line and the injector can be long.  If it is not heated, you then have a cold spot which can trap some analytes.
Also, pyridine is sensitive to active sites in the system.  Is pyridine peak shape acceptable?

Dr Prashant Shihora
Dr Prashant Shihora's picture
u give some more idea abt

u give some more idea abt flowrate, temp & condition

jn2008's picture
I have given all the details

I have given all the details in the previous posts.